CN114730570B - Spin torque oscillator with antiferromagnetically coupled auxiliary layer and method of operation thereof - Google Patents
Spin torque oscillator with antiferromagnetically coupled auxiliary layer and method of operation thereof Download PDFInfo
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- CN114730570B CN114730570B CN202080079839.2A CN202080079839A CN114730570B CN 114730570 B CN114730570 B CN 114730570B CN 202080079839 A CN202080079839 A CN 202080079839A CN 114730570 B CN114730570 B CN 114730570B
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- G—PHYSICS
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- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
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Abstract
A spin torque oscillator includes a first electrode, a second electrode, and a device layer stack between the first electrode and the second electrode. The device layer stack includes: a spin-polarized layer comprising a first ferromagnetic material; an auxiliary layer comprising a third ferromagnetic material; a ferromagnetic oscillating layer comprising a second ferromagnetic material positioned between the spin-polarizing layer and the auxiliary layer; a nonmagnetic spacer layer located between the spin-polarizing layer and the ferromagnetic oscillating layer; and a nonmagnetic coupling layer between the ferromagnetic oscillating layer and the auxiliary layer. The auxiliary layer is antiferromagnetically coupled to the ferromagnetic oscillating layer by a nonmagnetic coupling layer, and the auxiliary layer has a magnetization coupled to the magnetization of the ferromagnetic oscillating layer.
Description
RELATED APPLICATIONS
The present application claims the priority benefits of the following patent applications: U.S. non-provisional patent application Ser. No. 16/887,563, filed 5/29/2020; and U.S. non-provisional patent application No. 16/887,715, filed 5/29/2020, the entire contents of which are hereby incorporated by reference for all purposes.
Technical Field
The present disclosure relates generally to the field of microelectronic magnetic devices, and in particular to spin torque oscillators with antiferromagnetically coupled assist layers and methods of operation thereof.
Background
Periodic pulse patterns with frequencies in the gigahertz range are employed in many electronic applications, such as wireless communication systems, radar, wireless network devices, automotive communication devices, and acoustic synthesizers. While many Spin Torque Oscillator (STO) devices are known in the art that generate periodic pulses at frequencies greater than 10GHz, many such STO devices have a wide peak width and a low Q factor at the oscillation frequency.
Disclosure of Invention
According to an embodiment of the present disclosure, a spin torque oscillator includes a first electrode, a second electrode, and a device layer stack between the first electrode and the second electrode. The device layer stack includes: a spin-polarizing layer comprising a first ferromagnetic material, an auxiliary layer comprising a third ferromagnetic material, a ferromagnetic oscillating layer comprising a second ferromagnetic material between the spin-polarizing layer and the auxiliary layer, a nonmagnetic spacer layer between the spin-polarizing layer and the ferromagnetic oscillating layer, and a nonmagnetic coupling layer between the ferromagnetic oscillating layer and the auxiliary layer. The auxiliary layer is antiferromagnetically coupled to the ferromagnetic oscillating layer by a nonmagnetic coupling layer, and the auxiliary layer has a magnetization coupled to the magnetization of the ferromagnetic oscillating layer.
In a first embodiment, an electromagnet is located near the device layer stack and is configured to direct a bias magnetic field through the device layer stack. In a second embodiment, at least one of the first or second electrodes comprises a ferromagnetic material having a fixed magnetization and comprises a ferromagnetic electrode layer and a ferromagnetic post protruding from the ferromagnetic electrode layer towards the device layer stack, the ferromagnetic post having a lateral width substantially the same as a lateral width of the device layer stack and the lateral width of the ferromagnetic electrode layer being greater than the lateral width of the ferromagnetic post such that an annular horizontal surface of the ferromagnetic electrode layer surrounds a base of the ferromagnetic post to provide a recess at a junction of the ferromagnetic electrode layer and the ferromagnetic post.
Drawings
Fig. 1A and 1B are vertical cross-sectional views of two alternative configurations of a first exemplary spin torque oscillator according to a first embodiment of the present disclosure.
Fig. 2 is a schematic diagram of a first exemplary periodic signal generator according to a first embodiment of the present disclosure.
Fig. 3 is a schematic diagram of a second exemplary periodic signal generator according to a first embodiment of the present disclosure.
Fig. 4A is a vertical cross-section of a first exemplary spin torque oscillator in the absence of an external magnetic field and in the absence of spin current according to a first embodiment of the present disclosure.
Fig. 4B is a vertical cross-sectional view of a first exemplary spin torque oscillator in the presence of an external magnetic field and in the absence of spin current according to a first embodiment of the present disclosure.
Fig. 4C is a vertical cross-sectional view of a first exemplary spin torque oscillator in the presence of an external magnetic field and in the presence of a spin current according to a first embodiment of the present disclosure.
Fig. 5 is a vertical cross-section of a second exemplary spin torque oscillator according to a second embodiment of the present disclosure.
Fig. 6 is a schematic diagram of a third exemplary periodic signal generator according to a second embodiment of the present disclosure.
Fig. 7 is a schematic diagram of a fourth exemplary periodic signal generator according to a second embodiment of the present disclosure.
Fig. 8 is a vertical cross-sectional view of a second exemplary spin torque oscillator in the presence of spin current according to a second embodiment of the present disclosure.
Fig. 9 is a vertical cross-section of a parallel connection of two second exemplary spin torque oscillators according to a second embodiment of the present disclosure.
Detailed Description
As noted above, the present disclosure is directed to STO with antiferromagnetically coupling assist layers and methods of operation thereof, various aspects of which are described in detail below. STO with antiferromagnetically-coupled auxiliary layer has a narrower peak width at the oscillation frequency, which provides improved Q-factor and performance in various communication devices or other devices employing STO.
The figures are not drawn to scale. Multiple instances of an element may be repeated where a single instance of the element is illustrated therein unless repetition of the element is explicitly described or otherwise clearly indicated as not being present. Numbers such as "first," "second," and "third" are used merely to identify similar elements, and different numbers may be employed throughout the specification and claims of this disclosure. The term "at least one" element is intended to encompass both the possibility of a single element and the possibility of multiple elements.
