CN111312893A - Heterojunction material and preparation method and application thereof - Google Patents
Heterojunction material and preparation method and application thereof Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title abstract description 13
- 238000000151 deposition Methods 0.000 claims abstract description 102
- AMWRITDGCCNYAT-UHFFFAOYSA-L hydroxy(oxo)manganese;manganese Chemical compound [Mn].O[Mn]=O.O[Mn]=O AMWRITDGCCNYAT-UHFFFAOYSA-L 0.000 claims abstract description 76
- 230000008021 deposition Effects 0.000 claims abstract description 42
- 230000005291 magnetic effect Effects 0.000 claims abstract description 40
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- 229910002328 LaMnO3 Inorganic materials 0.000 claims description 28
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 28
- 239000001301 oxygen Substances 0.000 claims description 28
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- 239000013077 target material Substances 0.000 claims description 23
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- NUJOXMJBOLGQSY-UHFFFAOYSA-N manganese dioxide Inorganic materials O=[Mn]=O NUJOXMJBOLGQSY-UHFFFAOYSA-N 0.000 claims description 17
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 claims description 16
- 229910003369 La0.67Sr0.33MnO3 Inorganic materials 0.000 claims description 16
- 238000005245 sintering Methods 0.000 claims description 14
- 229910002367 SrTiO Inorganic materials 0.000 claims description 12
- HTXDPTMKBJXEOW-UHFFFAOYSA-N iridium(IV) oxide Inorganic materials O=[Ir]=O HTXDPTMKBJXEOW-UHFFFAOYSA-N 0.000 claims description 12
- 229910002370 SrTiO3 Inorganic materials 0.000 claims description 11
- 238000000137 annealing Methods 0.000 claims description 10
- 229910000473 manganese(VI) oxide Inorganic materials 0.000 claims description 10
- 229910000018 strontium carbonate Inorganic materials 0.000 claims description 10
- 238000009210 therapy by ultrasound Methods 0.000 claims description 10
- 229910002372 SrTiO3(001) Inorganic materials 0.000 claims description 8
- MRELNEQAGSRDBK-UHFFFAOYSA-N lanthanum oxide Inorganic materials [O-2].[O-2].[O-2].[La+3].[La+3] MRELNEQAGSRDBK-UHFFFAOYSA-N 0.000 claims description 8
- 239000002904 solvent Substances 0.000 claims description 8
- 238000003860 storage Methods 0.000 claims description 8
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- 238000000527 sonication Methods 0.000 claims description 6
- 238000001816 cooling Methods 0.000 claims description 5
- 238000004549 pulsed laser deposition Methods 0.000 claims description 4
- KTUFCUMIWABKDW-UHFFFAOYSA-N oxo(oxolanthaniooxy)lanthanum Chemical compound O=[La]O[La]=O KTUFCUMIWABKDW-UHFFFAOYSA-N 0.000 claims description 3
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- WAEMQWOKJMHJLA-UHFFFAOYSA-N Manganese(2+) Chemical compound [Mn+2] WAEMQWOKJMHJLA-UHFFFAOYSA-N 0.000 description 3
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- 230000003993 interaction Effects 0.000 description 3
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 description 3
- 229910001437 manganese ion Inorganic materials 0.000 description 3
- PPNAOCWZXJOHFK-UHFFFAOYSA-N manganese(2+);oxygen(2-) Chemical compound [O-2].[Mn+2] PPNAOCWZXJOHFK-UHFFFAOYSA-N 0.000 description 3
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- 229910002969 CaMnO3 Inorganic materials 0.000 description 1
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- 229910002244 LaAlO3 Inorganic materials 0.000 description 1
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- 230000005533 two-dimensional electron gas Effects 0.000 description 1
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Abstract
The invention provides a heterojunction material and a preparation method and application thereof. The heterojunction material comprises SrIrO3Layer and layer located in the SrIrO3A manganese oxide layer on the layer. The preparation method comprises the following steps: (1) deposition of SrIrO3A layer; (2) In SrIrO3And depositing a manganese oxide layer on the layer to obtain the heterojunction material. The heterojunction material provided by the invention has discontinuous polarity and SrIrO through a heterojunction interface3The asymmetric charge transfer of the heterojunction interface is driven under the combined action of medium-strong spin-orbit coupling energy. By adjusting the polarity discontinuity of the heterojunction interface and in conjunction with SrIrO3The medium and strong spin coupling energy can effectively regulate and control the degree of interface charge transfer, thereby realizing the adjustment of the magnetic coupling performance of the heterojunction material interface.
Description
Technical Field
The invention belongs to the technical field of functional materials, data storage materials and magnetic materials, and relates to a heterojunction material and a preparation method and application thereof.
Background
The synthesis of oxide heterojunction is one of the hot areas of the current design of novel functional materials. Oxide heterojunction interfaces exhibit many unique physical properties as compared to the bulk materials that make up the heterojunction, due to the strong interactions between charge, spin, orbital, and lattice degrees of freedom. Since 2001, the university of tokyo, k.s.takahashi, group of subjects studied CaRuO3(paramagnetic)/CaMnO3After charge transfer has been proposed in the problem of origin of ferromagnetic order at the (antiferromagnetic) heterojunction interface, it becomes a core problem in discussing the physical properties of the oxide heterojunction interface. Typically, charge transfer can be driven by a contact oxide work function difference or heterojunction interface polarity discontinuity. The best known model for polarity discontinuity-induced charge transfer is in the polarity LaAlO3And nonpolar SrTiO3A two-dimensional electron gas is formed at the heterojunction interface of the insulator. Also, peculiar physical phenomena such as insulation-metal transition and ferromagnetism occur at such a polar heterojunction interface. Therefore, many important interfacial physical properties in oxide heterojunctions can be effectively tuned by manipulating the polarity discontinuity of the interface.
