JP2009070857A - Island-like magnetic thin film and manufacturing method thereof - Google Patents

Abstract

Kind Code: A1 A magnetic thin film made of a magnetic material containing a rare earth element has an island-like structure in which isolated island particles made of the magnetic material are arranged in a discontinuous film shape. Is an island-shaped magnetic thin film that is sufficiently small, has a sufficiently thin film thickness, and has a sufficiently high coercive force.
An island-like magnetic thin film in which isolated island particles made of a magnetic material are arranged in a discontinuous film shape, wherein the magnetic material contains a rare earth element, and has an in-plane diameter of the island particles. An island-shaped magnetic thin film characterized in that an average value is in a range of 40 to 140 nm and a thickness of the thin film is in a range of 2 to 25 nm.
[Selection figure] None

Description

  The present invention relates to an island-shaped magnetic thin film and a manufacturing method thereof.

  Conventionally, ultra-high density magnetic media capable of processing and storing large amounts of information have been developed, and research on various magnetic thin films that can be used for such magnetic media has been advanced. I came. For example, an FePt thin film is known as such a magnetic thin film. As a method for producing such a magnetic thin film, Japanese Patent Application Laid-Open No. 2003-289005 (Patent Document 1) has a magnetically isolated fine particle structure and is unidirectional. A method for producing a highly oriented magnetic thin film oriented in the form of an alloy thin film of at least one metal of Fe and Co and at least one metal of Pt and Pd having a surface temperature of 650. A method of forming a sputtering film on a substrate that is at or above ° C is known. In recent years, among such magnetic thin films, research on magnetic thin films using magnetic materials (permanent magnet materials) containing rare earth elements such as neodymium has been promoted.

  As a method for manufacturing a thin film using such a magnetic material containing a rare earth element, for example, after sputtering a magnetic material made of NdFeB on a molybdenum layer formed on a Si (100) substrate, 450 ° C. to 675 ° C. A method for producing a magnetic thin film that is annealed in a temperature range of 30 ° C. for 30 minutes is known (TVKhoa, NDHa, S. MHong et al., “Composition dependence of crystallization temperature and Magnetic property of NdFeB thin films”, Journal of Magnetism and Magnetic Materials, 2006, vol. 304, pages 246 to 248 (Non-patent Document 1)). Further, a method of forming a magnetic thin film by sputtering a magnetic material made of NdFeB on a molybdenum layer formed on a Si (100) substrate while heating the surface temperature of the substrate to 575 ° C. is known. (SLChen, W. Liu, ZDZhang et al., “Microstructure and magnetic properties of anisotropic Nd-Fe-B thin films fabricated with different deposition rates”, Journal of Magnetism and Magnetic Materials, 2006, vol. 302, 306 -309 pages (refer nonpatent literature 2).

However, in the method for producing a magnetic thin film as described in Non-Patent Document 1, a thin film made of a magnetic material containing a rare earth element cannot be made into an island structure. In addition, in the method of manufacturing a magnetic thin film as described in Non-Patent Document 2, the island particles formed are large even when the film thickness is large and an island-like structure is formed. An island-like structure composed of island particles with a small particle size could not be formed. In addition, in the method for producing a magnetic thin film as described in Non-Patent Document 1 or 2, since the rare earth element has a low oxidation resistance and a complicated crystal structure, the thickness is sufficiently thin and sufficiently high. A magnetic thin film having a coercive force could not be produced.
JP 2003-289005 A TVKhoa, NDHa, S. MHong et al., “Composition dependence of crystallization temperature and Magnetic property of NdFeB thin films”, Journal of Magnetism and Magnetic Materials, 2006, vol. 304, pages 246-248 SLChen, W. Liu, ZDZhang et al., “Microstructure and magnetic properties of anisotropic Nd-Fe-B thin films fabricated with different deposition rates”, Journal of Magnetism and Magnetic Materials, 2006, vol. 302, 306-309

  The present invention has been made in view of the above-described problems of the prior art, and is a magnetic thin film made of a magnetic material containing a rare earth element, in which isolated island particles made of the magnetic material are arranged in a discontinuous film shape. An island-like magnetic thin film having a sufficiently small coercive force, and a method of manufacturing the island-like magnetic thin film, wherein the island-shaped structure is formed, the island particles have a sufficiently small particle size, and the film thickness is sufficiently thin. The purpose is to provide.

