TWI713985B - Perpendicular magnetic recording medium - Google Patents

Abstract

The perpendicular magnetic recording medium of the present invention has a granular layer 2 and a cap layer 3 as layers constituting at least a part of the recording layer 1. The granular layer 2 contains a metal oxide as a non-magnetic body, and the magnetic body is dispersed in the non-magnetic body, The cap layer 3 is formed on the particle layer 2 and does not contain metal oxides. The oxide phase of the boundary part of the particle layer directly below the cap layer 3 and the cap layer contains selected from Zn, W, Mn, Fe And at least one of Mo.

Description

Perpendicular magnetic recording medium

The present invention relates to a perpendicular magnetic recording medium having a granular layer and a cap layer as layers constituting at least a part of the recording layer, the granular layer having magnetic properties dispersed in a non-magnetic body containing a metal oxide The cap layer is formed on the particle layer and does not contain metal oxides. In particular, a technology that can help improve the reversal magnetic field distribution (SFD) required for high-density recording is proposed.

In hard disk drives, the perpendicular magnetic recording method in which the recording surface is magnetically recorded in the vertical direction has been put into practical use. Compared with the previous in-plane magnetic recording method, this method can achieve high-density recording and is therefore widely used. use.

The perpendicular magnetic recording medium is generally constructed by sequentially laminating a soft magnetic layer, an intermediate layer, and a recording layer on a substrate such as aluminum or glass. Among them, the recording layer has a granular layer in the lower part, and the granular layer has a non-magnetic body of a metal oxide such as SiO2 dispersed in a magnetic body such as a Co-Pt-based alloy containing Co as a main component. As a result, the above-mentioned metal oxide as a non-magnetic material in the recording layer precipitates between the grains of magnetic particles of a magnetic material such as a Co alloy oriented in the vertical direction, and the magnetic interaction between the magnetic particles is reduced, resulting in The noise characteristics of the camera have been improved, and a high recording density has been achieved. As a technique related to this, there is a technique described in Patent Document 1 and the like.

In addition, for example, as described in Patent Document 2, each layer of such a magnetic recording medium It is usually formed by sputtering using a sputtering target with a prescribed composition corresponding to the layer and using a magnetron sputtering device.

Prior art literature Patent literature

Patent Document 1: Japanese Patent No. 4021435; Patent Document 2: Japanese Patent No. 5960287.

The recording layer of the perpendicular magnetic recording medium as described above generally has a cap layer in addition to the granular layer. The cap layer is formed on the granular layer, does not contain metal oxides, and is mainly composed of a magnetic body. Based on this, the particle separation property of the particle layer in which the magnetic particles are magnetically separated due to the metal oxide is used to achieve low noise, and at the same time, the cap layer that retains the interaction between the magnetic particles due to the absence of the metal oxide Appropriate interaction between magnetic particles is provided to the particle layer to ensure the ease of writing of the medium, reduction of SFD, thermal stability, etc.

However, in order to form the recording layer of such a perpendicular magnetic recording medium, when the cap layer is formed by sputtering or the like on the particle layer, due to the wettability between the metal oxide in the particle layer and the metal of the cap layer The film of the cap layer grows selectively in the part of the particle layer where there is no metal oxide. As a result, the initial growth of the thin film of the cap layer becomes non-uniform following the morphology of the particle layer containing the metal oxide. Therefore, there is the following problem: even if the cap layer with a predetermined thickness is formed, the magnetic field distribution (SFD: switching field distribution) is reversed. ) Also did not improve. On the other hand, when a thick cap layer is formed, although the SFD is improved, the distance between the magnetic head and the center of the medium becomes larger, and the resolution decreases. In addition, the exchange bond between the magnetic particles becomes larger due to the thick cap layer. The cluster size increases and the recording density cannot be increased.

The present invention aims to solve the above-mentioned problems of existing perpendicular magnetic recording media, and its object is to provide a perpendicular magnetic recording medium in which a cap layer is uniformly laminated on the granular layer of the recording layer, thereby effectively improving Reverse magnetic field distribution (SFD).

