JP2013105506A - Microwave assisted magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microwave assisted magnetic recording medium in which writing can be performed by a high frequency magnetic field of lower frequency than a ferromagnetic resonance frequency of a recording layer.SOLUTION: A microwave assisted magnetic recording medium 10 comprises: a substrate 1; a base layer 2 formed on the substrate 1; a soft magnetic layer 4, a recording layer 3 and a protective layer 5 formed on the base layer 2. A reversal magnetic field of the recording layer 3 is controlled by a spin wave induced in the soft magnetic layer 4. Since the soft magnetic layer 4 has a spin wave frequency lower than the ferromagnetic resonance frequency of the recording layer 3, writing can be performed by the high frequency magnetic field having lower frequency. When the recording layer 3 has a magnetic anisotropy of 5×10J/mor greater and a thickness of 20 nm or less, and the soft magnetic layer 4 has a magnetic anisotropy of 5×10J/mor less and a thickness of 20 nm to 150 nm, the spin wave is propagated into the recording layer by a high frequency magnetic field of 1 GHz to 15 GHz, thereby significantly reducing a magnetic coercive force of the recording layer.

Description

  The present invention relates to a microwave assisted magnetic recording medium. More specifically, the present invention relates to a magnetic recording medium that can be written by applying a microwave.

  A magnetic recording medium used in a hard disk storage device records information “1” and “0” in the direction of the magnetic material. In order to increase the density of this magnetic recording medium, it is necessary to reduce the volume of the magnetic material used for the recording layer. The magnetic material used for the recording layer is required to have thermal stability of magnetization against disturbance due to external thermal energy in order to record information stably.

The following equation (1) is generally established for the thermal stability Δ of magnetization and the magnetic anisotropy energy K.
Here, V is the volume of the magnetic material, k _B is the Boltzmann constant, and T is the temperature.

  As can be seen from the equation (1), in the case where the volume of the magnetic material is decreased as the magnetic recording density is increased, in order to ensure the thermal stability of magnetization, the recording layer has a material having high magnetic anisotropy energy. Is required.

On the other hand, as the magnetic anisotropy energy of the recording layer increases, there also arises a problem that the magnetic field required for writing information from the outside increases. Assuming a simultaneous magnetization reversal mode in which the magnetization is uniformly reversed, the following equation (2) is established between the magnetic anisotropy energy, the coercive force H _c, and the anisotropic magnetic field H _k .
Here, M _s is the value of the saturation magnetization of the magnetic material.

For example, it is assumed that the magnetic recording layer is made of grains having a diameter of 5 nm with M _s of 1000 emu / cm ³ (1.26 Wb / m ² ). In general, Δ is required to be 60 or more, and magnetic anisotropy energy of about 4 × 10 ⁷ erg / cm ³ (4 × 10 ⁶ J / m ³ ) is required at room temperature.

On the other hand, H _c is 80kOe (Oe is Oersted, 6.4 mA / m) of the particles is, must be applied a magnetic field of more than H _c is to reverse the magnetization of the recording layer. In the current magnetic recording system, the magnetization of the recording layer is reversed by the magnetic field from the write magnetic head, but a magnetic field of about 10 kOe (0.8 MA / m) is the limit of the magnetic field that can be applied from the write magnetic head.

  In order to solve this problem, for example, as disclosed in Patent Document 1, by applying a high-frequency magnetic field in the GHz band simultaneously to the external magnetic field to the recording layer, the magnetization precession of the magnetic material in the recording layer is excited. However, microwave-assisted magnetization reversal that performs dynamic magnetization reversal has been studied.

  In order to reverse the magnetization of the magnetic material of the recording layer in the opposite direction from the initial state, it is necessary to add energy for overcoming the energy barrier determined by the magnetic anisotropy energy. Since a material having high magnetic anisotropy has a high energy barrier, it is necessary to overcome the energy barrier by applying a large external magnetic field corresponding to the energy barrier.