Recently, 5d iridium-based transition group metal oxides having strong spin-orbit coupling energy have attracted extensive interest to researchers. Theoretical research finds that under the action of strong spin-orbit coupling energy, the 5d iridium-based transition metal oxide contains rich novel physical properties such as complexityMagnetic, Weyl semimetal, topological insulator, and the like. And SrIrO of perovskite structure3The heterojunction formed with the manganese oxide is an ideal platform for researching the interface magnetic coupling of the 3d/5d transition group metal oxide heterojunction. Experiments find that in SrMnO3(antiferromagnetic)/SrIrO3Ferromagnetic ground states and abnormal hall effects are observed at the (paramagnetic) heterojunction interface. Even if SrMnO3And SrIrO3Has a small difference in work function (4.99eV and 5.05eV) and the interface is non-polar, but due to SrIrO3The medium strong spin-orbit coupling and the interface d-orbit reconstruction still generate the charge transfer which changes the physical properties of the interface. Thus, the combined effect of exploiting polarity discontinuities and strong spin-orbit coupling may present challenges and opportunities for manipulation of transition group metal heterojunction interface physical properties, as well as a wide range of potential applications.
Exchange bias effect was first discovered in CoO shell covered Co particle systems by Meiklejohn and Been in 1956 as a typical phenomenon of interfacial magnetic coupling. The spin valve read head designed by the exchange bias effect can be applied to a magnetic disk drive to well improve the sensitivity of the read head in a magnetic storage device, so that the storage density and the performance of the magnetic disk are greatly improved. The exchange bias effect based on the interface magnetic coupling performance has important and wide application potential in the fields of high-density magnetic information storage, low-power consumption spintronic devices and the like, and therefore, the exchange bias effect is more and more attracted by people. It is generally believed that the exchange bias effect arises from the magnetic coupling effect at the ferromagnetic and antiferromagnetic interfaces, i.e., the pinning effect of the uncompensated magnetic moment of the antiferromagnetic interface on the ferromagnetic magnetic moment. However in some ferromagnetic/paramagnetic (LaNiO)3) The exchange bias effect is also observed in the thin film system of (a). Experiments show that interface charge transfer causes the valence state change of interface ions so as to change the magnetic behavior of the interface.
CN104947192A discloses a perovskite SrIrO3The preparation method of the single crystal thin film material comprises the following steps: s1: providing a perovskite type substrate; s2: cleaning the substrate; s3: annealing the substrate; s4: in the oxide molecular beam epitaxial system, Ir simple substance target evaporation source is adopted,A Sr elementary substance target evaporation source and an oxygen source, and epitaxially growing perovskite SrIrO on the surface of the substrate3A single crystal thin film material. But the product obtained by the method does not have the exchange bias effect.
Disclosure of Invention
In view of the above-mentioned shortcomings in the prior art, the present invention aims to provide a heterojunction material, and a preparation method and use thereof. The heterojunction material provided by the invention has strong exchange bias effect, and can be combined with SrIrO by changing the discontinuous polarity of the heterojunction interface3The moderately strong spin coupling can be used to tune the exchange bias field of the heterojunction, which can be used in a variety of applications.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a heterojunction material comprising SrIrO3Layer and layer located in the SrIrO3A manganese oxide layer on the layer.
The heterojunction material provided by the invention is paramagnetic SrIrO with a strong exchange bias effect3A base heterojunction thin film material. Such materials can be made by manipulating the heterojunction interface polarity discontinuity and in conjunction with SrIrO3The medium-strength spin coupling can regulate and control interface charge transfer so as to achieve the purpose of regulating the magnetic coupling performance of the heterojunction thin film interface, and the heterojunction thin film interface has wide application potential in the fields of magnetic information storage, magnetic sensors and the like.
The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.
In a preferred embodiment of the present invention, in the manganese oxide layer, the manganese oxide includes La0.67Sr0.33MnO3And/or LaMnO3。
In the present invention, La is used as manganese oxide0.67Sr0.33MnO3And/or LaMnO3Has the advantages that the two manganese oxides have different polarities, and the heterojunction interface can be regulated and controlledThe purpose of the polarity discontinuity.
Preferably, the manganese oxide is (001) oriented.
(001) Oriented La0.67Sr0.33MnO3Film composed of band +0.67e+Of [ La ]0.67Sr0.33O]Flour and ribbon-0.67 e-Electric [ MnO ]2]LaMnO of alternating composition of faces and (001) orientation3The film is made of charged LaO+1And MnO2 -1The two (001) oriented manganese oxide films exhibit different polarity characteristics with alternating composition, and therefore the two different polarity manganese oxides are selected to achieve control of heterojunction interface polarity discontinuity.
Preferably, the SrIrO3The thickness of the layer is 15-25nm, such as 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm or 25 nm.
In the present invention, if SrIrO3The layer thickness is too thick, which can lead to the stress of the film to be completely released, and the film has similar properties with the bulk; if SrIrO3Too thin a layer thickness can result in discontinuity in the film.
Preferably, the manganese oxide layer has a thickness of 5-15nm, such as 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, or the like.
In the present invention, if the thickness of the manganese oxide is too thick, a significant reduction in the exchange bias effect results (see examples 2-4); if the thickness of the manganese oxide is too thin, discontinuity of the film may be caused.
As a preferable technical scheme of the invention, the SrIrO3The layer is located on the substrate.
Preferably, the substrate is SrTiO3A substrate.
Preferably, the substrate is SrTiO3(001) A single crystal substrate. The substrate and the heterojunction material have high lattice parameter matching degree, and the lattice parameter mismatch rate is less than 1.4%.