As a result of intensive research, the inventor found that the boundary between the granular layer directly below the cap layer and the cap layer in the recording layer contains a prescribed metal oxide, and the metal oxide contains more Co. The cap layer has good wettability, and the cap layer is also laminated on the non-magnetic part of the granular layer in the same manner as on the magnetic part of the granular layer from the early stage of its growth. As a result, the cap layer is on the granular layer A uniform cap layer is formed. In addition, from the viewpoint of effectively separating the magnetic particles, when a predetermined metal oxide is used as the metal oxide in the boundary portion of the particle layer, the magnetic separation required for the magnetic particles in the particle layer can be achieved.

Based on this finding, the perpendicular magnetic recording medium of the present invention has a granular layer and a cap layer as layers constituting at least a part of the recording layer, the granular layer contains a metal oxide as a non-magnetic material, and the magnetic material is dispersed in the non-magnetic material. The cap layer is formed on the above-mentioned particle layer and does not contain metal oxides. The oxide phase of the boundary part of the particle layer directly below the cap layer and the cap layer contains selected from among Zn, W, Mn, Fe and Mo At least one of them.

In the perpendicular magnetic recording medium of the present invention, the oxide phase of the boundary portion of the granular layer preferably contains at least Zn in the metal.

In addition, in the perpendicular magnetic recording medium of the present invention, the oxide phase of the boundary portion of the granular layer may further contain at least one of B and Si, and the oxide phase of the boundary portion of the granular layer may further contain Ti.

The perpendicular magnetic recording medium of the present invention preferably has a layer that does not contain Zn in the remaining part of the granular layer except for the boundary part.

In this case, it is further preferred that the remaining part of the particle layer contains selected from Si, B and Ti The oxide of at least one element in the above is used as the oxide phase, and the total content of the oxide of the remaining part of the oxide phase is 20 vol.% to 50 vol.%.

In addition, in the perpendicular magnetic recording medium of the present invention, it is preferable that the oxide phase of the boundary portion of the particle layer contains Zn, and the Zn content of the oxide phase is 3 at% or more.

Furthermore, in the perpendicular magnetic recording medium of the present invention, it is preferable that the thickness of the above-mentioned boundary portion accounts for 3% to 50% of the thickness of the entire particle layer in the stacking direction of the recording layer.

In addition, here, the magnetic particles of the entire particle layer including the above-mentioned boundary portion may contain Co as a main body as a magnetic body, and may contain at least one metal selected from Pt, Ru, and Cr. The magnetic body may have a so-called ECL (Exchange Coupling Layer) cut off by a non-magnetic layer mainly composed of Co or Ru in the vertical direction.

In addition, the cap layer is mainly composed of Co, and may also contain at least one element selected from Cr, Pt, and B.

Furthermore, the perpendicular magnetic recording medium of the present invention preferably has a thickness of the cap layer of 1 nm to 3 nm in the stacking direction of the recording layer.

According to the perpendicular magnetic recording medium of the present invention, since the oxide phase of the boundary between the granular layer directly below the cap layer and the cap layer contains the above-mentioned metal, the cap layer also contains the metal in the granular layer from the beginning of the growth of the cap layer. The oxide phase is grown on the non-magnetic part, so the cap layer is uniformly laminated on the particle layer, thereby improving the reversal magnetic field distribution (SFD).

1: Recording layer

2: granular layer

2a: boundary part

2b: remaining part

3: cover layer

4a: Oxide phase

4b: Metallic phase

tg: the overall thickness of the particle layer

tb: the thickness of the boundary part

tc: thickness of the cap layer

Figure 1 is a cross-sectional view of the recording layer along the stacking direction, which schematically shows the recording layer of the perpendicular magnetic recording medium according to one embodiment of the present invention.

Fig. 2 is a cross-sectional view of the recording layer along the stacking direction, which schematically shows the recording layer of a conventional perpendicular magnetic recording medium.

Fig. 3 is a graph showing the variation of Ra as the film thickness tc of the cap layer increases during sputtering in Test Example 1 of the working example.

Fig. 4 is a graph showing the change in -Hn as the film thickness tc of the cap layer increases during sputtering in Test Example 1 of the working example.

FIG. 5 is a graph showing the relationship between the Zn content in Test Example 3 of the working example and the film thickness of the cap layer having Ra of the cap layer less than 5 Å.

Figure 6 is a graph showing the relationship between the Zn content and the film thickness of the cap layer in which -Hn is positive in Test Example 3 of the working example.

