JP2003303408A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium wherein each ferromagnetic layer has antiferromagnetic coupling even when the ferromagnetic layer of an AFC medium becomes thick, noise is low, and the influence of thermal fluctuation is suppressed. <P>SOLUTION: This magnetic recording medium is provided with a magnetic recording layer formed through a foundation layer on a substrate. In this case, the magnetic recording layer has at least two ferromagnetic layers antiferromagnetically coupled with each other through a nonferromagnetic layer, and an antiferromagnetic layer is disposed below the magnetic recording layer closest to the foundation layer. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a magnetic recording medium. More specifically, in a multi-layered ferromagnetic recording layer, by forming an antiferromagnetic layer directly below the ferromagnetic layer closest to the underlayer side, thermal information of recorded information can be obtained even at an extremely high recording density. The present invention relates to a magnetic recording medium based on an in-plane recording method, which can obtain stability.

[0002]

2. Description of the Related Art The capacity of a magnetic disk device, which is an external magnetic recording / reproducing device for a computer, has been increasing, and at present, the recording density is remarkably increasing at an annual rate of 100%. The magnetic head of the magnetic recording / reproducing apparatus uses a composite head in which a recording unit (electromagnetic induction type magnetic head) and a reproducing unit (giant magnetoresistive head (GMR head)) are separated. on the other hand,
The magnetic recording medium consists of a recording layer such as CoCrTa or CoCrPt via a Cr underlayer that controls the crystal orientation of the magnetic layer on the substrate.
A medium provided with a Co alloy magnetic layer and a protective layer is used (JP-A-62-257618, JP-A-63-197018). Since the GMR head has a higher reproduction sensitivity than the conventional electromagnetic induction type head, a sufficient reproduction output can be obtained even when the recording bit becomes minute and the leakage magnetic flux decreases. However, since noise is reproduced with high sensitivity together with the signal of the medium, the medium is required to have lower noise than ever before. In order to reduce the medium noise, it is effective to miniaturize the magnetic particles and thin the recording layer. This is because the medium noise is mainly caused by the disorder of the magnetization in the magnetization transition region between the recording bits, so that this region can be narrowed by making the magnetic particles fine and thinning the recording layer. However, the miniaturization of the magnetic particles and the thinning of the recording layer lead to the recorded magnetization thermally fluctuating and being attenuated with time.
In general, the product of the magnetic anisotropy constant K _u and the volume V of the particle divided by the product of the Boltzmann constant k and the temperature T becomes smaller as K _u · V / k · T becomes smaller. It is known to grow (IEEE Trans. Magn. 30 (1994) p4230). To obtain a thermal stability Therefore, it is desirable to use a material having a large K _u, becomes too high coercive force H _c of the medium and too K _u is increased, a problem that can not be recorded by the magnetic head is caused . Therefore, as a means to achieve a high recording density without increasing the K _u, the magnetic recording layer having at least two ferromagnetic layers via a non-ferromagnetic layer are antiferromagnetically coupled to each other is IBM It is proposed in Japanese Patent Application 2000-307398 (P2000-307398). In addition, at the Intermag International Conference in April 2000, Fujitsu and IBM created a medium (Antiferromagnetically-coupling) in which two or three ferromagnetic layers were antiferromagnetically coupled.
The led medium (AFC medium for short) has been shown to have excellent thermal demagnetization and recording / reproducing characteristics. Since then, AFC media have been studied energetically by each company and each institution, and have come to be used in today's magnetic disk devices. Figure 2
FIG. 3 shows a cross-sectional structure diagram and a magnetic moment schematic diagram of a conventional magnetic recording medium when the AFC medium has two ferromagnetic layers. As shown in the figure, the magnetic moment of the first ferromagnetic layer is opposite to the magnetic moment of the lower ferromagnetic layer via the non-ferromagnetic layer. The residual magnetization of the first ferromagnetic layer
When M _r1 , the film thickness is t ₁ , the remanent magnetization of the second ferromagnetic layer is M _r2 , and the film thickness is t ₂ , the product M _r t of the remanent magnetization and the film thickness of the entire recording layer is given by the following equation. Become.