The principle of microwave-assisted magnetization reversal refers to a method of inducing magnetization reversal with a low external magnetic field by applying a high-frequency magnetic field of the same level as the resonance frequency of the recording layer, as shown in Patent Document 1. The magnetization of the magnetic substance precesses around the effective magnetic field H _{eff at} a finite temperature. The frequency f _FMR at that time is given by the following equation (3). This f _FMR is called a ferromagnetic resonance frequency.
Here, γ is a gyromagnetic factor.

When a high-frequency magnetic field having the same frequency is applied to the magnetization precessed by f _FMR in the recording layer, the high-frequency magnetic field and the precession of magnetization resonate, and the amplitude of the precession is amplified. Magnetization with amplified precession can overcome the energy barrier due to the amplified precession even under an external magnetic field lower than the energy barrier, and finally magnetization reversal occurs. This is microwave assisted magnetization reversal.

  Non-Patent Document 1 investigates the coercivity of a cobalt fine particle used in the recording layer when a high frequency magnetic field is applied, and reports that the coercivity of the cobalt fine particle is reduced by applying a high frequency magnetic field close to the ferromagnetic resonance frequency. ing.

  In Non-Patent Document 2, it is assumed that an oscillator that generates a high-frequency magnetic field by rotating the magnetization of a magnetic material with an electric current is mounted on a magnetic head for a magnetic recording medium, and the generated high-frequency magnetic field is applied to the magnetic recording medium. The effect on writing is examined by computer simulation. As a result, it has been reported that the coercive force is greatly reduced in the vicinity of the ferromagnetic resonance frequency of the recording layer.

  Further, in Non-Patent Document 3, it is shown that a reduction in coercive force due to a high-frequency magnetic field can be effectively achieved by combining a soft magnetic layer having a low magnetic anisotropy and a hard magnetic layer having a high magnetic anisotropy as a recording layer. Reported from simulation.

JP 2010-257539 A

CHRISTOPHE THIRION et al., “Switching of magnetization by nonlinear resonance studied in single nanoparticles”, Nature Materials, vol.2, p.524, 2003 Jian-Gang Zhu et al., “Microwave Assisted Magnetic Recording”, IEEE Trans. Magn., Vol.44, p.125, 2008 T. J. Fal et al., “Domain wall and microwave assisted switching in an exchange spring bilayer”, J. Appl. Phys., Vol.109, p.093911, 2011

  To date, the advantages of microwave-assisted magnetization reversal have been reported from experiments and calculations, but when high-density magnetic recording is taken into consideration, the frequency of the high-frequency magnetic field applied as the magnetic anisotropy of the recording layer increases There is a new issue of becoming higher.

For example (3) in the effective field of the equation, since the anisotropy field is also included, if the H _k is 80kOe, f _FMR exceeds 200 GHz. It is technically difficult to mount such a sub-THZ small oscillator on a write magnetic head.

  Furthermore, at present, when the recording layer having a large coercive force is irradiated with microwaves, the reduction rate is at most about 60% to 70%, and the reduction rate is not sufficient from the viewpoint of mounting.

  In view of the above problems, an object of the present invention is to provide a microwave assisted magnetic recording medium capable of writing with a high-frequency magnetic field having a frequency lower than the ferromagnetic resonance frequency of a recording layer.

  In order to achieve the above object, a microwave assisted magnetic recording medium of the present invention comprises a substrate, an underlayer formed on the substrate, a soft magnetic layer formed on the underlayer, a recording layer, and a protective layer. In addition, the reversal magnetic field of the recording layer is controlled by a spin wave induced in the soft magnetic layer by applying a high frequency.

In the above configuration, the recording layer and the soft magnetic layer are preferably exchange-coupled magnetically at the interface.
The frequency of the spin wave in the soft magnetic layer is preferably lower than the ferromagnetic resonance frequency of the recording layer.
The recording layer preferably has a magnetic anisotropy of 5 × 10 ⁵ J / m ³ or more. The thickness of the recording layer is preferably 20 nm or less.
The soft magnetic layer preferably has a magnetic anisotropy of 5 × 10 ⁵ J / m ³ or less. The thickness of the soft magnetic layer is preferably in the range of 20 nm to 150 nm.
The magnetization direction of the recording layer is perpendicular to the in-plane direction of the substrate.