Hereinafter, embodiments of the present invention will be described in detail.

The perpendicular magnetic recording medium of one embodiment of the present invention includes a recording layer. As illustrated in FIG. 1, the recording layer 1 has a granular layer 2 and a cap layer 3 as layers constituting at least a part thereof, and the granular layer 2 contains a metal oxide as A non-magnetic body and a magnetic body dispersed in the above-mentioned non-magnetic body, the cap layer 3 is formed on the particle layer 2 and does not contain a metal oxide. Therefore, in the recording layer 1 of this embodiment, the granular layer 2 includes an oxide phase 4a composed of a non-magnetic body and a metal phase 4b composed of a magnetic body, and the cap layer 3 does not contain a metal oxide and is only defined by Metal composition.

In addition, the perpendicular magnetic recording medium may, for example, laminate a substrate, a soft magnetic layer, an intermediate layer, and the recording layer 1 in this order. The parts other than the recording layer 1 may be the same as in the past, so the description is omitted here. In addition, although the recording layer 1 of the present embodiment includes the granular layer 2 and the cap layer 3, depending on the situation, it may also include an Onset layer, an ECL layer, etc., which are non-magnetic or have a small magnetic moment.

(Cover)

The cap layer 3 does not contain a metal oxide and is composed only of a magnetic metal. Specifically, such a metal includes Co as a main component and at least one element selected from Cr, Pt, and B.

The metal constituting the cap layer 3 is typically composed mainly of Co and Pt, and may contain one or more elements selected from Cr and B as necessary. The cap layer 3 is usually an alloy mainly composed of CoCrPtB.

In this embodiment, as described below, during the film formation of the cap layer 3, the cap layer 3 can be uniformly laminated on the particle layer 2 from the beginning of the film formation, so the thickness tc of the cap layer 3 will not reach the desired level. Need more than the thickness, can effectively improve the reversal magnetic field distribution (SFD). The thickness tc of the cap layer 3 is preferably set to 3% to 30% as a percentage of the thickness tg of the entire particle layer 2. Specifically, it is appropriate to set the thickness tc of the cap layer 3 to 0.5 nm to 3 nm.

(Grain layer)

Although the entire particle layer 2 contains the non-magnetic metal oxide phase 4a and the magnetic metal phase 4b, it is important to observe the particle layer 2 in the stacking direction of the recording layer 1, as shown in the first As shown in the figure, it is composed of at least two layers including a boundary portion 2a located directly below the cover layer 3 and a remaining portion 2b located below the boundary portion 2a other than the boundary portion 2a. The boundary portion 2a and the remaining portion 2b have different metal oxides constituting the oxide phase 4a thereof.

Specifically, the oxide phase 4a of the boundary portion 2a contains at least one selected from Zn, W, Mn, Fe, and Mo, and preferably contains Zn. Here, the oxide contained in the boundary portion 2a is mainly ZnO.

Based on this, when the cap layer 3 is formed by sputtering on the particle layer 2, the metal constituting the metal oxide-free cap layer 3 and the ZnO at the boundary portion 2a of the particle layer 2 show good wettability. Therefore, the constituent metals of the cap layer 3 can be uniformly laminated on the entire particle layer 2 including the oxide phase 4a of the boundary portion 2a from the initial growth stage of the cap layer 3. Thereby, the function of the cap layer 3 is effectively performed, and the reversal magnetic field distribution (SFD) can be improved. In addition, ZnO can effectively separate the magnetic particles of the metal phase 4b of the particle layer 2, so even It is the boundary part 2a of the particle layer 2, and it is possible to ensure the required magnetic separation property substantially the same as the remaining part 2b.

In addition, in the conventional perpendicular magnetic recording medium, as shown in Figure 2, the oxide phase 14a of the particle layer 12 is composed of oxides of metals other than the above-mentioned metals in the entire lamination direction. At 13 o'clock, at the early stage of its growth, the metal of the cap layer 13 is selectively laminated on the metal phase 14b of the particle layer 12 where the metal oxide does not exist. That is, as schematically shown in FIG. 2, in the lower part of the cap layer 13 close to the particle layer 12, the metal of the cap layer 13 has a portion that cannot be laminated due to the excellent crystallinity, so-called epitaxial growth. Therefore, even if the cap layer 13 is formed with a predetermined thickness, it is impossible to improve the reversal magnetic field distribution (SFD). In addition, it is considered that this situation can be prevented by making the cap layer 13 thick enough. However, in this case, the distance between the magnetic head and the center of the medium increases, and the resolution decreases. In addition, the exchange bond between the magnetic particles is due to the thick cap layer 13. If it becomes larger, the size of the magnetic cluster increases, and there are other problems that cannot increase the recording density.