The same reference numerals indicate the same or similar elements. Elements having the same reference number are assumed to have the same composition and the same function unless otherwise specified. Unless otherwise indicated, "contact" between elements refers to direct contact between elements that provides a shared edge or surface of the elements. Two or more elements will be "separated" from one another if they are not in direct contact with one another. As used herein, a first element positioned "on" a second element may be positioned on the outside of the surface of the second element or on the inside of the second element. As used herein, a first element is positioned "directly on" a second element if there is physical contact between the surface of the first element and the surface of the second element. As used herein, a first element is "electrically connected to" a second element if there is a conductive path between the first element and the second element that is comprised of at least one conductive material. As used herein, "magnetization" refers to the direction of magnetization of a magnetic material.
As used herein, "layer" refers to a portion of material that includes regions having a thickness. The layer may extend over the entirety of the underlying or overlying structure, or may have a range that is less than the range of the underlying or overlying structure. The layers may extend horizontally, vertically and/or along a tapered surface. The substrate may be a layer, may include one or more layers therein, or may have one or more layers thereon, and/or thereunder.
As used herein, a first surface and a second surface "vertically coincide" with each other if the second surface is above or below the first surface and if there is a vertical plane or a substantially vertical plane comprising the first surface and the second surface. A substantially vertical plane is a plane that extends straight in a direction that deviates from the vertical by an angle of less than 5 degrees. The vertical plane or substantially vertical plane is straight along a vertical direction or substantially vertical direction and may or may not include curvature along a direction perpendicular to the vertical direction or substantially vertical direction.
Fig. 1A and 1B illustrate two different configurations of a first exemplary spin torque oscillator 100 according to a first embodiment of the present disclosure. STO 100 includes a first electrode 110. In the configuration of fig. 1A, where the poles 250 of an electromagnet, which will be described below, are not electrically connected to the first electrode 110, the first electrode 110 may comprise any suitable electrically conductive material. In one embodiment, the first electrode comprises a non-magnetic conductive material, such as a metal (e.g., al, W, ti, cu, etc.), a metal alloy, or a metal nitride (e.g., tiN, WN, taN, etc.).
In the configuration of fig. 1B, wherein the material of the pole 250 is also used to form the first electrode 110, and the pole 250 contacts the first electrode 110, the first electrode may comprise any suitable first soft magnetic material. As used herein, soft magnetic material refers to ferromagnetic materials having an intrinsic coercivity of less than 1000A/m. Soft magnetic materials are easily magnetized and demagnetized and can be used to enhance and/or direct the magnetic flux generated by an electrical current. Exemplary soft magnetic materials that may be used for the first electrode 110 include nickel-iron alloys, soft ferrites, and nickel-iron-chromium alloys. In one embodiment, the first soft magnetic material of the first electrode 110 may have an intrinsic coercivity in the range of 1A/m to 100A/m.
The first electrode 110 may be formed on a substrate (not shown) having a thickness sufficient to provide mechanical support for the first electrode 110. For example, the substrate may be an insulating substrate (such as a quartz substrate or a ceramic substrate, such as a sapphire substrate), or a semiconductor substrate or a conductive substrate having an insulating layer (such as a silicon oxide or aluminum oxide layer) thereon, on which the first electrode 110 may be formed.
The STO device layer stack 111 is located on the top surface of the first electrode 110. The STO device layer stack 111 includes, from bottom to top or top to bottom, an optional nonmagnetic seed layer 112, a spin-polarizing layer 120 comprising a first ferromagnetic material, a nonmagnetic spacer layer 130, a ferromagnetic oscillating layer 140 comprising a second ferromagnetic material that may be the same or different than the first ferromagnetic material, a coupling layer 150, and an antiferromagnetic coupling assistance layer 160 comprising a third ferromagnetic material that may be the same or different than the first ferromagnetic material and the second ferromagnetic material, and has a magnetization that couples with the magnetization of the ferromagnetic oscillating layer 140. While the present disclosure is described with embodiments in which the layers of the device layer stack are arranged from bottom to top, embodiments in which the device layer stack is arranged from top to bottom are expressly contemplated herein.
The various layers of the device layer stack 111 may have vertically coincident sidewalls, i.e., sidewalls that lie in the same vertical plane. The horizontal cross-sectional shape of each layer within the device layer stack 111 may be the same or may be substantially the same where their sidewalls have a non-zero taper angle. The horizontal cross-sectional shape of the device layer stack 111 may be circular, elliptical, rectangular, rounded polygons (i.e., polygons modified to provide rounded corners), or any generally non-intersecting closed two-dimensional curvilinear shape. The lateral dimensions (such as the diameter or sides of the rectangle) of the device layer stack 111 may be in the range of 10nm to 200nm, such as 20nm to 100nm, although smaller and larger lateral dimensions may also be employed.
An optional non-magnetic seed layer 112 may be used to enhance the crystalline properties of the material layer deposited thereon. For example, the nonmagnetic seed layer 112 may include chromium, copper, tantalum, ruthenium, hafnium, niobium, tungsten, nickel-aluminum alloy, or combinations or alloys thereof. The thickness of the nonmagnetic seed layer 112 may be in the range of 1nm to 2nm, but smaller and larger thicknesses may also be employed.
The first ferromagnetic material of the spin-polarized layer 120 may include: fe, co, ni, ferromagnetic alloys comprising at least one of Fe, co and Ni, or magnetic heusler alloys, and/or may consist essentially of them. The spin-polarized layer 120 may have a thickness in the range of 1nm to 3nm, such as 1.2nm to 2nm, although lesser and greater thicknesses may also be employed. As will be discussed below, the thickness of the spin-polarized layer 120 may be determined based on the magnetic moment-thickness product of the spin-polarized layer 120, i.e., based on the product of the magnetic moment (which is the magnitude of magnetization) and the thickness of the spin-polarized layer 120.
The nonmagnetic spacer layer 130 comprises and/or consists essentially of a nonmagnetic metal, semiconductor material, or dielectric metal oxide material having a thickness that allows charge tunneling. For example, the nonmagnetic spacer layer 130 may include any of chromium, copper, tantalum, ruthenium, hafnium, niobium, tungsten, nickel aluminum alloy, zinc selenide, copper indium selenide, magnesium oxide, or aluminum oxide. The thickness of the nonmagnetic spacer layer 130 may be in the range of 0.8nm to 3 nm. In the case where a tunneling dielectric material is used for the nonmagnetic spacer layer 130, the thickness of the nonmagnetic spacer layer 130 may be in the range of 0.8nm to 1.2nm. The thickness of the nonmagnetic spacer layer 130 may be selected so that the combination of the spin-polarizing layer 120, the nonmagnetic spacer layer 130, and the ferromagnetic oscillating layer 140 functions as a spin valve or a magnetic tunnel junction.