[0003]

[Equation 1] Therefore, since M _r t is smaller than that in the single-layer medium including only the first ferromagnetic layer, noise is drastically reduced. Further, since the volume of the particles of the recording layer that contributes to the thermal stability is the total volume of the particles that are antiferromagnetically coupled, the thermal stability is higher than that of the single-layer medium including only the first ferromagnetic layer. Of. For the above reasons, a medium suitable for ultrahigh recording density can be achieved.

[0004]

As described above, the AFC medium has been proposed and is now commercialized as a means for improving the thermal demagnetization characteristics without increasing the anisotropy constant K _u . However, it is considered difficult to achieve a recording density of 100 Gb / in ² or more even with an AFC medium. that is,
This is because further miniaturization of magnetic particles is essential to obtain the required S / N ratio (signal to noise ratio). As the grain size becomes smaller, in order to ensure thermal stability, the second ferromagnetic layer must be increased simultaneously with the increase in the first ferromagnetic layer in order not to increase M _r t. However, the antiferromagnetic interface coupling energy density J _ex due to the non-ferromagnetic layer has a limit, and the coupling magnetic field H generated by the second magnetic layer due to J _ex is
_As can be seen from the following equation, _ex becomes smaller in inverse proportion to the film thickness t ₂ of the second ferromagnetic layer.

[0005]

[Equation 1] Therefore, there arises a problem that the first ferromagnetic layer and the second ferromagnetic layer do not make antiferromagnetic coupling.

[0006]

The present invention provides a magnetic recording medium having a magnetic recording layer formed on a substrate via an underlayer, wherein the magnetic recording layers are antiferromagnetic with each other via a non-ferromagnetic layer. It is characterized by having at least two ferromagnetic layers that are magnetically coupled and having an antiferromagnetic layer provided under the ferromagnetic layer closest to the underlayer. By providing the above-mentioned antiferromagnetic layer, even if the ferromagnetic layer of the AFC medium is thickened and the antiferromagnetic coupling magnetic field is lowered, it is possible to help the respective ferromagnetic layers to couple antiferromagnetically. it can. As a result, it is possible to provide a magnetic recording medium that has low noise and can suppress the influence of thermal fluctuation.

The reason for providing the antiferromagnetic layer will be described with respect to a medium composed of two ferromagnetic layers. FIG. 3 is a schematic diagram showing the relationship between the magnetization in the conventional medium and the magnetic field applied to the second ferromagnetic layer. Here, the protective layer, the base layer and the substrate are omitted from the drawing. When the magnetic field is applied to the medium, the two ferromagnetic layers face the same direction (to the right of the paper), but Fig. 3- (a)
After removing the magnetic field, if the second ferromagnetic layer is thin, the magnetizations of the first and second ferromagnetic layers are both antiparallel.
(b). However, when the thickness of the second ferromagnetic layer becomes large and the antiferromagnetic coupling magnetic field H _ex due to the non-ferromagnetic layer between the ferromagnetic layers becomes extremely weak, as shown in FIG. In the structure, the magnetizations of the first and second ferromagnetic layers remain substantially parallel. On the other hand, in the present invention, as shown in the schematic view of FIG. 4, an antiferromagnetic layer is provided under the second ferromagnetic layer, and the magnetization of the antiferromagnetic layer is laminated in the radial direction as shown in the figure. . Fig. 4- (a) is a cross-sectional view of the medium taken along the circumferential direction, Fig. 4- (b) is a plan view of the medium seen from directly above, and Fig. 4- (c) is taken along the radial direction. FIG. In general, when two types of magnetic materials are in contact, their magnetizations tend to rotate in parallel (or antiparallel), so as shown in Figure 4- (b), The magnetization 12- (a) of the magnetic layer is slightly tilted in the radial direction from the circumferential direction. As a result, even when H _ex is very weak, the magnetization is reversed in the opposite direction as shown in Fig. 12- (b). That is, the provision of the antiferromagnetic layer has an effect of helping the first and second ferromagnetic layers become antiparallel even when H _ex is very weak.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Example 1 The inventors of the present invention conducted a Landau-Lifsit test in order to study an AFC medium having an antiferromagnetic layer.
The recording magnetization was calculated by computer simulation using the s-Gilbert equation, and the change over time of the reproduction output was calculated using the Monte Carlo method. FIG. 1 is a sectional structural view of the medium of the present invention. The magnetic recording medium is formed on a disk, and when the drawing is a sectional view taken along the circumferential direction, the depth direction is the radial direction. The medium is formed by laminating an underlayer 2, then an antiferromagnetic layer 3, a second ferromagnetic layer 4, a non-ferromagnetic layer 5, a first ferromagnetic layer 6, and a protective layer 7 in this order on a disk substrate 1. Has been done. In the calculation, the substrate, the underlayer, and the protective layer are not necessary, and thus the omitted model was used. Further, since the antiferromagnetic layer plays a role of applying a magnetic field in the radial direction of the second ferromagnetic layer, the magnetic field applied in the radial direction of the second ferromagnetic layer is added with the magnetic field applied by the antiferromagnetic layer. And calculated. Table 1
Table 2 shows the magnetic characteristics of the medium, and Table 2 shows the R / W conditions. The diameter of the particles is 10 nm, the magnetic properties of the first ferromagnetic layer are constant,
The calculation was performed by changing the magnetic characteristics and the film thickness of the second ferromagnetic layer. The antiferromagnetic interface coupling energy density J _ex by the non-ferromagnetic layer was studied from 0 to 0.6 × 10 ^-3 J / m ² .