In a second aspect, the present invention provides a method of preparing a heterojunction material as described in the first aspect, the method comprising the steps of:
(1) deposition of SrIrO3A layer;
(2) in step (1), the SrIrO3And depositing a manganese oxide layer on the layer to obtain the heterojunction material.
The method provided by the invention can control SrIrO by adjusting the material type of the manganese oxide layer and regulating and controlling the deposition time3Thickness of layer and manganese oxide layer to achieve polarity discontinuity to heterojunction interface and to SrIrO3And the degree of interface charge transfer is effectively regulated and controlled by regulating the medium-strength spin coupling energy, so that the interface magnetic coupling performance of the heterojunction thin film is regulated.
The method provided by the invention is simple and feasible, can be industrially popularized and has a certain application value in the field of information storage.
As a preferable technical scheme of the invention, the SrIrO is deposited in the step (1)3The method of layer comprises: deposition of SrIrO on a substrate using pulsed laser deposition3And (3) a layer.
Preferably, the laser energy of the laser deposition method is 0.8-1.5J/cm2E.g. 0.8J/cm2、0.9J/cm2、1J/cm2、1.1J/cm2、1.2J/cm2、1.3J/cm2、1.4J/cm2Or 1.5J/cm2And the like.
Preferably, the distance between the target and the substrate in the laser deposition method is 3-6cm, such as 3cm, 4cm, 5cm or 6 cm.
Preferably, the deposited SrIrO3Target for layer deposition of SrIrO3The target material of the layer is SrCO3And IrO2SrIrO obtained by sintering3. In particular, the deposited SrIrO3The target material of the layer is formed by mixing SrCO with purity higher than 99.99%3And IrO2The powder is obtained by weighing, proportioning, fully grinding and uniformly mixing the powder according to a proportion and sintering the powder by using a traditional solid-phase reaction method.
In the present invention, the SrIrO is deposited3The target material of the layer is prepared by sintering by using the traditional solid-phase reaction method, and SrCO required by target material sintering3And IrO2The purity of the powder is higher than 99.99 percent;
preferably, the deposited SrIrO3The deposition temperature of the layer is 650-750 deg.C, such as 650 deg.C, 660 deg.C, 670 deg.C, 680 deg.C, 690 deg.C, 700 deg.C, 710 deg.C, 720 deg.C, 730 deg.C, 740 deg.C or 750 deg.C.
In the present invention, if SrIrO is deposited3The deposition temperature of the layer is too high, so that Ir element is separated out; if SrIrO is deposited3The deposition temperature of the layer is too low, resulting in poor crystallinity of the film.
Preferably, the deposited SrIrO3Deposition oxygen pressure of layer 10-1-3.5×101Pa, for example, 0.1Pa, 0.5Pa, 1Pa, 5Pa, 10Pa, 15Pa, 20Pa, 25Pa, 30Pa, 35Pa, or the like.
As a preferable technical scheme of the invention, the substrate is SrTiO3A substrate. The substrate has high matching degree of lattice parameters with the heterojunction material and small mismatch rate of the lattice parameters.
Preferably, the SrTiO3The substrate is single-side polished SrTiO3(001) A single crystal substrate.
Preferably, the substrate is pre-treated prior to use.
Preferably, the pre-treatment comprises sonication.
Preferably, the method of sonication comprises: the substrate is sonicated in a first solvent for a first time, followed by a second time in a second solvent.
Preferably, the first solvent comprises isopropanol.
Preferably, the second solvent comprises water.
Preferably, the first time is 10-20min, such as 10min, 12min, 14min, 16min, 18min or 20min, etc.
Preferably, the second time is 3-8min, such as 3min, 4min, 5min, 6min, 7min or 8min, etc.
Preferably, the sonication is repeated 2-3 times during the pretreatment.
As a preferred embodiment of the present invention, the method for depositing a manganese oxide layer in step (2) includes: adopting a pulse laser deposition methodThe SrIrO in step (1)3A manganese oxide layer is deposited over the layer and annealed.
The purpose of the annealing here is to remove possible oxygen vacancies.
In a preferred embodiment of the present invention, in the manganese oxide layer, the manganese oxide includes La0.67Sr0.33MnO3And/or LaMnO3。
Preferably, in step (1), the SrIrO3Depositing La on the layer0.67Sr0.33MnO3The target material is La2O3、SrCO3And MnO2La obtained by sintering0.67Sr0.33MnO3. Specifically, the SrIrO3Depositing La on the layer0.67Sr0.33MnO3The target material is prepared by adding La with the purity higher than 99.99 percent2O3、SrCO3And MnO2The powder is obtained by weighing, proportioning, fully grinding and uniformly mixing the powder according to a proportion and sintering the powder by using a traditional solid-phase reaction method.
Preferably, in step (1), the SrIrO3Depositing LaMnO on the layer3The target material is La2O3And MnO2Sintering to obtain LaMnO3. Specifically, the SrIrO3Depositing LaMnO on the layer3The target material is prepared by adding La with the purity higher than 99.99 percent2O3And MnO2The powder is obtained by weighing, proportioning, fully grinding and uniformly mixing the powder according to a proportion and sintering the powder by using a traditional solid-phase reaction method.
The target material is prepared by sintering by using a traditional solid-phase reaction method, and La required by sintering of the target material2O3And MnO2The purity of the powder is higher than 99.99%.
The laser energy of the laser deposition method is 0.8-1.5J/cm2E.g. 0.8J/cm2、0.9J/cm2、1J/cm2、1.1J/cm2、1.2J/cm2、1.3J/cm2、1.4J/cm2Or 1.5J/cm2And the like.
Preferably, the distance between the target and the substrate in the laser deposition method is 3-6cm, such as 3cm, 4cm, 5cm or 6 cm.