The second ferromagnetic material of the ferromagnetic oscillating layer 140 may include: fe, co, ni, ferromagnetic alloys comprising at least one of Fe, co and Ni, or magnetic heusler alloys, and/or may consist essentially of them. The thickness of the ferromagnetic oscillating layer 140 may be in the range of 2nm to 15nm, such as 4nm to 10nm, but smaller and larger thicknesses may also be employed. The thickness of the spin ferromagnetic oscillation layer 140 may be determined based on the magnetic moment-thickness product of the ferromagnetic oscillation layer 140. In one embodiment, the ferromagnetic oscillating layer 140 has a larger magnetic moment-thickness product than the spin polarizing layer 120. In one embodiment, the ratio of the magnetic moment-thickness product of the ferromagnetic oscillating layer 140 to the magnetic moment-thickness product of the spin-polarized layer 120 may be in the range of 1.2 to 5, such as 2 to 4. Setting the ratio of the magnetic moment-thickness product of the ferromagnetic oscillating layer 140 to the magnetic moment-thickness product of the spin-polarized layer 120 in the range of 1.2 to 5 results in an antiferromagnetic alignment of the vertical component (i.e., the axial component) of the magnetization of the spin-polarized layer 120 with the vertical component of the magnetization of the ferromagnetic oscillating layer 140 during operation as a spin valve or as a magnetic tunnel junction. If the materials of the ferromagnetic oscillation layer 140 and the spin polarization layer 120 are the same, the thickness of the ferromagnetic oscillation layer 140 is 1.2 to 5 times that of the spin polarization layer 120. If the materials of the ferromagnetic oscillation layer 140 and the spin-polarizing layer 120 are different and have different magnetic moments, the thicknesses of the layers may be adjusted to obtain a magnetic moment-thickness product ratio in the range of 1.2 to 5.
The nonmagnetic coupling layer 150 includes and/or consists essentially of a metallic material that provides antiferromagnetic coupling between the ferromagnetic oscillation layer 140 and the antiferromagnetic coupling auxiliary layer 160. For example, antiferromagnetically coupling layer 150 may include and/or consist essentially of ruthenium, rhodium, and/or iridium. The thickness of the nonmagnetic coupling layer 150 may be in the range of 0.4nm to 2nm, such as 0.6nm to 1.5nm, but smaller and larger thicknesses may also be employed.
The third ferromagnetic material of the antiferromagnetic coupling aid layer 160 may include: fe, co, ni, ferromagnetic alloys comprising at least one of Fe, co and Ni, or magnetic heusler alloys, and/or may consist essentially of them. In the absence of a current flowing through the stack 111, the magnetization of the antiferromagnetic coupling auxiliary layer 160 is completely antiparallel to the magnetization of the ferromagnetic oscillating layer 140. However, as will be described below, the magnetization of the antiferromagnetic coupling auxiliary layer 160 may be completely or partially antiparallel to the magnetization of the ferromagnetic oscillation layer 140 under various operating conditions of the first exemplary spin torque oscillator 100. The thickness of the antiferromagnetic coupling auxiliary layer 160 may be in the range of 2nm to 100nm, such as 2nm to 20nm, although smaller and larger thicknesses may also be employed. As will be discussed below, the thickness of the antiferromagnetic coupling auxiliary layer 160 may be determined based on the magnetic moment-thickness product of the ferromagnetic oscillating layer 140. In one embodiment, the antiferromagnetic coupling assisting layer 160 has a greater magnetic moment-thickness product than the ferromagnetic oscillating layer 140. In one embodiment, the ratio of the magnetic moment-thickness product of the antiferromagnetic coupling auxiliary layer 160 to the magnetic moment-thickness product of the ferromagnetic oscillating layer 140 may be in the range of 2 to 10. Setting the ratio of the magnetic moment-thickness product of the antiferromagnetic coupling auxiliary layer 160 to the magnetic moment-thickness product of the ferromagnetic oscillation layer 140 in the range of 2 to 10 results in antiferromagnetic alignment of the in-plane component (i.e., horizontal component) of the magnetization of the antiferromagnetic coupling auxiliary layer 160 with the in-plane component of the magnetization of the ferromagnetic oscillation layer 140 during operation of the spin torque oscillator 100. If the materials of the antiferromagnetic coupling auxiliary layer 160 and the ferromagnetic oscillation layer 140 are the same, the antiferromagnetic coupling auxiliary layer 160 has a thickness 2 to 10 times that of the ferromagnetic oscillation layer 140. If the materials of the antiferromagnetic coupling assisting layer 160 and the ferromagnetic oscillation layer 140 are different and have different magnetic moments, the thicknesses of the layers can be adjusted to obtain a magnetic moment-thickness product ratio in the range of 2 to 10.
In general, the device layer stack 111 may be formed on the first electrode 110. The layer stack comprises, from bottom to top or top to bottom: a spin polarized layer 120 comprising a first ferromagnetic material, a nonmagnetic spacer layer 130, a ferromagnetic oscillating layer 140 comprising a second ferromagnetic material, a coupling layer 150 contacting the ferromagnetic oscillating layer 140, and an antiferromagnetic coupling assistance layer 160 comprising a third ferromagnetic material and having a magnetization coupled to the magnetization of the ferromagnetic oscillating layer 140. An optional nonmagnetic seed layer 112 may be formed directly on the top surface of the first electrode 110 below the other layers of the device layer stack 111. The device layer stack 111 may be formed as a pillar structure with vertical sidewalls.
The second (upper) electrode 190 may be formed directly on the top surface of the device layer stack 111. In one embodiment, the second electrode 190 may be directly formed on the top surface of the antiferromagnetic coupling auxiliary layer 160. The second electrode 190 may be formed of the same material as the first electrode 110.
Dielectric layer 220 surrounds device layer stack 111. Dielectric layer 220 comprises a dielectric material such as silicon oxide, silicon nitride, a dielectric metal oxide (e.g., aluminum oxide), or silicon carbide nitride.