[0009]

[Table 1]

[Table 2] Figure 5 shows the MH when a magnetic field is applied in the radial direction of the medium when 4 kA / m is applied from the antiferromagnetic layer to the second ferromagnetic layer.
It is an example of a loop characteristic. M _s2 = 0.5 T, K _u2 = 1.7 × 10 ⁵ J /
m ³ The magnetic field was applied for 24 minutes while the magnetic field was reduced from 800 kA / m to −800 kA / m to obtain the magnetization. Then −800
The magnetic field was similarly applied for 24 minutes while increasing the magnetic field from kA / m to 800 kA / m to obtain the magnetization. Figure 5- (a) is the MH loop for the entire medium. It can be seen that the MH loop produces a step in the middle of the loop. This is because the second ferromagnetic layer receives an exchange coupling magnetic field from the non-ferromagnetic layer and is inverted before the first ferromagnetic layer. That is, the center of the step represents the position of the magnetic field at which the magnetization is zero in the second ferromagnetic layer. Figure 5- (b)
This is a curve obtained by first-order differentiation of the MH loop with respect to the magnetic field. The solid line in the figure is the derivative curve when a magnetic field is applied from 800 kA / m to -800 kA / m, and the dotted line is the derivative curve when a magnetic field is applied from -800 kA / m to 800 kA / m. Two peaks H _1PN and H _{1NP from the figure}
Are observed, which are considered to correspond to the magnetic field when the magnetization of the second ferromagnetic layer becomes 0, respectively. From the figure, 800 kA / m
From -800 kA / m, H _1PN = 104 kA / m, −80
H _1NP = − 112 kA when applied from 0 kA / m to 800 kA / m
became / m. Fig. 6- (a) is the MH loop extracted from the MH loop of Fig. 5- (a), only the MH loop of the second ferromagnetic layer.
(b) is an enlarged view of the MH loop shown in FIG. 6- (a). From this, when an external magnetic field is applied from 800 kA / m to −800 kA / m,
The magnitude of the magnetic field where the MH loop crosses the line with zero magnetization is H _1PN = 1
04 kA / m, H when applied from −800 kA / m to 800 kA / m
_{1N P} = −112 kA / m, which was in agreement with the peak value in Figure 5- (b). _Further, the absolute values of H _1PN and H _1NP differ from each other due to the influence of the magnetic field applied from the antiferromagnetic layer to the second ferromagnetic layer. That is, when applied from 800 kA / m to −800 kA / m, the antiferromagnetic coupling magnetic field of −108 kA / m by the non-ferromagnetic layer is applied to the second ferromagnetic layer, so that the magnetization is the first Although the magnetization is reversed in the quadrant, the magnetic field from the antiferromagnetic layer of 4 kA / m is applied, and the magnetization reversal is delayed accordingly. Conversely, when a magnetic field is applied from −800 kA / m to 800 kA / m, the reversal of magnetization is accelerated by the magnetic field of 4 kA / m applied from the antiferromagnetic layer to the second ferromagnetic layer. That is,
It was found that both H _1PN and H _1NP were about 4 kA / m smaller than in the case without the antiferromagnetic layer. Therefore, when H _1PN and H _1NP are obtained, and the magnetic field imprinted from the antiferromagnetic layer to the second ferromagnetic layer is defined as H _y , the following equation is obtained.