  As a result of intensive studies to achieve the above object, the present inventors have formed an island-shaped thin film in which isolated island particles made of a magnetic material containing a rare earth element are arranged in a discontinuous film shape, It has been found that the above object can be achieved by setting the average value of the in-plane diameter of the island particles in the range of 40 to 140 nm and the thickness of the thin film in the range of 2 to 25 nm. The invention has been completed.

  That is, the island-shaped magnetic thin film of the present invention is an island-shaped magnetic thin film in which isolated island particles made of a magnetic material are arranged in a discontinuous film shape, and the magnetic material contains a rare earth element, The average value of the in-plane diameter of the island particles is in the range of 40 to 140 nm, and the thickness of the thin film is in the range of 2 to 25 nm.

  The magnetic material according to the present invention preferably contains neodymium, and more preferably contains neodymium, iron and boron.

  In the island-shaped magnetic thin film of the present invention, it is preferable that the average value of the distance between the nearest points of the island particles is in the range of 10 to 100 nm.

  Furthermore, in the island-shaped magnetic thin film of the present invention, the crystal phase of the magnetic material in the island particles is preferably c-plane oriented.

The method for manufacturing an island-shaped magnetic thin film according to the present invention is for forming a magnetic thin film by forming a base layer made of a base material containing at least one of molybdenum and tantalum on a substrate made of a magnesium oxide single crystal. Obtaining a substrate;
By sputtering a target material containing neodymium, iron and boron while maintaining the surface temperature of the magnetic thin film forming substrate at 590 ° C. to 670 ° C.,
Isolated island particles made of a magnetic material containing neodymium, iron and boron are arranged in a discontinuous film shape, and the crystal phase of the magnetic material in the island particles is c-plane oriented, and the island particles Forming an island-shaped magnetic thin film having an average in-plane diameter of 40 to 140 nm and a thickness of 2 to 25 nm on the underlayer;
It is the method characterized by including.

  Furthermore, in the method for producing an island-shaped magnetic thin film of the present invention, it is preferable that the deposition rate of the magnetic thin film by the sputtering is 1 Å / s or less.

  According to the present invention, a magnetic thin film made of a magnetic material containing a rare earth element is formed, and an island-like structure is formed in which isolated island particles made of the magnetic material are arranged in a discontinuous film shape. It is possible to provide an island-like magnetic thin film capable of having a sufficiently small particle size, a sufficiently thin film thickness, and a sufficiently high coercive force, and a method for manufacturing the same.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

  First, the island-shaped magnetic thin film of the present invention will be described. That is, the island-shaped magnetic thin film of the present invention is an island-shaped magnetic thin film in which isolated island particles made of a magnetic material are arranged in a discontinuous film shape, and the magnetic material contains a rare earth element, The average value of the in-plane diameter of the island particles is in the range of 40 to 140 nm, and the thickness of the thin film is in the range of 2 to 25 nm.

  Such island particles have an average in-plane diameter in the range of 40 to 140 nm. When the average value of the in-plane diameters of such island particles is less than the lower limit, it is difficult to form a crystal of the magnetic material (form crystal structure), and when the upper limit is exceeded, the magnetic continuity is increased and maintained. Magnetic force decreases. The “in-plane diameter” as used herein refers to the diameter of the shape of the island particles on the surface of the substrate or the like on which the island particles are arranged (the shape of the surface of the island particles in contact with the surface of the substrate or the like). If the shape is not circular, it refers to the maximum diameter of the circumscribed circle. In addition, such “in-plane diameter” is obtained by observing the state of the cross section of the thin film while selecting the energy of a specific component by TEM-EELS, and determining the size of each island particle from the TEM photograph of the obtained thin film. Can be measured.

  Moreover, it is preferable that it is in the range of 10-100 nm as an average value of the distance (separation distance of an island particle) between the closest points of such closest particles of an island particle. When the average value of such a separation distance is less than the lower limit, the magnetic continuity tends to be high and the coercive force tends to decrease.On the other hand, when the upper limit is exceeded, the volume fraction of the in-plane magnetic thin film is reduced. It tends to decrease and the magnetization decreases.

  The island-shaped magnetic thin film of the present invention has a structure (island-shaped structure) in which the isolated island particles made of a magnetic material are arranged in a discontinuous film shape. As such an island-shaped structure, the average value of the distance between the closest particles is 10 to 100 nm with island particles having an average in-plane diameter in the range of 40 to 140 nm isolated from each other. It is more preferable that the structure be arranged in a discontinuous film. In the island-shaped magnetic thin film of the present invention, since the island-shaped structure is formed by the fine island-shaped particles as described above, the magnetic continuity of the thin film is low and a sufficiently high coercive force can be exhibited. Is possible.