An electromagnet 240 comprising an electrically conductive coil 230 surrounding a soft magnetic pole 250 is located near at least one side of the device layer stack 111. The conductive coil 230 comprises a conductive material such as copper, silver, gold, aluminum, tungsten, or ruthenium. Although a conductive coil 230 having a single loop is schematically illustrated in fig. 1A and 1B, embodiments of a coil 230 having multiple loops (such as a spiral around a pole) are expressly included herein.
The soft magnetic pole 250 comprises any soft magnetic material such as nickel-iron alloy, soft ferrite or nickel-iron-chromium alloy. In one embodiment, the soft magnetic material may have an intrinsic coercivity in the range of 1A/m to 100A/m. In the first configuration of STO 100 shown in FIG. 1A, dielectric layer 220 separates soft magnetic pole 250 from first and second electrodes (110, 190). In the second configuration of STO 100 shown in FIG. 1B, soft magnetic pole 250 is in contact with and made of the same soft magnetic material as the first and second electrodes (110, 190). In one embodiment, the electromagnet 240 and the device layer stack 111 may be embedded in the dielectric material layer 220.
The structure shown in fig. 1A and 1B is a first exemplary spin torque oscillator 100. The electromagnet 240 is configured to direct a bias magnetic field through the device layer stack 111 when the electromagnet is turned on by applying a current to the coil 230. A control circuit (not shown) is configured to apply a bias voltage or current between the first electrode 110 and the second electrode 190 to cause a spin current to flow through the device layer stack 111 between the electrodes (110, 190), as will be described in more detail below. The first exemplary spin torque oscillator 100 may be used to provide a periodic signal generator that may generate a periodic sinusoidal output or a periodic pulse pattern.
Referring to fig. 2, a first exemplary periodic signal generator according to a first embodiment of the present disclosure is shown. The first periodic signal generator includes the first exemplary spin torque oscillator 100, control circuit 305, and heterodyne mixer circuit shown in fig. 1A and 1B, which is configured to output periodic signals having frequencies in the range of 2GHz to 100GHz, and is described in s.kisilev et al, 9/25/2003, nature journal 425/380, the contents of which are incorporated herein by reference in their entirety. The first exemplary periodic signal generator may include a control circuit 305 configured to induce a direct current through the device layer stack 111 by applying a direct bias voltage between the first electrode 110 and the second electrode 190 to induce a spin current through the device layer stack 111 and/or to provide a current through the coil 230 of the electromagnet 240 to generate a magnetic field in the electromagnet 240.
Heterodyne mixer circuit includes an inductor 310 connected between a DC voltage source and the electrical output of STO 100. The output signal from the device layer stack 111 may be transmitted through the capacitor 320 to the operational amplifier 330. The output signal from the operational amplifier 330 may be mixed in a mixer 350 with the output signal from the scan signal generator 340. The output signal from the mixer 350 is fed to a bandpass filter 360. Filter 360 passes signals in the range of 25MHz to 100 MHz. The output signal from the bandpass filter 360 may then be amplified by another operational amplifier 370 and may pass through a diode detector 380 to generate a microwave frequency output signal. The first periodic signal generator may generate periodic pulse signals having a narrow pulse width in the range of 2GHz to 100GHz, such as 5GHz to 30GHz, although lower and higher frequencies may also be employed. Other output/mixer circuits may also be used.
Referring to fig. 3, a second exemplary periodic signal generator according to a first embodiment of the present disclosure is shown that may be derived from the first exemplary periodic signal generator of fig. 2 by connecting multiple instances (such as two or more instances) of the first exemplary spin torque oscillator 100 of fig. 1A and 1B in a parallel configuration. In this case, the first exemplary structure of fig. 1A and 1B may be modified to form a plurality of device layer stacks 111. Multiple instances of the spin torque oscillator 100 in the second exemplary periodic signal generator may generate stable high frequency output signals.
The device layer stack 111 may be tuned by a magnetic field from the electromagnet 240 or by a spin current generated by applying a bias voltage between the first and second electrodes (110, 190). Referring to fig. 4A, alignment of magnetization of component layers within the device layer stack 111 in the first exemplary spin torque oscillator 100 is shown in the absence of an external magnetic field (i.e., when no current is flowing through the coil 230 of the electromagnet) and in the absence of a bias spin current flowing through the device layer stack 111, according to a first embodiment of the present disclosure. While the structure of fig. 1A is shown in fig. 4A-4C, it should be understood that the structure of fig. 1B may be used instead.
Under such conditions, the magnetizations of the spin-polarized layer 120 and the ferromagnetic oscillation layer 140 may be ferromagnetically coupled, and the magnetizations of the ferromagnetic oscillation layer 140 and the antiferromagnetic coupling aid layer 160 may be antiferromagnetically coupled. For example, the magnetization of the ferromagnetic oscillation layer 140 and the magnetization of the spin-polarizing layer 120 may be in-plane magnetizations parallel to the interface between the spin-polarizing layer 120 and the nonmagnetic spacer layer 130, while the electromagnet 140 is turned off and spin current does not flow through the device layer stack 111. For example, the magnetization of the ferromagnetic oscillation layer 140 and the magnetization of the antiferromagnetic coupling assistance layer 160 may be in-plane magnetizations antiparallel to each other and parallel to the interface between the ferromagnetic oscillation layer 140 and the coupling layer 150, while the electromagnet 140 is turned off and spin current does not flow through the device layer stack 111.
Referring to fig. 4B, alignment of magnetization of component layers within the device layer stack 111 in the first exemplary spin torque oscillator 100 in the presence of an external magnetic field and in the absence of a bias spin current is shown, according to a first embodiment of the present disclosure. In this case, the electromagnet 240 may be turned on without applying a bias voltage between the first and second electrodes (110, 190). In other words, no spin current flows between the first electrode 110 and the second electrode 190. The electromagnet 240 may be turned on by passing a direct current through the conductive coil 230, which generates a magnetic field in the soft magnetic material pole 250. The magnetic field generated by electromagnet 240 is directed through soft magnetic material poles 250 and a bias magnetic field is generated within adjacent device layer stack 111 to tune the frequency of STO 100. The bias magnetic field aligns the various magnetizations of the magnetic layer (120,140,160) in a direction of the bias magnetic field, which may be up or down. In the illustrated example, the magnetization of the spin-polarized layer 120, the magnetization of the ferromagnetic oscillating layer 140, and the magnetization of the antiferromagnetic coupling auxiliary layer 160 may be aligned upward in the vertical direction.