Preferably, the deposition temperature for depositing the manganese oxide layer is 650-750 ℃, such as 650 ℃, 660 ℃, 670 ℃, 680 ℃, 690 ℃, 700 ℃, 710 ℃, 720 ℃, 730 ℃, 740 ℃ or 750 ℃ and the like.
Preferably, the deposited manganese oxide layer has a deposited oxygen pressure of 10-1-3.5×101Pa, for example, 0.1Pa, 0.5Pa, 1Pa, 5Pa, 10Pa, 15Pa, 20Pa, 25Pa, 30Pa, 35Pa, or the like.
Preferably, the annealing is performed at an oxygen pressure of 0.4-0.8bar, such as 0.4bar, 0.5bar, 0.6bar, 0.7bar, or 0.8bar, etc.
Preferably, the annealing temperature is 650-750 ℃, such as 650 ℃, 660 ℃, 670 ℃, 680 ℃, 690 ℃, 700 ℃, 710 ℃, 720 ℃, 730 ℃, 740 ℃ or 750 ℃ and the like.
Preferably, the annealing time is 20-40min, such as 20min, 25min, 30min, 35min or 40min, etc.
As a further preferable technical scheme of the preparation method, the method comprises the following steps:
(1) depositing the substrate by adopting a pulse laser deposition method at a deposition temperature of 650-750 ℃ and a deposition temperature of 10 DEG C-1-3.5×101Pa deposition oxygen pressure deposition of SrIrO3A layer;
wherein the laser energy of the laser deposition method is 0.8-1.5J/cm2The distance between the target material and the substrate of the laser deposition method is 3-6 cm;
the substrate is SrTiO with a polished single surface3(001) The single crystal substrate is pretreated before use, wherein the pretreatment comprises ultrasonic treatment in isopropanol for 10-20min, ultrasonic treatment in water for 3-8min and repeated ultrasonic treatment for 2-3 times;
(2) adopting a pulse laser deposition method to perform SrIrO in the step (1)3Depositing a layer at a deposition temperature of 650-750 ℃ and a deposition temperature of 10-1-3.5×101Depositing a manganese oxide layer by Pa deposition oxygen pressure, annealing for 20-40min at 0.4-0.8bar, and cooling to obtain the heterojunction material;
wherein the laser energy of the laser deposition methodIs 0.8-1.5J/cm2And the distance between the target and the substrate in the laser deposition method is 3-6 cm.
In a third aspect, the present invention provides a use of a heterojunction material as described in the first aspect in the field of magnetic information storage or in the field of magnetic sensors.
Compared with the prior art, the invention has the following beneficial effects:
(1) the heterojunction material provided by the invention has a strong exchange bias effect, and the heterojunction material has discontinuous polarity and SrIrO (strontium IrO) through a heterojunction interface3The asymmetric charge transfer of the heterojunction interface is driven under the combined action of medium-strong spin-orbit coupling energy. By adjusting the polarity discontinuity of the heterojunction interface and in conjunction with SrIrO3The medium and strong spin coupling energy can effectively regulate and control the degree of interface charge transfer, thereby realizing the adjustment of the magnetic coupling performance of the heterojunction material interface. The exchange bias field H of the heterojunction material provided by the inventionECan reach 432 Oe.
(2) The preparation method provided by the invention is simple and feasible, can be industrially popularized and has a certain application value in the field of information storage.
Drawings
FIG. 1 is a schematic structural diagram of a heterojunction material prepared in example 1;
FIG. 2 is a schematic diagram of interfacial charge transfer for the heterojunction material prepared in example 1, wherein (a) SrO/IrO2/LaO/MnO2Charge transfer schematic in interface configuration, (b) IrO2/SrO/MnO2Schematic diagram after charge transfer in a/LaO interface configuration, wherein the arrow in the diagram represents the charge transfer;
FIG. 3 shows the heterojunction material (SIO/LSMO in the figure) prepared in example 1 and SrIrO as reference3(symbol SIO in the drawing) and La0.67Sr0.33MnO3Single layer films (labeled LSMO in the figure) have a zero field cold hysteresis loop at 2K;
FIG. 4 is a hysteresis loop of the heterojunction material prepared in example 1 cooled from room temperature to 2K at zero field and a magnetic field of +/-4000Oe, with the inset being an enlarged view of the hysteresis loop in the low field region;
FIG. 5 is a hysteresis loop of the heterojunction material prepared in example 2 cooled from room temperature to 2K at zero field and a magnetic field of +/-4000Oe, with SrIrO as the inset3And LaMnO3A zero field cold hysteresis loop of a single layer film;
FIG. 6 is a hysteresis loop of the heterojunction material prepared in examples 3 and 4 cooled from room temperature to 2K at zero field and a magnetic field of +/-4000Oe (where 9nm corresponds to example 3 and 15nm corresponds to example 4);
FIG. 7 shows exchange bias field vs. LaMnO for heterojunction materials prepared in examples 2, 3 and 43The profile of the change in layer thickness (example 2 for a point with a thickness of 5nm, example 3 for a point with a thickness of 9nm and example 4 for a point with a thickness of 15 nm).
Detailed Description
In order to better illustrate the present invention and facilitate the understanding of the technical solutions of the present invention, the present invention is further described in detail below. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the claims.
The following are typical but non-limiting examples of the invention:
example 1
This example prepares a heterojunction material as follows:
(1) SrTiO with one side polished by ultrasonic wave3(001) The single crystal substrate is respectively treated by ultrasonic treatment in isopropanol for 15min and deionized water for 5min, and the process is repeated twice.