  Furthermore, the island-like magnetic thin film of the present invention has a thickness of 2 to 25 nm. When the thickness of such a thin film exceeds the upper limit, the magnetic thin film becomes a continuous film, and when the thickness is less than the lower limit, it is difficult to form a crystal of the magnetic material (form crystal structure). The “thickness of the thin film” referred to here is a value obtained by the product of the film formation speed and the film formation time.

The magnetic material forming such island particles is a material (crystal) containing a rare earth element and having magnetism. Here, the “material having magnetism” refers to a material having a high coercive force when a thin film having the island-like structure is formed from such a material. For example, in a thin film made of neodymium, iron, and boron. Means having an Nd ₂ Fe ₁₄ B structure. In addition, examples of the “rare earth element” in the present invention include neodymium, samarium, dysprosium, terbium, praseodymium, and holmium. Moreover, as long as such a magnetic material contains a rare earth element, other elements contained in the magnetic material are not particularly limited. Examples of such a rare earth element-containing magnetic material include a samarium-cobalt magnetic material containing samarium and cobalt, and a neodymium-iron-boron magnetic material (Fe—) containing neodymium, iron and boron. Examples thereof include magnetic materials containing known rare earth elements such as Nd—B magnetic materials. Further, as such a magnetic material, a magnetic material containing neodymium as a rare earth element is preferable from the viewpoint of having a high magnetocrystalline anisotropy, and among them, a magnetic material containing neodymium, iron and boron (particularly preferably) Nd ₂ Fe ₁₄ B) is more preferred.

  In the island particles, the crystal phase of the magnetic material in the island particles is preferably c-plane oriented. That is, as the island particles, the c-axis of the crystal of the magnetic material in the island particles is in the crystal growth direction (a direction perpendicular to the surface of the substrate when the island particles are arranged on the substrate). It is preferably oriented. Thus, since the crystal phase of the magnetic material is c-plane oriented, anisotropy appears in the magnetic characteristics.

  The island-shaped magnetic thin film of the present invention may be used by being arranged on various substrates. And as a board | substrate which arrange | positions the said island particle | grain, a MgO single crystal substrate is preferable. Further, when such an MgO single crystal substrate is used, a base layer made of a base material containing at least one of molybdenum and tantalum is formed on the MgO single crystal substrate, and the island layer is formed on the base layer. It is preferable that the particles are arranged. In addition, by using the MgO single crystal substrate on which such an underlayer is formed, it becomes possible to arrange the island particles in a discontinuous film shape (form the island-like structure) more efficiently during manufacturing. There is a tendency. Furthermore, it is preferable to arrange a protective film on the surface of such an island-shaped magnetic thin film from the viewpoint of preventing oxidation. The material for such a protective film is not particularly limited, and a known protective film material that can be laminated on the surface of the magnetic thin film to protect the magnetic thin film can be appropriately used. For prevention, chromium or the like may be used. Therefore, when the island-shaped magnetic thin film of the present invention is used, it is preferable to use the underlayer / island-shaped magnetic thin film / protective film sequentially laminated on the MgO single crystal substrate.

  Although the island-shaped magnetic thin film of the present invention has been described above, the method for manufacturing the island-shaped magnetic thin film of the present invention will be described below. In addition, the method for producing the island-shaped magnetic thin film of the present invention is a method for producing an island-shaped magnetic thin film made of a magnetic material containing neodymium, iron, and boron suitable as the island-shaped magnetic thin film of the present invention. This is a method that can be suitably employed.

According to the method for manufacturing an island-shaped magnetic thin film of the present invention, a magnetic thin film forming substrate is formed by forming a base layer made of a base material containing at least one of molybdenum and tantalum on a substrate made of a magnesium oxide single crystal. Obtaining step (A);
By sputtering a target material containing neodymium, iron and boron while maintaining the surface temperature of the magnetic thin film forming substrate at 590 ° C. to 670 ° C.,
Isolated island particles made of a magnetic material containing neodymium, iron and boron are arranged in a discontinuous film shape, and the crystal phase of the magnetic material in the island particles is c-plane oriented, and the island particles A step (B) of forming an island-shaped magnetic thin film having an average in-plane diameter of 40 to 140 nm and a thickness of 2 to 25 nm on the underlayer;
It is the method characterized by including. Hereinafter, steps (A) and (B) will be described separately.