The bias magnetic field is vertical within the device layer stack 111 and the magnitude of the bias magnetic field can be selected to overcome the antiferromagnetic alignment of the axial component (i.e., vertical component) of the magnetization of the ferromagnetic oscillating layer 140 and the axial component of the magnetization of the antiferromagnetic coupling aid layer 160. In other words, the bias magnetic field overcomes the tendency of the magnetization of the ferromagnetic oscillation layer 140 and the magnetization of the antiferromagnetic coupling assist layer 160 to antiferromagnetically couple with each other. Accordingly, the axial component of the magnetization of the ferromagnetic oscillating layer 140 and the axial component of the magnetization of the antiferromagnetic coupling auxiliary layer 160 may be parallel to the bias magnetic field while the electromagnet 240 is turned on. In one embodiment, the magnetization of the ferromagnetic oscillating layer 140 and the magnetization of the spin-polarizing layer 120 may be axial magnetizations parallel to the bias magnetic field, while the electromagnet 240 is on and spin current does not flow through the device layer stack 111.
Referring to fig. 4C, alignment of magnetization of component layers within the device layer stack 111 in the first exemplary spin torque oscillator 100 is shown in the presence of an external magnetic field generated by the electromagnet 140 and in the presence of a dc bias spin current when a current flows through the coil 230, according to a first embodiment of the present disclosure. A dc bias voltage may be applied between the first electrode 110 and the second electrode 190 to generate a spin current in the device layer stack 111. The bias magnetic field and the direction of the spin current in the device layer stack 111 may be antiparallel.
The magnetization of the spin-polarized layer 120 oscillates (e.g., precesses) with a lower spin current than the magnetization of the ferromagnetic oscillation layer 140. The magnetization of the ferromagnetic oscillation layer 140 oscillates (e.g., precesses) with a higher spin current, which results in a tilt and precession of the magnetization. The magnetization of the spin-polarized layer 120 (which has a lower magnetic moment-thickness product) follows the magnetization of the ferromagnetic oscillating layer 140 in an antiparallel direction, and the azimuth angle of the in-plane component of the magnetization of the ferromagnetic oscillating layer 140 may be the same as the azimuth angle of the in-plane component of the magnetization of the spin-polarized layer 120.
The layer stack of the spin-polarizing layer 120, the nonmagnetic spacer layer 130, and the ferromagnetic oscillating layer 140 functions as a spin valve or a magnetic tunnel junction depending on whether the nonmagnetic spacer layer is conductive or insulating. Spin polarization of the current occurs through a spin valve or through a magnetic tunnel junction. The spin-polarized electrons preferentially pass through the nonmagnetic spacer layer 130 such that the axial component of the magnetization of the spin-polarized layer 120 is antiferromagnetically aligned with the axial component of the magnetization of the ferromagnetic oscillating layer 140.
When the ratio of the magnetic moment-thickness product of the ferromagnetic oscillation layer 140 to the magnetic moment-thickness product of the spin-polarized layer 120 is in the range of 1.2 to 5, such as 1.4 to 3, the axial component of the magnetization of the ferromagnetic oscillation layer 140 may be aligned parallel to the bias magnetic field and the axial component of the magnetization of the spin-polarized layer 120 may be aligned antiparallel to the bias magnetic field to minimize the total energy of the magnetic configuration of the spin valve or the magnetic tunnel junction. However, this configuration is energetically unfavorable for the magnetization of the spin-polarized layer 120, and tilts the magnetization of the spin-polarized layer 120 from the vertical direction, thereby generating an in-plane component of the magnetization of the spin-polarized layer 120. In the presence of a bias magnetic field, the in-plane components of the magnetization of the spin-polarized layer 120 precess about the vertical direction.
The in-plane component of the magnetization of the spin-polarized layer 120 tilts the magnetization of the ferromagnetic oscillating layer 140 away from the vertical. The substantially ferromagnetic coupling between the magnetization of the spin-polarized layer 120 and the magnetization of the ferromagnetic oscillating layer 140 causes the tilt of the magnetization of the ferromagnetic oscillating layer 140 to be locked in the direction of the in-plane component of the magnetization of the spin-polarized layer 120. In other words, the in-plane component of the magnetization of the ferromagnetic oscillating layer 140 may have the same azimuth angle about the vertical axis as the in-plane component of the magnetization of the spin-polarized layer 120. Thus, the magnetization of the spin-polarized layer 120 and the magnetization of the ferromagnetic oscillating layer 140 precess synchronously around the vertical direction at the same precession frequency.
The axial component of the magnetization of the antiferromagnetic coupling aid layer 160 remains parallel to the direction of the bias magnetic field within the device layer stack 111 while the electromagnet 240 is turned on and a spin current flows through the device layer stack 111. Due to the antiferromagnetic nature of the coupling between the antiferromagnetic coupling auxiliary layer 160 and the ferromagnetic oscillation layer 140, the in-plane component of the magnetization of the ferromagnetic oscillation layer 140 and the in-plane component of the magnetization of the antiferromagnetic coupling auxiliary layer 160 are antiferromagnetically coupled to each other, while the electromagnet 240 is turned on and a spin current flows through the device layer stack 111. Thus, the auxiliary layer 160 increases the tilt angle of the magnetization of the ferromagnetic oscillating layer 140, which reduces the peak width of the signal output by the STO 100.
The magnetization of the antiferromagnetic coupling auxiliary layer 160 is coupled to the magnetization of the ferromagnetic oscillation layer 140 and precesses about the vertical axis at the same precession frequency as the magnetization of the spin polarization layer 120. The azimuthal angle of the in-plane component of the magnetization of the ferromagnetic oscillation layer 140 may be the same as the azimuthal angle of the in-plane component of the magnetization of the spin-polarized layer 120, and may be offset 180 degrees with respect to the azimuthal angle of the in-plane component of the magnetization of the antiferromagnetic coupling auxiliary layer 160.