(2) Adopting pulsed laser deposition method at 650 deg.C and oxygen pressure of 0.18mbar with SrCO3And IrO2The powder is weighed and proportioned according to the proportion of Sr and Ir elements of 1:1, fully ground and uniformly mixed, and then sintered to obtain SrIrO3Is a target material. The distance between the target and the substrate is 5cm and is 1.2J/cm2Depositing for 6min under laser energy, and depositing on SrTiO3(001) Depositing SrIrO with thickness of 25nm on the substrate3And (3) a layer.
(3) Adopting pulse laser deposition method under oxygen pressure condition with deposition temperature of 700 deg.C and 35PaWith La2O3、SrCO3And MnO2The powder material is prepared by weighing La, Sr and Mn according to the element ratio of 0.67:0.33:1, fully grinding and mixing uniformly, and sintering to obtain La0.67Sr0.33MnO3The distance between the target material and the substrate is 5cm and is 1.2J/cm2(001) SrTiO polished on one side under laser energy3Single crystal substrate (for comparison), and SrIrO has been prepared in step (2)3SrTiO of thin film layer3Depositing La with thickness of 6nm on the single crystal substrate for 3min0.67Sr0.33MnO3And (3) a layer. After deposition, the sample was annealed in situ at 700 ℃ for 0.5h under an oxygen pressure of 0.6bar, and then cooled to room temperature within 3h to remove possible oxygen vacancies, resulting in the heterojunction material.
The heterojunction material provided by the embodiment comprises SrIrO with the thickness of 25nm3Layer and layer located in the SrIrO3(001) -oriented La with a thickness of 6nm on the layer0.67Sr0.33MnO3Layer of said SrIrO3Layer located on SrTiO3The structure of the substrate is schematically shown in FIG. 1.
In the heterojunction material provided in this example, La0.67Sr0.33MnO3The film exhibited polar stacking along the (001) growth direction, from band +0.67e+Of [ La ]0.67Sr0.33O]Flour and ribbon-0.67 e-Electric [ MnO ]2](001) -oriented SrIrO with alternate planes3From charge-neutral SrO and IrO2And (5) making the noodles. Thus, SrIrO in the (001) orientation3/La0.67Sr0.33MnO3The heterojunction interface creates a polarity discontinuity. Asymmetric charge transfer occurs at the heterojunction interface due to the interaction of the heterojunction interface charge polarity discontinuity with the molecular orbital coupling that accompanies the strong spin-orbit coupling.
FIG. 2 is a schematic diagram of charge transfer of the heterojunction material prepared in this example under different interface configurations, and it can be seen from FIG. 2 that due to the interaction of the discontinuity of heterojunction interface charge polarity and the molecular orbital coupling accompanied by strong spin-orbit coupling, the interface of the double-layer film is unpairedSo-called charge transfer. In the first case, the polarity-driven long-range charge transfer does not change the charge number of the interfacial Mn ion, but certainly increases the charge number of the interfacial iridium ion (see fig. 2 (a)). Then, from the J-1/2 energy level of the iridium ion to e of the manganese iongCharge transfer in the bonded state will reasonably increase the charge number of the interfacial manganese atom, as shown by the green arrow in fig. 2 (a). Thus, under the combined action of polarity-induced charge transfer and molecular orbital coupling and spin-orbit coupling driven charge transfer, charge is transferred from the J-1/2 energy level of the iridium ion to the e of the interfacial manganese iongThe number of bonding states will increase. In the second case, the charge transfer induced by polarity does not change the charge number of the interface manganese ion, but reduces the charge number of the interface iridium ion, and further reduces the orbital occupancy of the J-1/2 level, and also reduces the e of the interface manganese ion driven by molecular orbital coupling and spin-orbital couplinggCharge transfer in the bonded state. In both cases, the number of charges lost by the ions on one side of the interface is different from the amount of charges acquired by the ions on the other side.
For the SrIrO in the step (2)3Layer, step (3) Single side polished (001) SrTiO for comparison3La grown on single crystal substrate0.67Sr0.33MnO3The layer and the heterojunction material product obtained in the embodiment are characterized by magnetic performance by a superconducting quantum interferometer, the zero-field cold hysteresis loop of the layer at 2K is shown in figure 3, and the single-layer SrIrO3The film sample had paramagnetic properties, while La0.67Sr0.33MnO3Has single ferromagnetism and coercive force H at 2KCIs 25 Oe. However, for SrIrO3/La0.67Sr0.33MnO3The coercivity of the heterojunction thin film increased significantly to 1500Oe, which clearly indicates that there is strong interfacial exchange coupling in the heterojunction due to heterojunction interfacial charge transfer.
FIG. 4 is a hysteresis loop of the heterojunction material prepared in this example cooled from room temperature to 2K at zero field and a magnetic field of +/-4000Oe, wherein the inset is an enlarged view of the hysteresis loop in the low field region, from which it can be seen that the heterojunction passes through +4000Oe (-4000Oe)The hysteresis loop after field cooling is significantly shifted along the negative (positive) magnetic field axis, resulting in an exchange bias field of about-77 Oe (63 Oe). At the same time, the coercive force H of the field cooling magnetic hysteresis loopCAbout 1800Oe, which is significantly larger than the coercivity of the zero field cold hysteresis loop.
The SrIrO provided by the embodiment3(paramagnetic)/La0.67Sr0.33MnO3The presence of the unconventional exchange biasing effect in the (ferromagnetic) heterojunction thin film further confirms the strong interfacial exchange coupling effect in the heterojunction.
The SrIrO provided by the embodiment is processed by a superconducting quantum interferometer3/La0.67Sr0.33MnO3The heterojunction material is subjected to magnetic property characterization, and the exchange bias field H of the heterojunction material provided by the embodimentE＝77Oe。
Example 2
This example prepares a heterojunction material as follows:
(1) SrTiO with one side polished by ultrasonic wave3(001) The single crystal substrate is respectively treated by ultrasonic treatment in isopropanol for 15min and deionized water for 5min, and the process is repeated twice.