  According to the microwave assisted magnetic recording medium of the present invention, the reversal magnetic field of the recording layer can be controlled by the spin wave induced in the soft magnetic layer, and in a GHz band significantly lower than the ferromagnetic resonance frequency of the recording layer. The reversal magnetic field of the recording layer can be reduced, and the recording density of the recording layer can be improved. For example, the soft magnetic layer and the recording layer are magnetically exchange-coupled at the interface, and the thickness of the soft magnetic layer is increased in the range of 20 nm to 150 nm, thereby being induced in the soft magnetic layer by a high frequency magnetic field of 1 GHz to 15 GHz. Thus, the collective motion of magnetization that is spatially non-uniform, that is, the spin wave can be propagated into the recording layer to reduce the coercivity of the recording layer.

It is sectional drawing which shows the structure of the microwave assisted magnetic recording medium based on this invention. It is a figure which shows typically the mechanism which writes in the microwave assisted magnetic recording medium of this invention. It is a magnetization curve which the magnetic multilayer film which comprises the microwave assisted magnetic recording medium based on this invention shows. 4 is a magnetization curve of a low magnetic field in FIG. It is a figure which shows the anisotropic magnetoresistive effect when not applying a high frequency magnetic field with respect to the magnetic multilayer film which comprises a microwave assisted magnetic recording medium. It is a figure which shows the anisotropic magnetoresistive effect at the time of applying a high frequency magnetic field with respect to the magnetic multilayer film which comprises a microwave assisted magnetic recording medium. It is a figure which shows the frequency dependence of the reversal magnetic field at the time of applying a high frequency magnetic field with respect to the magnetic multilayer film which comprises a microwave assisted magnetic recording medium. It is a figure which shows the measurement result of the ferromagnetic resonance frequency in the magnetic multilayer film which comprises a microwave assisted magnetic recording medium.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a sectional view showing the structure of a microwave assisted magnetic recording medium 10 according to the present invention.
In the embodiment shown in FIG. 1, the microwave assisted magnetic recording medium 10 is formed on the base layer 2 formed on the substrate 1, the recording layer 3 formed on the base layer 2, and the recording layer 3. The soft magnetic layer 4 and the protective layer 5 formed on the soft magnetic layer 4 are stacked in this order.
As the substrate 1, a single crystal substrate can be used. As the substrate 1, an MgO substrate, a Si substrate, a glass substrate, or the like can be used. By providing an appropriate underlayer 2 such as an MgO layer on the substrate 1, a magnetic multilayer film of the microwave assisted magnetic recording medium 10 can be produced.

  The underlayer 2 is a layer inserted in order to improve the crystal quality and orientation of the recording layer 3 and the like when a magnetic multilayer film such as the recording layer 3 is formed on the substrate 1. The underlayer 2 is also called a buffer layer. As the underlayer 2, for example, a layer made of Fe (iron) or Au (gold) can be used. As shown in FIG. 1, the base layer 2 may be configured by a first base layer 2a and a second base layer 2b.

The recording layer 3 is a layer for recording magnetism in the horizontal direction or the vertical direction with respect to the magnetic multilayer film surface of the microwave assisted magnetic recording medium 10. The recording layer 3 is a layer that is magnetically coupled to the soft magnetic layer 4. In order to increase the recording density of the microwave assisted magnetic recording medium 10, it is desirable to perform perpendicular recording on the magnetic multilayer film surface of the microwave assisted magnetic recording medium 10, that is, perpendicular magnetic recording. In this case, the recording direction of the recording layer 3 is the Y direction, which is the vertical direction of the paper surface of FIG. 1, and the magnetization direction of the recording layer 3 is perpendicular to the in-plane direction of the substrate 1. As the material of the recording layer 3, a ferromagnetic material having high magnetic anisotropy is used. Such ferromagnetic, L1 ₀ type iron platinum ordered alloy, Co-Pt alloy, Fe-Pd alloy, Co-Pd alloys.