  First, the step (A) will be described. Step (A) is a step of obtaining a magnetic thin film forming substrate by forming a base layer made of a base material containing at least one of molybdenum and tantalum on a substrate made of a magnesium oxide single crystal.

  The substrate used in the present invention is a substrate made of a magnesium oxide single crystal (hereinafter, simply referred to as “MgO substrate” in some cases). The substrate made of such a magnesium oxide single crystal is not particularly limited, and a commercially available product may be used. In addition, in a substrate made of such a magnesium oxide single crystal, it is preferable to use the (100) plane of the magnesium oxide single crystal from the viewpoint of c-plane orientation of the magnetic material in the island particles to be formed.

In the present invention, the base material used for forming the base layer contains at least one of molybdenum and tantalum. Such molybdenum (Mo) or tantalum (Ta) is a body-centered cubic (bcc) material having high lattice matching with the c-plane of a magnetic material (particularly preferably Nd ₂ Fe ₁₄ B). Then, by using the MgO substrate and forming the base layer made of the base material on the MgO substrate, the island particles of the magnetic material (particularly preferably Nd ₂ Fe ₁₄ B) with the c-plane orientation are efficiently formed. It becomes possible.

  In addition, the method for forming such a base layer is not particularly limited, and a method of forming a film by sputtering the base material on an MgO substrate can be suitably employed. Such sputtering conditions are not particularly limited, and known conditions can be appropriately employed.

  Further, the thickness of such an underlayer is not particularly limited and can be changed as appropriate. In addition, as such a base layer, the base material is preferably (001) -oriented. Thus, when the underlayer is (001) oriented, the crystal phase of the magnetic material in the island particles tends to be efficiently c-plane oriented.

Next, the step (B) will be described. The step (B) is performed by sputtering a target material containing neodymium, iron and boron while maintaining the surface temperature of the magnetic thin film forming substrate at 590 ° C. to 670 ° C.
Isolated island particles made of a magnetic material containing neodymium, iron and boron are arranged in a discontinuous film shape, and the crystal phase of the magnetic material in the island particles is c-plane oriented, and the island particles In this step, an island-shaped magnetic thin film having an average in-plane diameter of 40 to 140 nm and a thickness of 2 to 25 nm is formed on the underlayer.

In such a step (B), the surface temperature of the magnetic thin film forming substrate is maintained at 590 ° C. to 670 ° C. (more preferably 600 ° C. to 650 ° C.) during sputtering. When the surface temperature is lower than the lower limit, a continuous film is formed when the target material is supported by sputtering. On the other hand, if the surface temperature exceeds the upper limit, when the target material is sputtered, an island structure is formed, but no Nd ₂ Fe ₁₄ B phase is formed in the island particles, and the coercivity of the thin film obtained Is not enough.

  The target material used in the present invention contains neodymium (Nd), iron (Fe), and boron (B). The target material is not particularly limited as long as it can form island particles made of a magnetic material. For example, an alloy of Nd, Fe, and B (NdFeB alloy) whose composition is preliminarily prepared in advance. Etc. can be used as appropriate.

  Further, the sputtering method is not particularly limited, and a known sputtering method can be appropriately employed. For example, a magnetron sputtering method can be preferably employed. Moreover, the sputtering apparatus used for such sputtering is not particularly limited, and a known sputtering apparatus can be used as appropriate.

In addition, the film formation rate during sputtering is preferably 1 際 / s or less. Furthermore, in the sputtering, it is preferable that the degree of vacuum before film formation is 1 × 10 ⁻⁷ Pa or less. When the degree of vacuum exceeds the upper limit, the magnetic material is oxidized and the magnetic properties (coercive force) tend to decrease.

  In the sputtering, the island-shaped magnetic thin film is made to have a thickness in the range of 2 to 25 nm. If the thickness is less than the lower limit, it tends to be difficult to form a crystal of the magnetic material (form crystal structure). On the other hand, when the thickness exceeds the upper limit, the particle diameter of the formed island particles tends to increase, or a continuous film tends to be formed instead of an island-shaped film. Note that the thickness of such a thin film can be appropriately adjusted by adjusting the film formation speed and film formation time of sputtering.