According to one aspect of the present disclosure, the ratio of the magnetic moment-product thickness of the antiferromagnetic coupling auxiliary layer 160 to the magnetic moment-product thickness of the ferromagnetic oscillation layer 140 is in the range of 2 to 10 to provide stability to the vertical component of the antiferromagnetic coupling auxiliary layer 160 to ensure that the vertical component of the antiferromagnetic coupling auxiliary layer 160 remains parallel to the bias magnetic field while providing sufficient antiferromagnetic coupling between the in-plane component of the magnetization of the antiferromagnetic coupling auxiliary layer 160 and the in-plane component of the ferromagnetic oscillation layer 140 to increase the tilt angle of the magnetization of the ferromagnetic oscillation layer 140. During the precession of the magnetization of the spin-polarizing layer 120, the ferromagnetic oscillation layer 140, and the antiferromagnetic coupling assist layer 160, the in-plane component of the magnetization of the antiferromagnetic coupling assist layer 160 and the in-plane component of the ferromagnetic oscillation layer 140 remain locked into antiferromagnetic alignment (i.e., 180 degrees out of azimuth angle).
Fig. 5 illustrates a second exemplary spin torque oscillator 500 according to a second embodiment of the present disclosure. The second exemplary STO 500 includes the same device layer stack 111 as described above with respect to the first exemplary STO 100. Accordingly, the device layer stack 111 layers will not be described again for the sake of brevity. The second exemplary STO 500 does not include the electromagnet 240 of the first embodiment. In contrast, second exemplary STO 500 includes at least one notch that generates a magnetic field, as will be described below.
The second exemplary STO 500 includes a first electrode 510 and a second electrode 590. The first electrode 510 includes a first ferromagnetic electrode layer 510L and a first ferromagnetic pillar 510P protruding from the first ferromagnetic electrode layer 510L toward the device layer stack 111. The second electrode 590 includes a second ferromagnetic electrode layer 590L and a second ferromagnetic pillar 590P protruding from the second ferromagnetic electrode layer 590L toward the device layer stack 111.
At least one of the first electrode 510 and/or the second electrode 590 includes a fixed ferromagnetic material having a fixed magnetization direction, such as Fe, co, ni, or an alloy thereof. In one embodiment, the fixed magnetization direction is parallel to the interface between the spin-polarized layer 120 and the nonmagnetic spacer layer 130. In one embodiment, the first electrode 510 and/or the second electrode 590 may comprise a pinned soft magnetic material or a hard magnetic material. If the electrode comprises pinned soft magnetic material, it may also comprise a synthetic ferromagnetic Structure (SAF) comprising an antiferromagnetic pinning layer and a stack of ferromagnetic layers separated from the soft magnetic material by a conductive nonmagnetic spacer.
The first ferromagnetic pillar 510P has a lateral width (e.g., diameter) that is substantially the same as a lateral width (e.g., diameter) of the device layer stack 111. The lateral dimension (e.g., width) of the first electrode layer 510L is greater than the lateral dimension of the first ferromagnetic pillar 510P such that the annular horizontal surface 510S of the first ferromagnetic electrode layer 510L surrounds the base of the vertical first ferromagnetic pillar 510P. Accordingly, the first electrode 510 includes a notch 510N at the junction of the first ferromagnetic electrode layer 510L and the first ferromagnetic pillar 510P. When a current flows between the first electrode 510 and the second electrode 590, the annular horizontal surface 510S generates a stray magnetic field along the side surface of the first ferromagnetic pillar 510P. The vertical component of the stray magnetic field is applied to the layers of the device layer stack 111 and is used as the bias magnetic field in the first embodiment, rather than the bias magnetic field generated by the electromagnet 140. Preferably, the depth of the notch 510N is greater than its width to create a vertical stray magnetic field. The notch can also be used as a shield to stabilize the STO 500 frequency against external fields.
The second ferromagnetic pillar 590P has a lateral width (e.g., diameter) that is substantially the same as a lateral width (e.g., diameter) of the device layer stack 111. The lateral dimension (e.g., width) of the second ferromagnetic electrode layer 590L is greater than the lateral dimension of the second ferromagnetic column 590P such that the annular horizontal surface 590S of the second electrode layer 590L surrounds the base of the vertical second ferromagnetic column 590P. Accordingly, the second electrode 590 includes a notch 590N at the junction of the second ferromagnetic electrode layer 590L and the second ferromagnetic pillar 590P. When a current flows between the first electrode 510 and the second electrode 590, the annular horizontal surface 590S generates a stray magnetic field along the side surface of the second ferromagnetic pillar 590P. The vertical component of the stray magnetic field is applied to the layers of the device layer stack 111 and is used as a bias magnetic field in the second embodiment, rather than the bias magnetic field generated by the electromagnet 140. Preferably, the depth of the notch 590N is greater than its width to create a vertical stray magnetic field. The notch can also be used as a shield to stabilize the STO 500 frequency against external fields.
In one embodiment, the sidewalls of the layers of the device layer stack 111 vertically coincide with the sidewalls of the first ferromagnetic pillar 510 and/or the second ferromagnetic pillar 590P.
Referring to fig. 6, a third exemplary periodic signal generator according to a second embodiment of the present disclosure is shown. By replacing the example of the first exemplary spin torque oscillator 100, a second periodic signal generator can be derived from the first periodic signal generator of fig. 2.
Referring to fig. 7, a fourth exemplary periodic signal generator according to a second embodiment of the present disclosure is shown that may be derived from the third exemplary periodic signal generator of fig. 6 by connecting multiple instances (such as two or more instances) of the second exemplary spin torque oscillator 500 of fig. 5 in a parallel configuration.
Referring to fig. 8, alignment of magnetization of component layers within the device layer stack 111 in the second exemplary spin torque oscillator 500 in the presence of a dc bias spin current is shown in accordance with a second embodiment of the present disclosure. A dc bias voltage may be applied between the first electrode and the second electrode (510,590) by the control circuit 305. The one or more notches (510 n, 630 n) generate a magnetic field having a vertical direction antiparallel to the direction of the spin current, while the electromagnet 240 may be omitted. The magnetic field acts similarly to the external magnetic field generated by the electromagnet 240 of the first embodiment for precessing the magnetization of the layers of the device layer stack 111 in a manner similar to the first embodiment described above with reference to fig. 4C.