Unlike the recording layer 3, the soft magnetic layer 4 is made of a material having no hysteresis in the magnetization characteristics. The soft magnetic layer 4 is also called a soft magnetic backing layer. The soft magnetic layer 4 is made of, for example, a permalloy alloy Fe ₁₉ Ni ₈₁ .

  As the soft magnetic layer 4, a soft magnetic material such as a Co-Fe alloy can be used, but it is desirable to use a permalloy alloy layer having a low magnetic anisotropy.

FIG. 2 is a diagram schematically showing a mechanism for writing to the microwave assisted magnetic recording medium 20 of the present invention. As shown in FIG. 2, a write magnetic head 30 is disposed on the microwave assisted magnetic recording medium 20.
The microwave assisted magnetic recording medium 20 includes an underlayer 2 formed on the substrate 1, a soft magnetic layer 4 formed on the underlayer 2, a recording layer 3 formed on the soft magnetic layer 4, and a recording The protective layer 5 formed on the layer 3 has a structure laminated in this order. The microwave assisted magnetic recording medium 10 of the embodiment shown in FIG. 1 has the same configuration except that the stacking of the soft magnetic layer 4 and the recording layer 3 is reversed.

  A DC magnetic field for writing is applied to the opening 30 a of the write magnetic head 30 and a high frequency magnetic field is applied in a superimposed manner. In order to improve the recording density of the microwave assisted magnetic recording medium 10, the size of the opening 30a is preferably as small as possible. However, since it is difficult to generate a steep DC magnetic field if the size of the opening 30a is too small, the size of the opening 30a is, for example, about 100 nm in order to generate a steep DC magnetic field.

  A spin torque oscillator may be disposed in the opening 30a of the write magnetic head 30 in order to apply a high-frequency magnetic field. A spin torque oscillator is composed of a giant magnetoresistive element or a tunnel magnetoresistive element, and oscillates a microwave when a direct current is applied. Since the spin torque oscillator is on the order of nm, it is a small oscillator that can be accommodated even if the size of the writing region is reduced.

According to the microwave assisted magnetic recording medium 10 of the present invention, the recording layer 3 is generated by a spin wave induced by applying a high-frequency magnetic field in the soft magnetic layer 4 that is magnetically exchange-coupled to the interface of the recording layer 3. Thus, the magnetization of the recording layer 3 can be easily reversed by the high frequency magnetic field applied to the microwave assisted magnetic recording medium 10. This phenomenon of magnetization reversal occurs by following the following process.
First, the magnetization in the soft magnetic layer 4 causes non-uniform motion due to the spin wave induced in the soft magnetic layer 4. Next, the magnetization of the recording layer 3 that is in magnetic exchange coupling with the soft magnetic layer 4 is also affected by the soft magnetic layer 4, and the movement of magnetization in the recording layer 3 is induced. Due to the motion induced by the magnetization in the recording layer 3, magnetization reversal of the recording layer 3 occurs.
As a result, the DC magnetic field for reversing the magnetization direction of the recording layer 3 can be reduced, and the DC magnetic field required for writing to the microwave assisted magnetic recording medium 10 performing perpendicular magnetic recording can be reduced. Furthermore, by applying a high frequency magnetic field from the narrow opening 30 a of the write magnetic head 30, the recording density of the microwave assisted magnetic recording medium 10 can be improved.

The frequency of the spin wave induced by applying a high-frequency magnetic field in the soft magnetic layer 4 is in the GHz band that is one digit or more lower than the ferromagnetic resonance frequency of the recording layer 3, for example, a sub THz of 200 GHz when H _k is 80 kOe. Become. An oscillator that applies a high-frequency magnetic field in the GHz band is easier to realize than a sub-THZ oscillator, and thus the writing magnetic head 30 can be manufactured more easily.