  In the present invention, as described above, the island-like magnetic thin film formed by sputtering the target material while maintaining the surface temperature of the magnetic thin film forming substrate at 590 ° C. to 670 ° C. is neodymium and iron. Isolated island particles made of a magnetic material containing boron and boron are arranged in a discontinuous film shape, and the crystal phase of the magnetic material in the island particles is c-plane oriented, and the in-plane of the island particles The average diameter is in the range of 40 to 140 nm and the thickness is in the range of 2 to 25 nm.

The magnetic material forming such island particles contains Nd, Fe, and B. Such a magnetic material is particularly preferably an Nd ₂ Fe ₁₄ B crystal from the viewpoint that a sufficiently high coercive force can be obtained. Such a crystal of magnetic material is formed on the underlayer by sputtering the target material as described above.

  Moreover, in such island particles, the crystal phase of the magnetic material is c-plane oriented. That is, in the present invention, the c-axis of the crystal of the magnetic material in the island particles is oriented in the crystal growth direction (a direction perpendicular to the surface of the substrate when the island particles are arranged on the substrate). is doing. Such orientation of the crystal phase is achieved by using the magnetic thin film forming substrate formed in the step (A) and on the underlying layer of the substrate while maintaining the surface temperature of the magnetic thin film forming substrate in the above range. This is achieved by supporting the target material by sputtering as described above.

  The island particles formed by the sputtering have an average in-plane diameter in the range of 40 to 140 nm. Such island particles use the magnetic thin film forming substrate formed in the step (A), and maintain the surface temperature of the magnetic thin film forming substrate in the above range while on the underlayer of the substrate. The target material can be formed by sputtering and supporting it as described above.

  Further, the island-like magnetic thin film formed in this way has a thickness in the range of 2 to 25 nm. Further, the island-shaped magnetic thin film formed in this way has a structure (island-shaped structure) in which the isolated island particles are arranged in a discontinuous film shape. As such an island-shaped structure, the average value of the distance between the closest particles is 10 to 100 nm with island particles having an average in-plane diameter in the range of 40 to 140 nm isolated from each other. Thus, the structure is more preferably arranged in a discontinuous film shape. Such an island-shaped structure uses the magnetic thin film forming substrate formed in the step (A), and maintains the surface temperature of the magnetic thin film forming substrate in the above range as described above. The target material can be formed on the base layer of the substrate by sputtering.

  Further, after such an island-shaped magnetic thin film is formed, a protective film may be further formed. The material for such a protective film is not particularly limited, and a known protective film material that can be laminated on the surface of the magnetic thin film to protect the magnetic thin film can be appropriately used. For prevention, chromium or the like may be used. The method for forming such a protective film is not particularly limited, and for example, a method of forming by a sputtering can be appropriately employed. Further, the thickness of the protective film to be formed is not particularly limited as long as it can sufficiently exhibit the antioxidant function and the like. For example, when a protective film made of chromium is formed, the thickness is 2 What is necessary is just about 50 nm.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

(Synthesis Examples 1-4 and Comparative Synthesis Examples 1-3)
First, using an MgO single crystal substrate (trade name “MgO (100) single crystal substrate” manufactured by Furuuchi Chemical Co., Ltd.), an underlying material (an alloy of Cr and Ta (Synthesis Example 1), Ta ( Synthesis example 2), alloy with Cr / Mo (synthesis example 3), alloy with Fe / Mo (synthesis example 4), V (comparative synthesis example 1), alloy of Cr and V (comparative synthesis example 2), By thinly laminating Cr (Comparative Synthesis Example 3)) by sputtering, thin film forming substrates each having a base layer laminated thereon were obtained. In the sputtering, the degree of vacuum was set to 1.3 mTorr or less.

Next, an NdFeB thin film was formed on each thin film forming substrate obtained as described above by sputtering. As a sputtering method, a magnetron sputtering method was employed, and the ultimate vacuum before sputtering film formation was set to 1 × 10 ⁻⁸ Pa or less. The deposition rate was 0.4 Å / s, and the surface temperature of the substrate during sputtering was kept at 600 to 655 ° C. Furthermore, the target material was an NdFeB alloy, the shape of the formed thin film was a circle with a diameter of 8 mm, and the designed film thickness of the thin film was 5 nm.