Referring to fig. 9, a parallel connection of two second exemplary spin torque oscillators 500 according to a second embodiment of the present invention is shown. In this case, each first electrode layer 510L of the plurality of instances of the second exemplary spin torque oscillator 500 includes a respective portion of the common first electrode layer 510L, and each second electrode layer 590L of the plurality of instances of the second exemplary spin torque oscillator 500 includes a respective portion of the common second electrode layer 590L.
The spin torque oscillator of embodiments of the present disclosure may be used for microwave signal generation in a cellular telephone, communication device, acoustic analyzer, or other communication device. Synchronous precession of the in-plane components of the various ferromagnetic layers provides a narrow oscillation frequency width (e.g., voltage or power output detected from STO within the integration frequency) with high intensity. Thus, the spin torque oscillator of embodiments of the present disclosure can provide higher intensity and narrower frequency peaks (e.g., having a smaller half width at half maximum) than prior art STO's.
While specific preferred embodiments have been mentioned above, it will be understood that the present disclosure is not so limited. Those of ordinary skill in the art will recognize that various modifications may be made to the disclosed embodiments and that such modifications are intended to be within the scope of the present disclosure. Embodiments employing specific structures and/or configurations are shown in this disclosure, it should be understood that this disclosure may be practiced with any other compatible structures and/or configurations that are functionally equivalent, provided that such substitutions are not explicitly prohibited or otherwise deemed to be impossible by one of ordinary skill in the art. All publications, patent applications, and patents cited herein are incorporated by reference in their entirety.
Claims (18)
1. A spin torque oscillator, comprising:
A first electrode;
A second electrode;
A device layer stack between the first electrode and the second electrode, wherein the device layer stack comprises:
a spin-polarizing layer comprising a first ferromagnetic material;
an auxiliary layer comprising a third ferromagnetic material;
A ferromagnetic oscillation layer including a second ferromagnetic material between the spin-polarizing layer and the auxiliary layer;
A nonmagnetic spacer layer, the nonmagnetic spacer layer being located between the spin-polarizing layer and the ferromagnetic oscillating layer; and
A nonmagnetic coupling layer located between the ferromagnetic oscillating layer and the auxiliary layer, wherein the auxiliary layer is antiferromagnetically coupled to the ferromagnetic oscillating layer by the nonmagnetic coupling layer, and the auxiliary layer has a magnetization coupled to the magnetization of the ferromagnetic oscillating layer;
an electromagnet positioned adjacent to the device layer stack and configured to direct a bias magnetic field through the device layer stack; and
A control circuit configured to apply a bias voltage between the first electrode and the second electrode to induce a spin current between the first electrode and the second electrode that flows through the device layer stack,
Wherein:
The magnetization of the ferromagnetic oscillation layer is ferromagnetically coupled to the magnetization of the spin-polarized layer while the spin current does not flow through the device layer stack and the electromagnet is turned off, an
The magnetization of the ferromagnetic oscillation layer and the magnetization of the spin-polarizing layer are in-plane magnetizations parallel to an interface between the spin-polarizing layer and the nonmagnetic spacer layer, while the electromagnet is turned off and the spin current does not flow through the device layer stack.
2. The spin torque oscillator of claim 1, wherein the ferromagnetic oscillating layer has a larger magnetic moment-thickness product than the spin polarizing layer.
3. The spin torque oscillator of claim 2, wherein a ratio of a magnetic moment-thickness product of the ferromagnetic oscillation layer to a magnetic moment-thickness product of the spin-polarized layer is in a range of 1.2 to 5.
4. The spin torque oscillator of claim 2, wherein the auxiliary layer has a larger magnetic moment-thickness product than the ferromagnetic oscillating layer.
5. The spin torque oscillator of claim 4, wherein a ratio of a magnetic moment-thickness product of the auxiliary layer to a magnetic moment-thickness product of the ferromagnetic oscillating layer is in a range of 2 to 10.
6. The spin torque oscillator of claim 1, wherein the magnetization of the ferromagnetic oscillating layer and the magnetization of the spin polarizing layer are axial magnetizations parallel to the bias magnetic field while the electromagnet is turned on and the spin current does not flow through the device layer stack.
7. The spin torque oscillator of claim 6, wherein the magnetization of the spin-polarizing layer follows the magnetization of the ferromagnetic oscillating layer in an anti-parallel direction, while an azimuth angle of an in-plane component of the magnetization of the ferromagnetic oscillating layer is the same as an azimuth angle of the in-plane component of the magnetization of the spin-polarizing layer, while the electromagnet is turned on and the spin current flows through the device layer stack.
8. The spin torque oscillator of claim 7, wherein the magnetization of the ferromagnetic oscillating layer and the magnetization of the auxiliary layer are in-plane magnetizations that are antiparallel to each other and to an interface between the ferromagnetic oscillating layer and the nonmagnetic spacer layer while the electromagnet is turned off and the spin current does not flow through the device layer stack.
9. The spin torque oscillator of claim 8, wherein an axial component of magnetization of the ferromagnetic oscillating layer and an axial component of magnetization of the auxiliary layer are parallel to the bias magnetic field while the electromagnet is turned on and the spin current does not flow through the device layer stack.
10. The spin torque oscillator of claim 9, wherein:
The magnetization of the auxiliary layer is coupled to the magnetization of the ferromagnetic oscillating layer and precesses about a vertical axis at the same precession frequency as the magnetization of the spin-polarized layer, while the electromagnet is turned on and the spin current flows through the device layer stack; and
The azimuthal angle of the in-plane component of the magnetization of the ferromagnetic oscillating layer is offset 180 degrees relative to an azimuthal angle of the in-plane component of the magnetization of the auxiliary layer while the electromagnet is turned on and the spin current flows through the device layer stack.
11. The spin torque oscillator of claim 1, wherein:
The first ferromagnetic material of the spin-polarized layer comprises: fe, co, ni, ferromagnetic alloys comprising at least one of Fe, co or Ni, or magnetic heusler alloys;
the nonmagnetic spacer layer comprises a nonmagnetic metal, a semiconductor material, magnesium oxide, or aluminum oxide;
The second ferromagnetic material of the ferromagnetic oscillating layer includes: fe, co, ni, ferromagnetic alloys comprising at least one of Fe, co or Ni, or magnetic heusler alloys;
the nonmagnetic coupling layer comprises ruthenium, rhodium or iridium; and
The third ferromagnetic material of the auxiliary layer comprises: fe, co, ni, ferromagnetic alloys comprising at least one of Fe, co or Ni, or magnetic heusler alloys.