(2) Adopting pulsed laser deposition method at 650 deg.C and oxygen pressure of 0.18mbar with SrCO3And IrO2The powder is weighed and proportioned according to the proportion of Sr and Ir elements of 1:1, fully ground and uniformly mixed, and then sintered to obtain SrIrO3The distance between the target material and the substrate is 5cm and is 1.2J/cm2Depositing for 3.5min under laser energy, in SrTiO3(001) Depositing SrIrO with the thickness of 15nm on a substrate3And (3) a layer.
(3) Adopting pulse laser deposition method under the condition of oxygen pressure with deposition temperature of 700 ℃ and 35Pa, and using La2O3And MnO2The powder is weighed and proportioned according to the ratio of La to Mn of 1:1, fully ground and uniformly mixed, and sintered to obtain LaMnO3The distance between the target material and the substrate is 5cm and is 1.2J/cm2SrIrO has been prepared in step (2) under laser energy3SrTiO of thin film layer3Depositing LaMnO with a thickness of 5nm on the single crystal substrate for 3min3And (3) a layer. After deposition, the sample was annealed in situ at 700 ℃ for 0.5h under an oxygen pressure of 0.6bar, and then cooled to room temperature within 3h to remove possible oxygen vacancies, resulting in the heterojunction material.
The heterojunction material provided by the embodiment comprises SrIrO with the thickness of 15nm3Layer and layer located in the SrIrO3(001) oriented LaMnO with a thickness of 5nm on a layer3Layer of said SrIrO3Layer located on SrTiO3On a substrate. The present example provides a heterojunction material having a (001) plane of crystal orientation.
The SrIrO provided by the embodiment is processed by a superconducting quantum interferometer3/LaMnO3And (5) performing magnetic property characterization on the heterojunction material.
FIG. 5 shows the hysteresis loop of the heterojunction material prepared in this example cooled from room temperature to 2K under zero field and magnetic field of +/-4000Oe, with SrIrO as the insert3And LaMnO3The zero field cooling hysteresis loop of the single-layer film can be seen from the figure, the hysteresis loop of the heterojunction cooled by the magnetic field of +4000Oe is obviously shifted along the negative magnetic field axis, and a large exchange bias field of about 432Oe is obtained. Further, coercive force HC＝|HR-HLI/2 from LaMnO3The 315Oe of the monolayer film increased significantly to the 1722Oe of the bilayer film. Apparently due to the single layer of SrIrO3The film is paramagnetic, while the monolayer LaMnO3Does not exhibit any exchange biasing effect (see inset), and the exchange biasing effect observed in the heterojunction means that the heterojunction has a strong interfacial exchange coupling effect.
SrIrO provided in example 13/La0.67Sr0.33MnO3Compared with a heterojunction, the SrIrO provided by the embodiment3/LaMnO3The heterojunction film exhibits a larger exchange bias field (H)E432 Oe). This may be the maximum exchange bias field observed in paramagnetic/ferromagnetic systems in the data disclosed so far. This is mainly due to the (001) -oriented LaMnO3The film is made of charged LaO+1And MnO2 -1Alternating composition of faces, SrIrO is contemplated3/LaMnO3Polarity at the interfaceContinuity ratio SrIrO3/La0.67Sr0.33MnO3Much stronger polarity discontinuity at the interface, positively charged LaO+1The layer will spontaneously go to the adjacent neutral IrO2The layer contributes more electrons. Then, from the iridium ion J-1/2 state to e of manganese iongCharge transfer in the bonded state will reasonably increase the number of charges of the interfacial manganese ion. And SrIrO3/LaMnO3And SrIrO3/La0.67Sr0.33MnO3The difference in the degree of charge transfer at the interface is accompanied by a difference in the magnetic behavior.
Example 3
The preparation method of the heterojunction material of this example refers to example 2 except that the deposition time of step (3) is modified to 5.5min, so that LaMnO3The preparation method of example 2 was otherwise the same except that the thickness of the layer was 9 nm.
The structure of the heterojunction material provided by the embodiment is except for LaMnO3The other structural parameters were the same as for the product of example 2, except that the layer thickness was 9 nm.
The SrIrO provided by the embodiment is processed by a superconducting quantum interferometer3/LaMnO3The heterojunction material is subjected to magnetic property characterization, and the exchange bias field H of the heterojunction material provided by the embodimentE＝179Oe。
Example 4
The preparation method of the heterojunction material of this example refers to example 2 except that the deposition time of step (3) is modified to 9min, such that LaMnO3The preparation method of example 2 was otherwise the same except that the thickness of the layer was 15 nm.
The structure of the heterojunction material provided by the embodiment is except for LaMnO3The other structural parameters were the same as for the product of example 2, except that the layer thickness was 15 nm.
FIG. 6 is a hysteresis loop of the heterojunction materials prepared in examples 3 and 4 cooled from room temperature to 2K at zero field and a magnetic field of +/-4000Oe (where 9nm corresponds to example 3 and 15nm corresponds to example 4), and it can be seen from this graph that as LaMnO flows3The increase in layer thickness, the monotonic decrease in the exchange bias field, indicates a heterojunctionThe exchange bias effect is an interface phenomenon.
FIG. 7 shows exchange bias field vs. LaMnO for heterojunction materials prepared in examples 2, 3 and 43The profile of the change in layer thickness (example 2 for a point with a thickness of 5nm, example 3 for a point with a thickness of 9nm and example 4 for a point with a thickness of 15 nm) shows that the exchange bias effect decreases significantly with increasing film thickness. These results are similar to the results for the exchange bias effect in the antiferromagnetic/paramagnetic system, indicating that the exchange bias effect is SrIrO3/LaMnO3An interface exchange coupling phenomenon.