  In order to set the frequency of the spin wave induced by applying a high-frequency magnetic field in the soft magnetic layer 4 to a GHz band that is lower than the ferromagnetic resonance frequency of the recording layer 3, for example, 1 to 10 GHz. The configuration of the wave-assisted magnetic recording medium 10, particularly the thickness and magnetic anisotropy of the recording layer 3 and the soft magnetic layer 4, can be designed as parameters. The frequency at which the spin wave mode is excited can be obtained by analytical calculation or simulation.

In the microwave assisted magnetic recording medium 10 in which the recording layer 3 is made of Fe ₄₈ Pt ₅₂ and the soft magnetic layer 4 is made of Fe ₁₉ Ni ₈₁ , the spin wave mode is set in the soft magnetic layer 4 under the following conditions. The excited frequency can be set to a frequency lower than about 15 GHz or less, which is the ferromagnetic resonance frequency of the recording layer 3.
(1) The soft magnetic layer 4 has a magnetic anisotropy of 5 × 10 ⁶ erg / cm ³ (5 × 10 ⁵ J / m ³ ) or less, and the thickness of the soft magnetic layer 4 is in the range of 20 nm to 150 nm. To do.
(2) The recording layer 3 has a magnetic anisotropy of 5 × 10 ⁶ erg / cm ³ (5 × 10 ⁵ J / m ³ ) or more, and the thickness of the recording layer 3 is 20 nm or less.
The characteristics of the microwave assisted magnetic recording medium 10 of the present invention described above can be applied to both perpendicular magnetic recording and horizontal magnetic recording regardless of the recording direction of the recording layer 3.
Hereinafter, the present invention will be described in more detail with reference to examples.

The microwave assisted magnetic recording medium 10 shown in FIG. 1 was produced as follows.
The Fe ₄₈ L1 ₀ type iron platinum ordered alloy having a composition consisting of Pt ₅₂ as the recording layer 3, also microwave assisted magnetic recording medium has a permalloy alloy having a composition consisting of Fe ₁₉ Ni ₈₁ as a soft magnetic layer 4 10 Was made. Hereinafter, the recording layer 3 is called an iron-platinum ordered alloy layer, and the soft magnetic layer 4 is called a permalloy alloy layer.

  The magnetic multilayer film of the microwave assisted magnetic recording medium 10 was deposited on the substrate 1 made of MgO having a thickness of 500 μm by using a sputtering method. A base layer 2a made of Fe having a thickness of 1 nm and a base layer 2b made of Au having a thickness of 40 nm are formed at room temperature, and the iron-platinum ordered alloy layer 3 having a thickness of 10 nm is formed at a substrate temperature of 450 ° C. Filmed. Thereafter, a permalloy alloy layer 4 having a thickness of 100 nm was formed at room temperature. Finally, a protective layer 5 made of Au having a thickness of 3 nm was formed at room temperature.

FIG. 3 is a magnetization curve shown by the magnetic multilayer film constituting the microwave assisted magnetic recording medium 10 according to the present invention, and FIG. 4 is a low magnetic field magnetization curve of FIG. 3 and 4, the horizontal axis represents the applied magnetic field H (kOe), and the vertical axis represents the magnetization M (emu / cm ³ ). A magnetic field applied to the microwave assisted magnetic recording medium 10 was applied in the direction of the easy magnetization axis in the film plane.
As shown in FIGS. 3 and 4, the magnetization curve shows a two-stage loop behavior, and the first stage seen in the vicinity of the low magnetic field is due to the start of the magnetization reversal of the permalloy alloy layer 4 (FIG. 4). The second stage of the high magnetic field corresponds to the magnetization reversal of the iron-platinum ordered alloy layer 3 (see the dotted line data in FIG. 4).

  In the microwave assisted magnetic recording medium 10, when the magnetic field is returned to zero after the magnetization reversal of the permalloy alloy layer 4 is started and before the magnetization reversal of the iron-platinum ordered alloy layer 3 occurs, the reversible magnetization behavior (spring (Referred to as solid line data in FIG. 4). This is because the permalloy alloy layer 4 and the iron-platinum ordered alloy layer 3 are exchange-coupled at the interface and are pinned by the iron-platinum ordered alloy layer 3 even when the magnetization of the permalloy alloy layer 4 starts to reverse. This means that the magnetization is not completely reversed, and the magnetic field is reversibly restored to the original state.