In order to confirm the crystal phase of the NdFeB thin film thus formed, X-ray diffraction (XRD) measurement was performed on each thin film obtained. The XRD pattern of each thin film obtained in Synthesis Examples 1 to 4 and Comparative Synthesis Examples 1 to 3 is shown in FIG. As is clear from the results shown in FIG. 1, it was confirmed that when a material containing Mo or Ta was used as the base material, a c-plane oriented Nd ₂ Fe ₁₄ B phase grew. From these results, it is possible to grow a c-plane oriented Nd ₂ Fe ₁₄ B phase by using a thin film forming substrate in which a base layer made of a base material containing Mo or Ta is stacked on an MgO substrate. I found it possible.

(Examples 1-6 and Comparative Examples 1-6)
First, by using an MgO single crystal substrate (trade name “MgO (100) single crystal substrate” manufactured by Furuuchi Chemical Co., Ltd.), a base material made of Mo is flatly laminated on each substrate by sputtering. Each of the thin film forming substrates laminated with a film was obtained. In sputtering, the degree of vacuum was 1.3 mTorr or less, and the film thickness of the formed underlayer was 20 nm.

Next, an NdFeB thin film was formed on each thin film forming substrate obtained as described above by sputtering. As a sputtering method, a magnetron sputtering method was employed, and the ultimate vacuum before sputtering film formation was set to 1 × 10 ⁻⁸ Pa or less. The film formation rate was 0.4 Å / s, and the target materials were NdFeB alloys. The shape of the thin film formed was a circle having a diameter of 8 mm, and the designed film thickness of the thin film was 5 nm. Furthermore, the surface temperature of the substrate during sputtering was 600 ° C. (Example 1), 625 ° C. (Example 2), 635 ° C. (Example 3), and 645 ° C. for each Example and each Comparative Example. (Example 4), 655 ° C (Example 5), 665 ° C (Example 6), 500 ° C (Comparative Example 1), 520 ° C (Comparative Example 2), 540 ° C (Comparative Example 3), 560 ° C (Comparative) Example 4) The temperature was maintained at 580 ° C. (Comparative Example 5) and 675 ° C. (Comparative Example 6).

  Next, after the NdFeB thin film was laminated as described above, it was allowed to cool naturally until the temperature of the thin film reached room temperature (25 ° C.). Thereafter, a protective film made of chromium was laminated on the NdFeB thin film by sputtering. In the sputtering, the degree of vacuum was set to 1.3 mTorr or less. The thickness of the protective film was 10 nm.

<Evaluation of characteristics of NdFeB thin films obtained in Examples 1 to 6 and Comparative Examples 1 to 6>
<Observation by TEM>
The NdFeB thin film obtained in Example 1 was observed with a transmission electron microscope (TEM). A transmission electron microscope (TEM) photograph of the NdFeB thin film obtained in Example 1 is shown in FIG. From the results shown in FIG. 2, it was confirmed that the crystals of NdFeB were c-plane oriented.

<Observation by TEM-EELS>
Next, the state of iron in the cross sections of the NdFeB thin films obtained in Examples 1-2, Comparative Example 3, and Comparative Examples 5-6 was observed while selecting energy by TEM-EELS. As a result of such TEM-EELS measurement, a transmission electron microscope (TEM) photograph showing the state of iron in the cross section of the NdFeB thin film obtained in Examples 1-2, Comparative Example 3, and Comparative Examples 5-6 is shown. 3-7 (FIG. 3: Comparative Example 3, FIG. 4: Comparative Example 5, FIG. 5: Example 1, FIG. 6: Example 2, FIG. 7: Comparative Example 6)

  As is clear from the results shown in FIGS. 5 to 6, in the NdFeB thin films obtained in Examples 1 and 2, a discontinuous film is formed by isolated island particles (an island-like structure is formed). Confirmed). From the results shown in FIGS. 5 to 6, it was confirmed that the average values of the in-plane diameters of the island particles were 80 nm (Example 1) and 140 nm (Example 2). On the other hand, as apparent from the results shown in FIGS. 3 to 4, it was obtained when the surface temperature of the substrate was set to 540 ° C. or 580 ° C. during the sputtering (in the case of Comparative Example 3 and Comparative Example 5). The NdFeB thin film was confirmed to be a continuous film although the NdFeB layer had some irregularities. Furthermore, from the results shown in FIG. 7, it was confirmed that the NdFeB thin film obtained in Comparative Example 6 was a continuous film. Also, from the results shown in FIGS. 5 to 7, when the surface temperature of the substrate is 600 ° C. or higher during sputtering (Examples 1 and 2), island particles are formed, and the in-plane of the formed island particles It turned out that the average value of a diameter becomes the range of 40-140 nm. From such a result, in Examples 1-6, it turned out that the island-like thin film by which the island particle whose average value of an in-plane diameter is 40-140 nm is arrange | positioned at discontinuous film form is obtained.

