JP2007242099A - Magnetic recording medium for perpendicular magnetic recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium for perpendicular magnetic recording capable of effectively suppressing a WATER (Wide Area Track ERasure) phenomenon by providing desired coercive force. <P>SOLUTION: In the magnetic recording medium A for perpendicular magnetic recording provided with a plurality of soft magnetic films 2 and 4 as a backing layer 10 to a magnetic recording layer 6, a non-magnetic layer 3 is provided between the plurality of soft magnetic films 2 and 4 so as to cause coercive force of desired intensity. The plurality of soft magnetic films 2 and 4 have the same composition and the same thickness, wherein magnetization directions with an external magnetic field in an inactive state are formed so as to be reverse to each other in a layered plane. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium for perpendicular magnetic recording.

  A conventional magnetic recording medium for perpendicular magnetic recording is described in Patent Document 1. The magnetic recording medium described in this document includes a magnetic recording layer (perpendicular magnetic recording film) that maintains the magnetization direction in the vertical direction, two soft magnetic layers (soft magnetic films) provided as the backing layer, and a soft recording layer. An antiferromagnetic film provided between the magnetic layers is provided. According to such a configuration, effects such as reduction of noise from the backing layer and spike noise are expected.

JP 2005-285149 A

  However, in a configuration in which an antiferromagnetic film is provided between two soft magnetic layers as in the conventional magnetic recording medium, the so-called WATER (Wide Area Track ERasure) phenomenon in which recorded information disappears over a wide area of the magnetic recording layer. It was not so effective in suppressing the coercive force, and a coercive force with an appropriate strength could not be obtained.

  The present invention has been conceived under the circumstances described above, and provides a magnetic recording medium for perpendicular magnetic recording capable of effectively suppressing the WATER phenomenon with a desired coercive force. Is the issue.

  In order to solve the above problems, the present invention takes the following technical means.

  A magnetic recording medium for perpendicular magnetic recording provided by the present invention is a magnetic recording medium for perpendicular magnetic recording comprising a plurality of soft magnetic layers as a backing layer for the magnetic recording layer. In the meantime, a nonmagnetic layer is provided so as to generate a coercive force having a desired strength.

  Preferably, the plurality of soft magnetic layers have the same composition and the same thickness, and are formed such that magnetization directions in a state where an external magnetic field does not act are opposite to each other in the layer plane.

  Preferably, the thickness of the nonmagnetic layer is such that the strength of the coercive force is Hc, the strength of the exchange magnetic field generated between the plurality of soft magnetic layers is Hs, and the strength of the anisotropic magnetic field of the soft magnetic layer is Hk. Is set so that the following equation holds.

  According to such a configuration, since the nonmagnetic layer is provided between the plurality of soft magnetic layers, an exchange magnetic field (Hs) due to antiferromagnetic coupling can be generated with an appropriate strength between the soft magnetic layers. Thus, the WATER phenomenon can be effectively suppressed by giving a desired coercive force to the soft magnetic layer as the backing layer.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. 1 to 3 show an embodiment of a magnetic recording medium for perpendicular magnetic recording according to the present invention. As shown in FIG. 1, the magnetic recording medium A of the present embodiment has a characteristic that can maintain the magnetization direction vertically upward or downward for each magnetic domain A0 according to the external magnetic field H applied perpendicularly from the magnetic head B. It is what you have. The magnetic recording medium A includes a substrate layer 1, a first soft magnetic layer 2, a nonmagnetic layer 3, a second soft magnetic layer 4, an intermediate layer 5, and a magnetic recording layer in order from the distance from the magnetic head B. 6 and a protective layer 7. The first and second soft magnetic layers 2 and 4 and the nonmagnetic layer 3 are provided as a backing layer 10 for the magnetic recording layer 6.

  The substrate layer 1 is made of, for example, glass of a nonmagnetic material and has a thickness of about 0.6 mm, for example.

The first soft magnetic layer 2 and the second soft magnetic layer 4 are made of a soft magnetic material having the same composition and the same thickness and having a composition of Co80Zr10Nb10. The thickness t of each of the first and second soft magnetic layers 2 and 4 is, for example, about 25 nm. Each of the first and second soft magnetic layers 2 and 4 has a saturation magnetization Ms of about 900 emu / cc (= 10 ³ A / m), for example, and about 25 Oe (= 10 ³ / 4πA / m), for example. Has an anisotropic magnetic field Hk. As shown in FIG. 2A, the first and second soft magnetic layers 2 and 4 have a magnetization direction in a state where the external magnetic field H does not act (broken arrows for the first soft magnetic layer 2). The second soft magnetic layer 4 is indicated by solid arrows) in opposite directions in the layer plane. Such first and second soft magnetic layers 2 and 4 function as a path (magnetic path) of the magnetic flux applied from the magnetic head B, and serve as the backing layer 10 for returning the magnetic flux to the magnetic head B again. To play a role. The soft magnetic material may be, for example, a soft magnetic material having a composition of Fe60Co30B10 and a saturation magnetization of about 1700 emu / cc (= 10 ³ A / m).