  From the above results, it can be seen that the magnetization in the permalloy alloy layer 4 is spatially twisted. Also in the magnetic multilayer film of the microwave assisted magnetic recording medium 10 in which the film thickness of the permalloy alloy layer 4 was changed in the range of 20 nm to 150 nm, reversible magnetization behavior was observed as in FIGS.

  Next, the produced magnetic multilayer film 10 was processed into a rectangular shape having a minor axis of 2 μm and a major axis of 50 μm by a microfabrication method, the protective layer 5, the permalloy alloy layer 4, and the iron platinum ordered alloy layer 3. Further, the base layer 2a made of Fe and the base layer 2b made of Au were processed into a coplanar waveguide shape, and a structure capable of applying a high frequency magnetic field to the microwave assisted magnetic recording medium 10 was manufactured.

FIG. 5 is a diagram showing the anisotropic magnetoresistance effect when a high frequency magnetic field is not applied to the magnetic multilayer film constituting the microwave assisted magnetic recording medium 10. The anisotropic magnetoresistive effect is called AMR (Anisotropic Magneto-Resistance). The horizontal axis in FIG. 5 is the applied magnetic field H (Oe), and the vertical axis is the resistance change from the element resistance in the magnetization saturation state, that is, ΔR (Ω). The film thickness of the permalloy alloy layer 4 is 120 nm.
AMR is an effect that the electric resistance changes depending on the relative angle between the current and the magnetization. The resistance is high when the current and the magnetization are parallel, and the resistance decreases when the current and the magnetization are perpendicular.
As shown in FIG. 5, in the rectangular element manufactured by processing the microwave assisted magnetic recording medium 10, the relative angle between the magnetization and the current is increased by twisting the magnetization in the permalloy layer when a magnetic field is applied. Therefore, the resistance decreases. When the iron-platinum ordered alloy layer 3 serving as the recording layer 3 is reversed in magnetization by increasing the magnetic field, the resistance value returns to the original value. As described above, in a state where no high frequency magnetic field is applied to the microwave assisted magnetic recording medium 10, the iron-platinum ordered alloy layer 3 is reversed in magnetization by a magnetic field of 2 kOe (see arrow (↑) in FIG. 5).

FIG. 6 is a diagram showing an anisotropic magnetoresistance effect when a high frequency magnetic field is applied to the magnetic multilayer film constituting the microwave assisted magnetic recording medium 10. The vertical and horizontal axes in FIG. 6 are the same as those in FIG. The frequency of the applied high frequency magnetic field is 7 GHz, and the high frequency magnetic field (H _rf ) is 143 Oe.
As is clear from FIG. 6, by applying a high frequency magnetic field (H _rf ) 143 Oe of 7 GHz, the magnetization of the iron-platinum ordered alloy layer 3 was reversed by a magnetic field of 250 Oe (see arrow (↑) in FIG. 6).

The reduction rate with respect to the reversal magnetic field (corresponding to the coercive force) when the high-frequency magnetic field shown in FIG.
Here, H _c (H _rf ) is a reversal magnetic field when a high frequency magnetic field is applied.
From the above equation (4), in the microwave assisted magnetic recording medium 10, by applying a high frequency magnetic field, a reduction rate of the reversal magnetic field of 81% at maximum was obtained compared to the case where no high frequency magnetic field was applied.