[0010]

[Equation 2] The actual measurement of the MH loop is generally performed using the VSM (vibrating sample magnetometer) or the Kerr effect. Therefore, although only the MH loop of the entire medium can be obtained, as described above,
The MH loop creates a step in the middle of the loop, and the center and the second
The magnetic fields at which the magnetization of the ferromagnetic layer of 0 becomes 0 coincide. Therefore,
The magnetic field applied from the antiferromagnetic layer to the second ferromagnetic layer can be estimated from the peak obtained by first-order differentiating the entire MH loop. FIG. 7 shows the change over time in the reproduction output (normalized by the reproduction output 10 b seconds after recording) when the second magnetic layer thickness is 6 nm and no antiferromagnetic layer is added. here,
The saturation magnetization M _s2 of the second ferromagnetic layer is the same as that of the first ferromagnetic layer.
0.5 T, Anisotropy constant K _u2 is the same as the first ferromagnetic layer 2.35 × 10
^{It is 5} J / m ³ . The exchange coupling energy of the non-ferromagnetic layer was 0.15 × 10 ⁻³ J / m ² . From this, 10 years from 10 seconds after recording (3.1536 × 10 ⁸ seconds) elapses and playback output 10%
Decrease. When converted to the average output reduction rate when the time increases by one digit, it becomes 1.4% / decade. Hereinafter, this is defined as a reproduction output reduction rate as an index of thermal demagnetization. FIG. 8 shows the magnetic field applied from the antiferromagnetic layer to the second ferromagnetic layer and the reproduction output reduction rate after 10 years. The vertical axis is when there is no antiferromagnetic layer (H _y =
The value was normalized by the reproduction output reduction rate of 0 kA / m). Therefore, if the normalized reproduction output reduction rate is 1.0 or less, it means that there is a thermal demagnetization suppressing effect. The magnetic properties of the second ferromagnetic layer and the exchange coupling energy due to the non-magnetic layer are shown in Fig. 7.
Is the same as The second layer thickness t ₂ was 6 nm and 7 nm. From these results, it can be seen that the thermal demagnetization reduction effect increases as Hy increases, but has a minimum value at a certain value, and the thermal demagnetization reduction effect becomes weaker above a certain value. Further from the figure
It was found that when Hy <16 kA / m, the effect of reducing thermal demagnetization was observed, but when the value was higher than this, conversely the thermal demagnetization increased.
This tendency can be seen regardless of the film thickness. The reason is that the larger the magnetic field has the effect of promoting the magnetization reversal of the second ferromagnetic layer, but if it is too large, the magnetization tends to the radial direction. This is because the directions of the first and second magnetizations are not antiparallel, and the state becomes unstable with respect to heat. Therefore, Hy must be less than 16 kA / m. Next, the conditions of the ferromagnetic layer, which is most effective in reducing the thermal demagnetization when the antiferromagnetic layer is provided, were examined by computer simulation.
In FIG. 9, the reproduction reproduction output decrease rate obtained from FIG. 7 is taken as the vertical axis, and the horizontal axis is taken as the film thickness t ₂ of the second magnetic layer, the saturation magnetization M _s2 , and the exchange coupling energy J _ex between the ferromagnetic layers. The formula J obtained from
FIG. 3 is a diagram showing these relationships by _{obtaining ex} / (M _s2 t ₂ ). The Figure shows the results of ^{_{J ex = 0.1 × 10 -3 J}} / m 2 and ^{0. 15 × 10 -3 J / m} 2. As a result, by providing an antiferromagnetic layer, the minimum reproduction output reduction rate becomes less than 1.0 J _ex / (M _s2 t ₂ )
Range, that is, the condition of the second ferromagnetic layer for obtaining the thermal demagnetization reducing effect is