The nonmagnetic layer 3 is made of, for example, Ru (ruthenium), which is a nonmagnetic material. The thickness of the nonmagnetic layer 3 is considerably smaller than that of the first and second soft magnetic layers 2 and 4. Are formed between the soft magnetic layers 2 and 4. According to the nonmagnetic layer 3 having an extremely thin thickness, an exchange magnetic field Hs is generated between the first and second soft magnetic layers 2 and 4, and as a result, the magnetization directions are easily aligned in one direction. Such a nonmagnetic layer 3 is provided in order to give the backing layer 10 the desired magnetic properties. The exchange magnetic field Hs is generally expressed by the following equation, where σ is the exchange coupling energy by the nonmagnetic layer 3, t is the thickness of the first and second soft magnetic layers 2 and 4, and Ms is their saturation magnetization. Defined. The exchange coupling energy σ of the nonmagnetic layer 3 is about 0.5 erg / cm ² (= 10 ⁻³ J / m ² ).

  The intermediate layer 5 has, for example, a multilayer structure of a Pt (platinum) layer 5A as a base and a nonmagnetic Ru layer 5B. The Pt layer 5A has a thickness of about 5 nm, and the Ru layer 5B has a thickness of about 20 nm. Such an intermediate layer 5 is provided in order to improve the crystal orientation of the magnetic recording layer 6.

The magnetic recording layer 6 is made of, for example, a magnetic material having a composition of Co77Cr10Pt13-SiO ₂ 11 (CCP-SiO ₂ ) and has a thickness of, for example, about 17 nm. This magnetic recording layer 6 has a saturation magnetization of about 520 emu / cc (= 10 ³ A / m), for example, and has a vertical coercive force larger than a horizontal coercive force. 2 kOe (= 10 ⁶ / 4πA / m). In such a magnetic recording layer 6, the magnetization direction is aligned vertically upward or downward for each magnetic domain A0, and magnetic recording is thereby performed.

  The protective layer 7 is made of, for example, a carbon layer and has a thickness of about 3 nm. Such a protective layer 7 has a role of preventing the magnetic head B from coming into contact with the magnetic recording layer 6.

  Next, the magnetic properties of the magnetic recording medium A, particularly the magnetic properties of the backing layer 10 composed of the first and second soft magnetic layers 2 and 4 and the nonmagnetic layer 3 will be considered.

First, as shown in FIG. 2A, the external magnetic field H is not applied to the backing layer 10, and the magnetization directions of the first and second soft magnetic layers 2 and 4 are in the plane of the layer. The states are opposite to each other and along the easy magnetization axis direction Fe. This state is the initial state. Within the layer surface of the backing layer 10, a hard magnetization axis direction Fd exists in a direction perpendicular to the easy magnetization axis direction Fe. For the first soft magnetic layer 2, as indicated by the dashed arrow in the figure, the saturation magnetization is Ms ₁ , and the initial magnetization direction is rightward along the easy axis direction Fe. For the second soft magnetic layer 4, the saturation magnetization is Ms ₂ , and the initial magnetization direction is leftward along the easy magnetization axis direction Fe, as indicated by the solid line arrow in FIG.

Here, as shown in FIG. 2A, the angle that the external magnetic field H arbitrarily forms with respect to the easy axis direction Fe is θ ₀ , and the saturation magnetizations Ms ₁ and Ms ₂ are arbitrary with respect to the external magnetic field H. When the formed angles are θ ₁ and θ ₂ , the magnetic energy E of the backing layer 10 is given by the following formula (2).

In the above formula (2), Ku is the magnetic anisotropy energy (magnetic anisotropy constant) per unit volume of the first and second soft magnetic layers 2 and 4, and Ms is Ms = Ms _1. = Ms ₂ . On the right side of Equation (2), the first term represents magnetic anisotropy energy, the second term represents Zeeman energy due to the external magnetic field H, and the third term represents exchange coupling energy.

  As shown in FIG. 2B, when an external magnetic field H acts on the backing layer 10 in the initial state along the hard axis direction Fd, as shown in FIG. For the case where the external magnetic field H acts along the easy magnetization axis direction Fe, the magnetization process of the first and second soft magnetic layers 2 and 4 is simulated based on a mathematical model.