The SrIrO provided by the embodiment is processed by a superconducting quantum interferometer3/LaMnO3The heterojunction material is subjected to magnetic property characterization, and the exchange bias field H of the heterojunction material provided by the embodimentE＝80Oe。
Example 5
This example prepares a heterojunction material as follows:
(1) SrTiO with one side polished by ultrasonic wave3(001) The single crystal substrate is respectively treated by ultrasonic treatment in isopropanol for 10min and deionized water for 3min, and the process is repeated for 3 times.
(2) Adopting a pulse laser deposition method under the conditions of deposition temperature of 750 ℃ and oxygen pressure of 0.1Pa and using SrCO3And IrO2The powder is weighed and proportioned according to the proportion of Sr and Ir elements of 1:1, fully ground and uniformly mixed, and then sintered to obtain SrIrO3The distance between the target material and the substrate is 4cm and is 0.8J/cm2Depositing for 5min under laser energy, and depositing on SrTiO3(001) Depositing SrIrO with the thickness of 20nm on a substrate3And (3) a layer.
(3) Adopting pulse laser deposition method under the conditions of deposition temperature of 750 ℃ and oxygen pressure of 0.1Pa, and using La2O3And MnO2The powder is weighed and proportioned according to the ratio of La to Mn of 1:1, fully ground and uniformly mixed, and sintered to obtain LaMnO3The distance between the target material and the substrate is 3cm and is 0.8J/cm2SrIrO has been prepared in step (2) under laser energy3SrTiO of thin film layer3Depositing on the single crystal substrate for 2.5min,depositing LaMnO of 5nm thickness3And (3) a layer. After deposition is completed, the sample is annealed in situ at 750 ℃ for 40min under an oxygen pressure of 0.4bar, and then cooled to room temperature to remove possible oxygen vacancies, so as to obtain the heterojunction material.
The heterojunction material provided by the embodiment comprises SrIrO with the thickness of 20nm3Layer and layer located in the SrIrO3(001) oriented LaMnO with a thickness of 5nm on a layer3Layer of said SrIrO3Layer located on SrTiO3On a substrate.
The SrIrO provided by the embodiment is processed by a superconducting quantum interferometer3/LaMnO3The heterojunction material is subjected to magnetic property characterization, and the exchange bias field H of the heterojunction material provided by the embodimentE314Oe, which is smaller than the exchange bias field of the heterojunction material in example 2, mainly due to the difference in crystalline quality of the heterojunction under different growth conditions, in this example the crystallinity of the heterojunction is relatively poor.
Example 6
This example prepares a heterojunction material as follows:
(1) SrTiO with one side polished by ultrasonic wave3(001) The single crystal substrate is respectively treated by ultrasonic treatment in isopropanol for 20min and deionized water for 8min, and the process is repeated for 2 times.
(2) Adopting a pulse laser deposition method and under the conditions of deposition temperature of 650 ℃ and oxygen pressure of 35Pa, adopting SrCO3And IrO2The powder is weighed and proportioned according to the proportion of Sr and Ir elements of 1:1, fully ground and uniformly mixed, and then sintered to obtain SrIrO3The distance between the target material and the substrate is 6cm and is 1.5J/cm2Depositing for 5.5min under laser energy, in SrTiO3(001) Depositing SrIrO with the thickness of 20nm on a substrate3And (3) a layer.
(3) Adopting pulse laser deposition method under the condition of oxygen pressure with deposition temperature of 650 ℃ and 30Pa, and using La2O3And MnO2The powder is weighed and proportioned according to the ratio of La to Mn of 1:1, fully ground and uniformly mixed, and sintered to obtain LaMnO3The distance between the target material and the substrate is 6cm and is 1.5J/cm2Under laser energy, in step (2)Has prepared SrIrO3SrTiO of thin film layer3Depositing LaMnO with a thickness of 5nm on the single crystal substrate for 4min3And (3) a layer. After deposition is completed, the sample is annealed in situ at 650 ℃ for 20min under an oxygen pressure of 0.8bar, and then cooled to room temperature to remove possible oxygen vacancies, so as to obtain the heterojunction material.
The heterojunction material provided by the embodiment comprises SrIrO with the thickness of 20nm3Layer and layer located in the SrIrO3(001) oriented LaMnO with a thickness of 5nm on a layer3Layer of said SrIrO3Layer located on SrTiO3On a substrate.
The SrIrO provided by the embodiment is processed by a superconducting quantum interferometer3/LaMnO3The heterojunction material is subjected to magnetic property characterization, and the exchange bias field H of the heterojunction material provided by the embodimentE230Oe, which is smaller than the exchange bias field of the heterojunction material in example 2, is mainly due to the difference in crystalline quality of the heterojunction under different growth conditions, which is relatively poor in this example.
In summary, the heterojunction material provided by the invention has discontinuous polarity and SrIrO through the heterojunction interface3The asymmetric charge transfer of the heterojunction interface is driven under the combined action of medium-strong spin-orbit coupling energy. The heterojunction material provided by the invention can effectively regulate and control the degree of interface charge transfer, thereby realizing the regulation of the magnetic coupling performance of the heterojunction material interface.
From a comparison of example 1 and example 2, it can be seen that LaMnO was used3As manganese oxide material, La is used0.67Sr0.33MnO3With a larger exchange bias field.
As can be seen from the comparison of examples 2, 3 and 4, the thickness of the exchange bias field can be effectively adjusted by adjusting the thickness of the manganese oxide layer, and the exchange bias effect is obviously reduced as the thickness of the manganese oxide film is increased.