<XRD measurement>
XRD measurement was performed on the NdFeB thin films obtained in Examples 1 to 6 and Comparative Examples 1 to 6 in order to confirm the presence or absence of Nd ₂ Fe ₁₄ B phase generation. The graph which shows the XRD pattern of the NdFeB thin film obtained in Examples 1-6 and Comparative Examples 1-6 is shown in FIG.

As is apparent from the results shown in FIG. 8, when the surface temperature of the substrate during sputtering is 540 to 665 ° C. (in the case of Examples 1 to 6 and Comparative Examples 1 to 5), It was confirmed that an Nd ₂ Fe ₁₄ B phase with c-plane orientation was grown on the surface. On the other hand, when the surface temperature of the substrate during sputtering was 675 ° C., it was confirmed that the substrate was transformed into a phase other than the Nd ₂ Fe ₁₄ B phase.

<Measurement of magnetic properties>
The coercive force of each NdFeB thin film obtained in Examples 1 to 6 and Comparative Examples 1 to 6 was measured with a sample vibration type magnetometer (VSM: manufactured by Lake Shore). A graph showing the relationship between the coercivity of each NdFeB thin film obtained in Examples 1 to 6 and Comparative Examples 1 to 6 and the retention temperature of the substrate surface during film formation is shown in FIG.

As is apparent from the results shown in FIG. 9, when the substrate surface holding temperature during film formation was 600 ° C. to 665 ° C. (Examples 1 to 6), the coercive force of the obtained NdFeB thin film was 15 KOe. It has been confirmed that On the other hand, when the holding temperature of the substrate surface during film formation was 675 ° C. (Comparative Example 6), the coercive force of the obtained NdFeB thin film was approximately 10 Oe or less. From these results, it was confirmed that the NdFeB thin films obtained in Examples 1 to 6 exhibited a sufficiently high coercive force. Moreover, since the coercive force of the NdFeB thin film obtained in Comparative Example 6 was 10 Oe or less, it was found that Nd ₂ Fe ₁₄ B was not formed in the NdFeB thin film obtained in Comparative Example 6.

<Observation by AFM>
The NdFeB thin films obtained in Examples 1-2, Example 4, Comparative Example 3, Comparative Example 5, and Comparative Example 6 were observed with an atomic force microscope (AFM). Atomic force microscope (AFM) photographs of the respective NdFeB thin films obtained by such observation are shown in FIGS. 10 is an AFM photograph of the NdFeB thin film obtained in Comparative Example 3, FIG. 11 is an AFM photograph of the NdFeB thin film obtained in Comparative Example 5, and FIG. 12 is obtained in Example 1. FIG. 13 is an AFM photograph of the NdFeB thin film obtained in Example 2, FIG. 14 is an AFM photograph of the NdFeB thin film obtained in Example 4, and FIG. 4 is an AFM photograph of the NdFeB thin film obtained in Comparative Example 6.

  As is clear from the results shown in FIGS. 12 to 14, it was confirmed that the film structures of the NdFeB thin films obtained in Examples 1 and 2 and Example 4 were island-shaped structures. Further, according to such AFM photographs, in each of the NdFeB thin films obtained in Examples 1 and 2 and Example 4, the average value of the separation distance between adjacent particles at the formed island particles was 28 nm ( Example 1), 32 nm (Example 2), and 75 nm (Example 4) were confirmed.

  From the result of the characteristic evaluation as described above, an MgO single crystal substrate was used to form a base layer made of a base material containing at least one of Mo and Ta, and the surface temperature of the thin film forming substrate was 600 ° C. ( Example 1), 625 ° C. (Example 2), 635 ° C. (Example 3), 645 ° C. (Example 4), 655 ° C. (Example 5) or 665 ° C. (Example 6) while maintaining NdFeB It was found that by forming a thin film by sputtering, an island-like magnetic thin film having a sufficiently thin thickness and in which isolated island particles made of a magnetic material are arranged in a discontinuous film shape can be obtained. Moreover, in the thin film obtained in Examples 1-6, it turned out that the average value of the in-plane particle diameter of an island particle becomes the range of 40-140 nm. Furthermore, it was found that the island-shaped magnetic thin films obtained in Examples 1 to 6 have a sufficiently high coercive force.