In the embodiment of the present invention shown in Fig. 1, the oxide phase of the boundary portion 2a contains Zn, W, Mn, Fe and/or Mo which are easily wetted with the cap layer 3, and therefore can effectively solve the above-mentioned existing problems .

When the boundary portion 2a of the particle layer 2 contains Zn, its Zn content is preferably set to 3 at% or more. When the Zn content of the boundary portion 2a is less than 3at%, improvement of wettability is hopeless, and it may be difficult for the cap layer to be epitaxially grown on the oxide phase. In addition, when the Zn content of the boundary portion 2a exceeds 25at%, Zn A large amount of it will enter the metal phase, and there is a concern that magnetic anisotropy and crystallinity will decrease.

In order to improve the wettability, the oxide phase of the boundary portion 2a of the particle layer 2 further preferably contains at least one selected from the group consisting of Zn, W, Mn, Fe, and Mo, B and Si to improve amorphous properties, and to improve separation The metallic oxide of Ti. That is, the oxide phase of the boundary portion 2a of the particle layer 2 may also contain only at least one selected from Zn, W, Mn, Fe, and Mo, and in addition, may contain at least one of B and Si, and/ Or Ti.

Observed in the stacking direction of the recording layer, the thickness tb of the boundary portion 2a of the particle layer 2 is It is suitable that the ratio (tb/tg) of the total thickness tg of the particle layer 2 is 3%-50% expressed as a percentage. When the ratio (tb/tg) of the thickness tb of the boundary portion 2a to the overall thickness tg is less than 3%, the uniform film formation effect of the cap layer 3 by ZnO in the boundary portion 2a may not be sufficiently obtained. The ratio (tb/tg) of the thickness tB of the boundary portion 2a to the thickness tg of the entire particle layer 2 is more preferably 3% to 30%.

On the other hand, the oxide phase of the remaining part 2b of the particle layer 2 that does not greatly affect the uniform film formation of the cap layer 3 may contain Zn like the boundary part 2a, but an oxide phase that does not contain Zn is preferred. In addition, it is suitable for the remaining part 2b of the particle layer 2 to be a layer containing not only ZnO but also Zn. This is because when the remaining part 2b of the particle layer 2 contains Zn, there is a fear that the magnetic anisotropy Ku will decrease.

In the remaining part 2b of the particle layer 2, as an oxide phase, an oxide of at least one element selected from Si, B, and Ti may be contained instead of a prescribed metal oxide such as ZnO as described above. The total content of oxides of the remaining part 2b including oxides other than the oxides is preferably 20 vol.% to 50 vol.%. In addition, when the total content of oxides in the remaining part 2b is less than 20vol.%, the separation of the metal phase is insufficient, and the size of the magnetic cluster may become larger, and when it exceeds 50vol.%, the proportion of the metal phase is small and cannot be obtained. Sufficient Ku and magnetic anisotropy, thermal stability or regeneration signal strength may be insufficient. In addition, the volume ratio of the oxide in the film can be obtained by TEM observation.

In addition, the metal phase 4b as the magnetic body of the particle layer 2 is mainly composed of Co, and further contains at least one metal selected from Pt, Ru, and Cr.

Example

Next, the perpendicular magnetic recording medium of the present invention was trial-produced, and its performance was evaluated, so it will be described below. However, the description here is for illustration only, and is not intended to be limited to this.

(Test Example 1)

As Example 1-1, a magnetron sputtering device (C-3010 sputtering system manufactured by CANON ANELVA) was used to sequentially form Cr-Ti (6nm), Ni-W (5nm), and Ru (20nm) on a glass substrate. Co-Pt-SiO ₂ (10nm) film as the lower particle layer (the remaining part of the particle layer) is formed on the obtained article, and a sputtering target containing Co-Pt-ZnO is used on it, and the Ar is 5.0Pa Sputtering at 300W in an environment with a thickness of 3nm was formed as the upper particle layer (the boundary between the particle layer and the cap layer), and then Co-Cr-Pt-B as the cap layer was formed on it (0~8nm) film, each layer is formed. In Example 1-1, the oxide of the upper particle layer contains ZnO.