First, it will be examined what happens to the magnetization process when an external magnetic field H acts in the hard axis direction Fd. In this case, the angle theta ₀ of the external magnetic field H, θ ₀ = π / 2, and the saturation magnetization Ms _1, the angle theta ₁ of Ms _2, theta _{2 is, θ 1 = -π / 2,} θ 2 = π / 2 finally becomes θ ₁ = 0 and θ ₂ = 0. The first and second soft magnetic layers 2 and 4 have the same magnetic characteristics and have saturation magnetizations Ms ₁ and Ms ₂ (= Ms) symmetrically with respect to the external magnetic field H in the hard axis direction Fd. Since it is considered to be oriented, θ ₁ = −θ ₂ = θ. When Expression (2) is modified based on the condition of θ ₀ = π / 2, θ ₁ = −θ ₂ = θ, the following is obtained.

  Next, the above equation (3) is differentiated by θ, and the conditions under which the magnetic energy E takes an extreme value are examined.

  Here, the anisotropic magnetic field Hk is generally defined by Hk = 2 Ku / Ms (5). Based on this formula (5) and formula (1), the above formula (4) can be transformed into the following formula (6).

  As a result, the condition that the magnetic energy E takes an extreme value is given by the following equation (7) for the equation (6) to be zero.

  In consideration of the initial state and the equation (3), the magnetic energy E takes a minimum value when the equation solution cos θ = H / (Hk + σ / tMs) in the equation (7).

Here, when the magnetization in the hard axis direction Fd obtained by synthesizing the saturation magnetization Ms of the first and second soft magnetic layers 2 and 4 is M _total , this magnetization M _total is expressed by the following equation (8). Can do.

  In order to investigate the magnetization process, the mathematical solution of equation (7) is substituted into equation (8). As a result, the following equation (9) is derived.

As a result, as shown in FIG. 3, the magnetization curve MHd representing the magnetization process of the backing layer 10 when the external magnetic field H acts in the hard axis direction Fd is M _total = 0 to M _total = 2Ms (M / Ms = 1) until it reaches approximately 1 / (Hk + σ / tMs), and when the external magnetic field becomes Ha, M / Ms = 1 and the magnetization is saturated. The external magnetic field Ha at the time when the magnetization is saturated is obtained by substituting M _total = 2Ms into the equation (9) and further substituting Hs = σ / tMs in the equation (1), so that Ha = Hk + Hs (10) Become. This means that the external magnetic field Ha that saturates the magnetization by the amount of the exchange magnetic field Hs is larger than the anisotropic magnetic field Hk when the backing layer is a single layer.

The above-mentioned external magnetic field Ha is obtained by substituting specific numerical values into the equation (9). For example, Hk = 25 Oe (= 10 ³ / 4πA / m), Ms = 900 emu / cc (= 10 ³ A / m), t = 25 nm, σ = 0.5 erg / cm ² (= 10 ⁻³ J / m ²⁾ ), The external magnetic field Ha is Ha = 25 + 222 = 247 Oe (= 10 ³ / 4πA / m). This generally agrees with the results obtained from actual experiments.

Next, the magnetization process will be examined when an external magnetic field H acts on the easy axis direction Fe. In this case, the angle θ ₀ formed by the external magnetic field H is θ ₀ = 0, and the angles θ ₁ and θ ₂ formed by the saturation magnetizations Ms ₁ and Ms ₂ are finally determined from θ ₁ = −π and θ ₂ = 0. θ ₁ = 0 and θ ₂ = 0. Substituting θ ₀ = 0 into equation (2) yields the following equation (11).

Next, the above equation (11) is partially differentiated by θ ₁ and θ ₂ to examine conditions under which the magnetic energy E takes an extreme value.

  The following equation (14) is derived from the above equations (12) and (13).

In Equation (14), in order for the left side and the right side to be equal, θ ₁ = θ ₂ = 0, θ ₁ = θ ₂ ,
A condition such as θ ₁ = −θ ₂ can be considered. Originally, the minimum value and the maximum value should be determined. However, when θ ₁ = θ ₂ , it is clear that the exchange coupling energy σ due to antiferromagnetic coupling is maximized, so θ ₁ = −θ Investigate the case of ₂ . Substituting θ ₁ = −θ ₂ into equation (12), the following equation (15) is derived.

Next, the transition magnetic field from the initial state θ ₁ = −π, θ ₂ = 0 to the state (θ ₁ = −θ ₂ ) of the equation (15) is examined. The energy difference E _d between the magnetization energy E ₀ in the initial state and the magnetization energy E _A when the transition magnetic field is reached is given by the following equation (16) from the equation (11).

  When the equation (16) becomes 0, the magnetization state transitions, and therefore the condition that the equation in parentheses in the equation (16) becomes 0 is obtained from the equation (15).