FIG. 7 is a diagram showing the frequency dependence of the reversal magnetic field when a high frequency magnetic field is applied to the magnetic multilayer film constituting the microwave assisted magnetic recording medium 10. The horizontal axis in FIG. 7 is the frequency (GHz) of the high-frequency magnetic field, and the vertical axis is the reversal magnetic field H _SW (Oe). The film thickness of the permalloy alloy layer 4 is 120 nm, and the strength of the applied high frequency magnetic field is 143 Oe.
As is apparent from FIG. 7, no change in the reversal magnetic field is observed in the low frequency region, and the reversal magnetic field rapidly decreases in the vicinity of 7 GHz. As the frequency is further increased, the reversal magnetic field gradually increases. The frequency of the high-frequency magnetic field at which the reversal field decreases is near 7 GHz, which is found to be lower than the ferromagnetic resonance frequency (15 GHz or higher) expected from the magnetic anisotropy energy of the iron-platinum ordered alloy layer 3. did.

FIG. 8 shows the measurement result of the ferromagnetic resonance frequency in the magnetic multilayer film constituting the microwave assisted magnetic recording medium 10. The horizontal axis in FIG. 8 is the frequency (GHz) of the high-frequency magnetic field, and the vertical axis is the change in the real part of S parameter S11, Re (ΔS11). The film thickness of the permalloy alloy layer 4 is 120 nm, and the intensity of the applied DC magnetic field is −500 Oe. This DC magnetic field is applied in the direction opposite to the magnetization direction of the iron-platinum ordered alloy layer 3 in the in-plane direction of the magnetic multilayer film, and the magnetization of the permalloy alloy layer 4 is spatially twisted. Applicable to the area.
As is clear from FIG. 8, it can be seen that peaks of the ferromagnetic resonance frequency are observed in the vicinity of 7 GHz, in the vicinity of 8 GHz, and in the vicinity of 11 GHz (see the arrow (↓) in FIG. 7). These frequencies are attributed to the low-order spin wave modes in the permalloy alloy layer 4 in order from the lowest frequency peak. From these results, it can be seen that the frequency of 7 GHz at which the reversal magnetic field rapidly decreased corresponds to the spin wave mode in the permalloy alloy layer 4, and the reversal magnetic field of the iron-platinum ordered alloy layer 3 can be reduced using this mode.

  In the above embodiment, the measurement result that the reversal magnetic field of the recording layer 3 can be reduced when recording in the horizontal direction within the plane of the magnetic multilayer film constituting the microwave assisted magnetic recording medium 10 has been described. Of course, similar measurement results can be obtained when magnetic recording is performed in the perpendicular direction of the microwave-assisted magnetic recording medium 10.

  The present invention is not limited to the above embodiment, and various modifications are possible within the scope of the invention described in the claims, and it goes without saying that these are also included in the scope of the present invention. Nor.

1: Substrate 2: Underlayer 2a: First underlayer 2b: Second underlayer 3: Recording layer 4: Soft magnetic layer 5: Protection layer 10, 20: Microwave-assisted magnetic recording medium 30: Write magnetic head 30a :Aperture

Claims (8)

A substrate, a base layer formed on the substrate, a soft magnetic layer formed on the base layer, a recording layer, and a protective layer,
A microwave-assisted magnetic recording medium, wherein a reversal magnetic field of the recording layer is controlled by a spin wave induced in the soft magnetic layer by applying a high frequency.   The microwave assisted magnetic recording medium according to claim 1, wherein the recording layer and the soft magnetic layer are magnetically exchange-coupled at an interface.   The microwave assisted magnetic recording medium according to claim 1, wherein a frequency of a spin wave of the soft magnetic layer is lower than a ferromagnetic resonance frequency of the recording layer. The microwave assisted magnetic recording medium according to claim 1, wherein the recording layer has a magnetic anisotropy of 5 × 10 ⁵ J / m ³ or more.   The microwave assisted magnetic recording medium according to claim 1 or 2, wherein the recording layer has a thickness of 20 nm or less. The microwave assisted magnetic recording medium according to claim 1, wherein the soft magnetic layer has a magnetic anisotropy of 5 × 10 ⁵ J / m ³ or less.   The microwave assisted magnetic recording medium according to claim 1, wherein the soft magnetic layer has a thickness in a range of 20 nm to 150 nm.   The microwave assisted magnetic recording medium according to claim 1, wherein the magnetization direction of the recording layer is perpendicular to the in-plane direction of the substrate.