The applicant states that the present invention is illustrated by the above examples to show the detailed process equipment and process flow of the present invention, but the present invention is not limited to the above detailed process equipment and process flow, i.e. it does not mean that the present invention must rely on the above detailed process equipment and process flow to be implemented. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
Claims (10)
1. A heterojunction material, wherein said heterojunction material comprises SrIrO3Layer and layer located in the SrIrO3A manganese oxide layer on the layer.
2. A heterojunction material according to claim 1, wherein in said manganese oxide layer, the manganese oxide comprises La0.67Sr0.33MnO3And/or LaMnO3；
Preferably, the manganese oxide is (001) oriented;
preferably, the SrIrO3The thickness of the layer is 15-25 nm;
preferably, the thickness of the manganese oxide layer is 5-15 nm.
3. A heterojunction material according to claim 1 or 2, wherein the SrIrO3The layer is located on the substrate;
preferably, the substrate is SrTiO3A substrate;
preferably, the substrate is SrTiO3(001) A single crystal substrate.
4. A method of preparing a heterojunction material as claimed in claim 1 or 2, wherein said method comprises the steps of:
(1) deposition of SrIrO3A layer;
(2) in step (1), the SrIrO3And depositing a manganese oxide layer on the layer to obtain the heterojunction material.
5. The method for producing according to claim 4, which isCharacterized in that the SrIrO is deposited in the step (1)3The method of layer comprises: deposition of SrIrO on a substrate using pulsed laser deposition3A layer;
preferably, the laser energy of the laser deposition method is 0.8-1.5J/cm2；
Preferably, the distance between the target and the substrate of the laser deposition method is 3-6 cm;
preferably, the deposited SrIrO3The target material of the layer is SrCO3And IrO2SrIrO obtained by sintering3；
Preferably, the deposited SrIrO3The deposition temperature of the layer is 650-750 ℃;
preferably, the deposited SrIrO3Deposition oxygen pressure of layer 10-1-3.5×101Pa。
6. The method according to claim 5, wherein the substrate is SrTiO3A substrate;
preferably, the SrTiO3The substrate is single-side polished SrTiO3(001) A single crystal substrate;
preferably, the substrate is pre-treated prior to use;
preferably, the pre-treatment comprises sonication;
preferably, the method of sonication comprises: sonicating the substrate in a first solvent for a first time followed by a second time in a second solvent;
preferably, the first solvent comprises isopropanol;
preferably, the second solvent comprises water;
preferably, the first time is 10-20 min;
preferably, the second time is 3-8 min;
preferably, the sonication is repeated 2-3 times during the pretreatment.
7. The method according to any one of claims 4 to 6, wherein the deposited manganese oxide of step (2)The method of layer comprises: adopting a pulse laser deposition method to perform SrIrO in the step (1)3A manganese oxide layer is deposited over the layer and annealed.
8. The production method according to any one of claims 4 to 7, wherein, in the manganese oxide layer, the manganese oxide includes La0.67Sr0.33MnO3And/or LaMnO3；
Preferably, in step (1), the SrIrO3Depositing La on the layer0.67Sr0.33MnO3The target material is La2O3、SrCO3And MnO2La obtained by sintering0.67Sr0.33MnO3；
Preferably, in step (1), the SrIrO3Depositing LaMnO on the layer3The target material is La2O3And MnO2Sintering to obtain LaMnO3；
The laser energy of the laser deposition method is 0.8-1.5J/cm2；
Preferably, the distance between the target and the substrate of the laser deposition method is 3-6 cm;
preferably, the deposition temperature for depositing the manganese oxide layer is 650-750 ℃;
preferably, the deposited manganese oxide layer has a deposited oxygen pressure of 10-1-3.5×101Pa；
Preferably, the annealing is performed at an oxygen pressure of 0.4-0.8 bar;
preferably, the temperature of the annealing is 650-750 ℃;
preferably, the annealing time is 20-40 min.
9. The method for preparing according to any one of claims 4 to 8, characterized in that it comprises the steps of:
(1) depositing the substrate by adopting a pulse laser deposition method at a deposition temperature of 650-750 ℃ and a deposition temperature of 10 DEG C-1-3.5×101Pa deposition oxygen pressure deposition of SrIrO3A layer;
wherein the laser of the laser deposition methodThe light energy is 0.8-1.5J/cm2The distance between the target material and the substrate of the laser deposition method is 3-6 cm;
the substrate is SrTiO with a polished single surface3(001) The single crystal substrate is pretreated before use, wherein the pretreatment comprises ultrasonic treatment in isopropanol for 10-20min, ultrasonic treatment in water for 3-8min and repeated ultrasonic treatment for 2-3 times;
(2) adopting a pulse laser deposition method to perform SrIrO in the step (1)3Depositing a layer at a deposition temperature of 650-750 ℃ and a deposition temperature of 10-1-3.5×101Depositing a manganese oxide layer by Pa deposition oxygen pressure, annealing for 20-40min at 0.4-0.8bar, and cooling to obtain the heterojunction material;
wherein the laser energy of the laser deposition method is 0.8-1.5J/cm2And the distance between the target and the substrate in the laser deposition method is 3-6 cm.
10. Use of a heterojunction material according to any of claims 1 to 3 in the field of magnetic information storage or in the field of magnetic sensors.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114242886A (en) * | 2021-11-30 | 2022-03-25 | 华中科技大学 | Method and device for regulating and controlling two-dimensional ferromagnetic/antiferromagnetic heterojunction exchange bias |
| CN114242886B (en) * | 2021-11-30 | 2024-05-14 | 华中科技大学 | Method and device for regulating and controlling two-dimensional ferromagnetic/antiferromagnetic heterojunction exchange bias |
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