As a result, as shown in FIG. 3, the magnetization curve MHe representing the magnetization process of the backing layer 10 when the external magnetic field H acts in the easy axis direction Fe is such that the external magnetic field H is larger than Hc in Expression (17). It shows a tendency as shown by the formula (15) under the following conditions. That is, Hc becomes a coercive force. The change in magnetization at this time is as follows. Here, when the magnetization in the easy axis direction Fe obtained by combining the saturation magnetization Ms of the first and second soft magnetic layers 2 and 4 is M _total , this magnetization M _total is expressed by the following equation (18). Can do.

  In order to examine the change in magnetization, the equation (15) is substituted into the equation (18).

  Thus, when the external magnetic field H acts in the easy axis direction Fe, the external magnetic field Hb at the time when the magnetization is saturated becomes Hb = Hs−Hk (20) based on the equation (19). This means that the magnetization is saturated only by subtracting the anisotropic magnetic field Hk from the exchange magnetic field Hs, because the magnetic energy is reduced in the easy axis direction Fe.

Here, the initial state θ ₁ = −π, transition from θ ₂ = 0 to θ ₁ = −θ ₂ , and finally the condition that θ ₁ = θ ₂ = 0 is as follows.

From the condition of the above equation (21), it is considered that when Hs <2Hk, magnetization transition occurs from H ₁ = −π and θ ₂ = 0 to θ ₁ = θ ₂ = 0 when H = Hk.

The above equation (1) is substituted into equation (21), and the condition of the exchange coupling energy σ is examined based on specific numerical values. For example, when Hk = 25 Oe (= 10 ³ / 4πA / m), Ms = 900 emu / cc (= 10 ³ A / m), and t = 25 nm, the initial state θ ₁ = −π, θ ₂ = 0 to θ _The condition for transitioning to ₁ = −θ ₂ and finally θ ₁ = θ ₂ = 0 is σ> 0.113 erg / cm ² (= 10 ⁻³ J / m ² ). As described above, since the exchange coupling energy σ is σ = 0.5 erg / cm ² (= 10 ⁻³ J / m ² ), this satisfies the condition for causing the magnetization transition.

Further, when the coercive force Hc is obtained from the equation (17), Hc = 70.2 Oe (= 10 ³ / 4πA / m).

Further, by substituting the equation (17) into the equation (19), the value of the relative magnetization Ma / Ms when the initial state θ ₁ = −π and θ ₂ = 0 to θ ₁ = −θ ₂ is obtained is obtained. The relative magnetization Ma / Ms is about Ma / Ms = 0.36.

Further, when the external magnetic field Hb at the time when the magnetization is saturated is obtained based on the equation (20), the external magnetic field Hb is about Hb = 197.2 Oe (= 10 ³ / 4πA / m).

  In summary, the magnetization curves MHd and MHe representing the magnetization process of the backing layer 10 when the external magnetic field H acts on each of the hard axis direction Fd and the easy axis direction Fe are as follows.

  Therefore, according to the magnetic recording medium A of the present embodiment, since the nonmagnetic layer 3 having an appropriate thickness is provided between the first and second soft magnetic layers 2 and 4, the first and second soft magnetic layers 2 and 4 are provided. An exchange magnetic field Hs due to antiferromagnetic coupling can be generated between the soft magnetic layers 2 and 4 with an appropriate strength, thereby effectively giving the backing layer 10 the desired coercive force Hc and effectively causing the WATER phenomenon. Can be suppressed.

1 is a configuration diagram showing an embodiment of a magnetic recording medium for perpendicular magnetic recording according to the present invention. FIG. 2 is a reference diagram for analyzing magnetic characteristics of the magnetic recording medium shown in FIG. 1. It is explanatory drawing for demonstrating the magnetic characteristic of the magnetic recording medium shown in FIG.

Explanation of symbols

A magnetic recording medium for perpendicular magnetic recording 2 first soft magnetic layer 3 nonmagnetic layer 4 second soft magnetic layer 6 magnetic recording layer 10 backing layer

Claims (3)

A magnetic recording medium for perpendicular magnetic recording comprising a plurality of soft magnetic layers as a backing layer for a magnetic recording layer,
A magnetic recording medium for perpendicular magnetic recording, wherein a nonmagnetic layer is provided between the plurality of soft magnetic layers so as to generate a coercive force having a desired strength.   The plurality of soft magnetic layers have the same composition and the same thickness, and are formed so that magnetization directions in a state where an external magnetic field does not act are opposite to each other in a layer plane. The magnetic recording medium for perpendicular magnetic recording as described. The thickness of the nonmagnetic layer is such that the coercive force is Hc, the exchange magnetic field strength generated between the plurality of soft magnetic layers is Hs, and the anisotropic magnetic field strength of the soft magnetic layer is Hk. The magnetic recording medium for perpendicular magnetic recording according to claim 1, wherein the magnetic recording medium is set so that the following expression is satisfied.

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