12. The spin torque oscillator of claim 11, wherein:
the spin-polarized layer has a thickness in the range of 1nm to 3 nm;
the thickness of the nonmagnetic spacer layer is in the range of 0.8nm to 3 nm;
the thickness of the ferromagnetic oscillation layer is in the range of 2nm to 15 nm;
The thickness of the non-magnetic coupling layer is in the range of 0.4nm to 2 nm; and
The thickness of the auxiliary layer is in the range of 2nm to 100 nm.
13. A periodic signal generator comprising:
At least one spin torque oscillator according to claim 1; and
A signal amplifier circuit configured to output a microwave signal having a frequency in a range of 2GHz to 100 GHz.
14. The periodic signal generator of claim 13, further comprising a plurality of the spin torque oscillators configured in parallel.
15. A method of operating a spin torque oscillator, the spin torque oscillator comprising:
A first electrode;
A second electrode;
A device layer stack between the first electrode and the second electrode, wherein the device layer stack comprises:
a spin-polarizing layer comprising a first ferromagnetic material;
an auxiliary layer comprising a third ferromagnetic material;
A ferromagnetic oscillation layer including a second ferromagnetic material between the spin-polarizing layer and the auxiliary layer;
A nonmagnetic spacer layer, the nonmagnetic spacer layer being located between the spin-polarizing layer and the ferromagnetic oscillating layer; and
A nonmagnetic coupling layer located between the ferromagnetic oscillating layer and the auxiliary layer, wherein the auxiliary layer is antiferromagnetically coupled to the ferromagnetic oscillating layer by the nonmagnetic coupling layer, and the auxiliary layer has a magnetization coupled to the magnetization of the ferromagnetic oscillating layer; and
An electromagnet positioned adjacent to the device layer stack and configured to direct a bias magnetic field through the device layer stack;
The method comprises the following steps:
the electromagnet is turned on to generate a bias magnetic field without flowing a spin current through the device layer stack such that magnetization of the ferromagnetic oscillating layer, magnetization of the spin-polarizing layer, and magnetization of the auxiliary layer are axial magnetizations parallel to a direction of the bias magnetic field.
16. The method of claim 15, further comprising flowing the spin current through the device layer stack while turning on the electromagnet such that:
The magnetization of the spin-polarizing layer follows the magnetization of the ferromagnetic oscillating layer in an antiparallel direction, while an azimuth angle of an in-plane component of the magnetization of the ferromagnetic oscillating layer is the same as an azimuth angle of the in-plane component of the magnetization of the spin-polarizing layer;
The magnetization of the auxiliary layer is coupled to the magnetization of the ferromagnetic oscillating layer and precesses about a vertical axis at the same precession frequency as the magnetization of the spin-polarized layer; and
The azimuthal angle of the in-plane component of the magnetization of the ferromagnetic oscillating layer is offset 180 degrees relative to an azimuthal angle of the in-plane component of the magnetization of the auxiliary layer.
17. The method of claim 16, further comprising switching off the electromagnet and the spin current such that:
The magnetization of the ferromagnetic oscillation layer is ferromagnetically coupled to the magnetization of the spin-polarized layer, and the magnetization of the ferromagnetic oscillation layer and the magnetization of the spin-polarized layer are in-plane magnetizations parallel to an interface between the spin-polarized layer and the nonmagnetic spacer layer; and
The magnetization of the ferromagnetic oscillating layer and the magnetization of the auxiliary layer are in-plane magnetizations antiparallel to each other and to an interface between the ferromagnetic oscillating layer and the nonmagnetic spacer layer.
18. The method of claim 16, further comprising providing a microwave signal from the spin torque oscillator to a communication device.
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| US16/887,563 US11171605B1 (en) | 2020-05-29 | 2020-05-29 | Spin torque oscillator with an antiferromagnetically coupled assist layer and methods of operating the same |
| US16/887,563 | 2020-05-29 | ||
| US16/887,715 | 2020-05-29 | ||
| US16/887,715 US11239016B2 (en) | 2020-05-29 | 2020-05-29 | Spin torque oscillator with an antiferromagnetically coupled assist layer and methods of operating the same |
| PCT/US2020/067638 WO2021242323A1 (en) | 2020-05-29 | 2020-12-31 | Spin torque oscillator with an antiferromagnetically coupled assist layer and methods of operating the same |
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| US6040961A (en) * | 1997-10-27 | 2000-03-21 | International Business Machines Corporation | Current-pinned, current resettable soft AP-pinned spin valve sensor |
| FR2892871B1 (en) * | 2005-11-02 | 2007-11-23 | Commissariat Energie Atomique | SPEED POLARIZED ELELECTIC CURRENT FREQUENCY RADIO OSCILLATOR |
| FR2957210B1 (en) * | 2010-03-03 | 2012-04-13 | Commissariat Energie Atomique | RADIOFREQUENCY OSCILLATOR AND METHOD FOR GENERATING AN OSCILLATING SIGNAL |
| JP5892767B2 (en) * | 2011-10-28 | 2016-03-23 | 株式会社東芝 | Magnetic head, magnetic sensor, and magnetic recording / reproducing apparatus |
| US9595917B2 (en) * | 2015-08-05 | 2017-03-14 | Qualcomm Incorporated | Antiferromagnetically coupled spin-torque oscillator with hard perpendicular polarizer |
| JP2016006716A (en) * | 2015-10-15 | 2016-01-14 | 株式会社東芝 | Magnetic head, magnetic sensor and magnetic recording/reproducing device |
| US9966901B2 (en) * | 2015-11-19 | 2018-05-08 | Samsung Electronics Co., Ltd. | Spin-torque oscillator based on easy-cone anisotropy |
| CN109075210A (en) * | 2016-09-14 | 2018-12-21 | Tdk株式会社 | Magnetoresistance device and magnetoresistance module |
| CN110246959A (en) * | 2019-06-10 | 2019-09-17 | 深圳市思品科技有限公司 | A kind of microwave oscillator based on antiferromagnetic Skyrmion |
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