In addition, as Example 1-2 to Example 1-5, the same film as in Example 1 was formed except that the oxide of the upper particle layer contained WO ₃ , MnO, Fe ₂ O ₃ , and MoO ₃ .

Furthermore, as Comparative Example 1, each layer was formed in the same manner as in Example 1, except that the oxide phase of the upper particle layer contained SiO ₂ .

For the above-mentioned Examples 1-1 to 1-5 and Comparative Example 1, the roughness (Ra) and the inversion start magnetic field (-Hn) relative to the film thickness of the cap layer were measured. Their comparison is shown graphically in Figures 3 and 4. In Figures 3 and 4, SiO ₂ refers to Comparative Example 1, ZnO refers to Example 1-1, WO ₃ refers to Example 1-2, MnO refers to Example 1-3, Fe ₂ O ₃ Refers to Examples 1-4, and MoO ₃ refers to Examples 1-5.

In addition, in Examples 1-1 to 1-5 and Comparative Example 1, the lower particle layer is all 67Co-23Pt-10SiO ₂ (mol%), and the cap layer is all 60Co-10Cr-15Pt-5B (mol%) .

In addition, in Example 1-1, the upper particle layer is 62Co-21Pt-17ZnO (mol%) (ZnO=30vol.%), and in Comparative Example 1, the upper particle layer is 67Co-22Pt-10SiO ₂ (mol%) ) (SiO ₂ =30vol.%). The upper particle layers are as follows: 70Co-23Pt-7WO ₃ (mol%) (WO ₃ =30vol.%) in Example 1-2, 61Co-20Pt-19MnO (mol%) in Example 1-3 (MnO=30vol.%), 68Co-23Pt-10Fe ₂ O ₃ (mol%) in Example 1-4 (Fe ₂ O ₃ =30 vol.%), 62Co-21Pt in Example 1-5 -18MoO ₃ (mol%) (MoO ₃ =30vol.%).

In addition, the roughness (Ra) was measured using an atomic force microscope (AFM) manufactured by SII, and the inversion start magnetic field (-Hn) was measured using a sample vibration magnetometer (VSM) manufactured by Tamagawa Manufacturing Co., Ltd. .

As shown in Figure 3, it can be seen that compared with Comparative Example 1 where the oxide of the upper granular layer is SiO2, the oxide of the upper granular layer is ZnO in Examples 1-1 to 1-5 even though the thickness of the cap layer (tc ) Is thin, and it can also be seen that Ra is sufficiently reduced, so that the upper Co-based cap layer and Zn oxide have good wettability. In addition, it can be seen from Figure 4 that in Examples 1-1 to 1-5, compared with Comparative Example 1 in which the oxide of the upper particle layer is SiO ₂ , the cap layer is thinner in the range d(-Hn)/ dtc is positive, thus obtaining the SFD effect of the cap layer.

(Test Example 2)

As a reference example, 67Co-22Pt-10SiO ₂ (mol%) (SiO ₂ =30vol.%) as a sputtering target containing no Zn and 62Co-21Pt-17ZnO (mol%) as a sputtering target containing Zn were used. ) (ZnO=30vol.%), in the same manner as in Test Example 1, a sample in which a single particle layer of 13 nm was formed after the formation of Ru and the magnetic anisotropy Ku was measured.

In addition, the magnetic anisotropy (Ku) was measured using a magnetic torque meter (TRQ) manufactured by Tamagawa Seisakusho.

When the oxide of the particle layer is SiO ₂ , the Ku value is 6.16×10 ⁶ erg/cc, while when it is ZnO, the Ku value is 5.04×10 ⁶ erg/cc. From this, it can be seen that Ku becomes lower when a sputtering target containing Zn is used. Therefore, the lower particle layer often uses a sputtering target with a high Ku composition. Therefore, it can be considered that it is desirable to have a Zn-free layer in the lower particle layer.