  As described above, according to the present invention, a magnetic thin film made of a magnetic material containing a rare earth element is formed, and an island-like structure in which isolated island particles made of the magnetic material are arranged in a discontinuous film shape is formed. In addition, it is possible to provide an island-shaped magnetic thin film capable of having a sufficiently small coercive force and a manufacturing method thereof, in which the island particles have a sufficiently small particle size, a sufficiently thin film thickness, and a sufficiently high coercive force. . Therefore, the island-shaped magnetic thin film of the present invention is particularly useful as a magnetic thin film used for an ultra-high density magnetic medium capable of processing and recording information.

It is a graph which shows the XRD pattern of each thin film obtained by the synthesis examples 1-4 and the comparative synthesis examples 1-3. 2 is a transmission electron microscope (TEM) photograph of the NdFeB thin film obtained in Example 1. FIG. It is a transmission electron microscope (TEM) photograph which shows the state of the iron of the cross section of the NdFeB thin film obtained in the comparative example 3. 10 is a transmission electron microscope (TEM) photograph showing the state of iron in the cross section of the NdFeB thin film obtained in Comparative Example 5. 2 is a transmission electron microscope (TEM) photograph showing the state of iron in the cross section of the NdFeB thin film obtained in Example 1. FIG. 4 is a transmission electron microscope (TEM) photograph showing the state of iron in the cross section of the NdFeB thin film obtained in Example 2. FIG. 6 is a transmission electron microscope (TEM) photograph showing the state of iron in the cross section of the NdFeB thin film obtained in Comparative Example 6. It is a graph which shows the XRD pattern of each NdFeB thin film obtained in Examples 1-6 and Comparative Examples 1-6. It is a graph which shows the relationship between the coercive force of each NdFeB thin film obtained in Examples 1-6 and Comparative Examples 1-6, and the retention temperature of the substrate surface at the time of film-forming of each thin film. 4 is an atomic force microscope (AFM) photograph of the NdFeB thin film obtained in Comparative Example 3. 6 is an atomic force microscope (AFM) photograph of the NdFeB thin film obtained in Comparative Example 5. 2 is an atomic force microscope (AFM) photograph of the NdFeB thin film obtained in Example 1. 4 is an atomic force microscope (AFM) photograph of the NdFeB thin film obtained in Example 2. 4 is an atomic force microscope (AFM) photograph of the NdFeB thin film obtained in Example 4. 6 is an atomic force microscope (AFM) photograph of the NdFeB thin film obtained in Comparative Example 6.

Claims (7)

  An island-like magnetic thin film in which isolated island particles made of a magnetic material are arranged in a discontinuous film shape, wherein the magnetic material contains a rare earth element, and an average value of in-plane diameters of the island particles is 40 An island-shaped magnetic thin film characterized by being in a range of ˜140 nm and a thickness of the thin film in a range of 2-25 nm.   The island-shaped magnetic thin film according to claim 1, wherein the magnetic material contains neodymium.   The island-shaped magnetic thin film according to claim 1 or 2, wherein the magnetic material contains neodymium, iron, and boron.   4. The island-shaped magnetic thin film according to claim 1, wherein an average value of distances between closest points of the closest particles of the island particles is in a range of 10 to 100 nm.   5. The island-shaped magnetic thin film according to claim 1, wherein a crystal phase of the magnetic material in the island particles is c-plane oriented. Forming a base layer made of a base material containing at least one of molybdenum and tantalum on a substrate made of a magnesium oxide single crystal to obtain a magnetic thin film forming substrate;
By sputtering a target material containing neodymium, iron and boron while maintaining the surface temperature of the magnetic thin film forming substrate at 590 ° C. to 670 ° C.,
Isolated island particles made of a magnetic material containing neodymium, iron and boron are arranged in a discontinuous film shape, and the crystal phase of the magnetic material in the island particles is c-plane oriented, and the island particles Forming an island-shaped magnetic thin film having an average in-plane diameter of 40 to 140 nm and a thickness of 2 to 25 nm on the underlayer;
A method for producing an island-shaped magnetic thin film comprising:   The method for producing an island-shaped magnetic thin film according to claim 6, wherein a film forming rate of the magnetic thin film by sputtering is 1 Å / s or less.