(Test Example 3)

As Examples 3-1 to 3-22, sputtering targets of Co-Pt-ZnO, Co-Pt-SiO ₂ -ZnO, Co-Pt-B ₂ O ₃ -ZnO, and Co-Pt-TiO ₂ -ZnO were used Several prototypes with varying Zn content were manufactured. The composition of each sputtering target is shown in Table 1 for reference.

Table 1

Using each of the above-mentioned trial products, a magnetic film was formed by the same method as in Test Example 1, and the roughness (Ra) relative to the film thickness of the cap layer and the inversion start magnetic field (-Hn) were measured. In addition, the above-mentioned trial product was used for film formation of the upper particle layer of the magnetic film. The relationship between the Zn content and the film thickness of the cap layer whose Ra is less than 5 Å is shown in Figure 5, and the relationship between the Zn content and the film thickness of the cap layer with positive -Hn is shown in Figure 6.

It can be seen from Fig. 5 that in particular, Examples 3-5~3-8, Examples 3-12~3-15, and Examples 3-19~3-22 in which the Zn of the upper granular layer is 3at% or more, even if covered When the layer is thin, it can also be seen that the Ra is sufficiently reduced, and the wettability of the upper Co-based cap layer and Zn oxide becomes better. In addition, it can be seen from Fig. 6 that, in particular, Examples 3-5 to 3-8, Examples 3-12 to 3-15, and Examples 3-19 to 3-22 in which the Zn of the upper particle layer is 3 at% or more, Since the film thickness of the cap layer with positive d(-Hn)/dtc becomes quite thin, by adding Zn, the SFD is further improved by using the thin cap layer.

1: Recording layer

2: granular layer

2a: boundary part

2b: remaining part

3: cover layer

4a: Oxide phase

4b: Metallic phase

tg: the overall thickness of the particle layer

tb: the thickness of the boundary part

tc: thickness of the cap layer

Claims (11)

A perpendicular magnetic recording medium having a granular layer and a cap layer as layers constituting at least a part of the recording layer, the granular layer contains a metal oxide as a non-magnetic body, and a magnetic body is dispersed in the non-magnetic body, The cap layer is formed on the particle layer and does not contain a metal oxide but contains a magnetic metal. The oxide phase of the boundary part of the particle layer directly below the cap layer and the cap layer contains Zn, W , Mn, Fe and Mo at least one. The perpendicular magnetic recording medium described in the first item of the patent application, wherein the oxide phase of the boundary portion of the granular layer is formed by containing Zn. The perpendicular magnetic recording medium described in item 1 or item 2 of the scope of the patent application, wherein the oxide phase of the boundary portion of the granular layer further contains at least one of B and Si. The perpendicular magnetic recording medium described in item 1 or item 2 of the scope of patent application, wherein the oxide phase of the boundary portion of the granular layer is formed by further containing Ti. The perpendicular magnetic recording medium described in item 1 or item 2 of the scope of patent application, wherein a remaining part of the granular layer except the boundary part has a layer that does not contain Zn. The perpendicular magnetic recording medium according to item 5 of the scope of patent application, wherein the remaining part of the granular layer contains an oxide of at least one element selected from Si, B and Ti as an oxide phase, and the remaining part The total content of oxides in the oxide phase is 20 vol.% to 50 vol.%. The perpendicular magnetic recording medium according to item 1 or item 2 of the scope of patent application, wherein the oxide phase of the boundary portion of the granular layer contains Zn, and the Zn content of the oxide phase is 3 at% or more. The perpendicular magnetic recording medium described in item 1 or item 2 of the scope of patent application, wherein, in the stacking direction of the recording layer, the thickness of the boundary portion accounts for the thickness of the entire particle layer The ratio is 3%~50%. The perpendicular magnetic recording medium described in item 1 or item 2 of the scope of the patent application, wherein the entire grain layer including the boundary portion contains at least one selected from Co, Pt, Ru, and Cr as a metal phase Formed of metal. The perpendicular magnetic recording medium described in item 1 or item 2 of the scope of the patent application, wherein the cap layer is formed by containing at least one element selected from Co, Cr, Pt, and B. The perpendicular magnetic recording medium described in item 1 or item 2 of the scope of patent application, wherein the thickness of the cap layer is 1 nm to 3 nm in the stacking direction of the recording layer.

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