[0011]

[Equation 3] I found out. Next, based on the obtained computer simulation results, a recording medium was actually manufactured, and the magnetic characteristics and the reproduction output demagnetization rate were investigated.

FIG. 10 is a cross sectional structural view of an embodiment of an actually manufactured magnetic recording medium of the present invention.
As the substrate 13, glass having a thickness of 0.635 mm and a diameter of 65 mm whose surface was chemically strengthened was used. After cleaning this substrate, the following multilayer film was formed using a sputtering device (C-3010) manufactured by Anelva Co., Ltd. The chamber configuration of this sputtering apparatus is shown in FIG. First, Ni-37.5at% on the substrate 13
Seed layers 14 and 14 'made of Ta-10at% Zr alloy with a film thickness of 30n
The underlying layers 15 and 15 'composed of m and Pd are formed with a film thickness of 5 nm and Mn-14at% Ir.
Alloy antiferromagnetic layers 16 and 16 'with a thickness of 10 nm, Co-20a
Orientation control magnetic layers 17 and 17 'made of t% Fe alloy were formed to a film thickness of 0.2n.
m, the second magnetic layer 18 made of Co-19at% Cr-6at% Pt alloy and
18 'with a film thickness of 2 nm to 8 nm, a non-magnetic intermediate layer 19 and 19' made of Ru
With a film thickness of 0.5 nm, first magnetic layers 20 and 20 'made of a Co-18at% Cr-14at% Pt-8at% B alloy with a film thickness of 15nm, and a carbon protective layer
21 and 21 'were formed to a film thickness of 4 nm. Argon when forming each film
All (Ar) gas pressures were set to 0.9 Pa. The seed layer is formed in the chamber 22 without heating the substrate, the Pd underlayer and the antiferromagnetic layer are formed thereon in the chambers 23 and 24, the orientation control magnetic layer is formed in the ferromagnetic layer forming chamber 25, and then the heating chamber is formed. In step 26, the lamp heater is heated to 270 ° C., a second ferromagnetic layer is further formed in the ferromagnetic layer forming chamber 27, a non-magnetic intermediate layer is formed in the chamber 28, and a first magnetic layer is formed in the magnetic layer forming chamber 29. The cooling chamber 30 was cooled to about 120 ° C. in a magnetic field, and a carbon protective layer was formed in the chamber 31. Further, an organic lubricant was applied to the surface of the carbon protective layer to form a lubricating layer. A permanent magnet similar to that used for the cathode for sputtering is installed in the cooling chamber so that the magnetic field is uniformly applied in the radial direction of the disk-shaped substrate. 32
Is a load / unload chamber. First, with the thickness of the antiferromagnetic layer being 10 nm, the thickness t ₂ of the second ferromagnetic layer is set.
Was changed from 2 to 8 nm, and 7 types of samples were prepared. Next, the thickness of the second ferromagnetic layer is set to 6 nm and 7 nm, the thickness of the antiferromagnetic layer is changed from 0 to 20 nm, and a total of 6 types of samples are prepared.
The magnetic field strength applied from the antiferromagnetic layer to the second ferromagnetic layer was measured. <Comparative Example 1> For comparison, a recording medium was manufactured under the following conditions and its magnetic characteristics were examined.

Comparative Example 1 was a magnetic recording medium manufactured under the same film structure and film forming conditions as in Example 1 except that the antiferromagnetic layers 16 and 16 'were not formed. In the chamber 24, the film was not formed, but the substrate was transferred to the magnetic film forming chamber 25. Heating and cooling chamber in heating chamber 26
The cooling at 30 was set under the same conditions as in Example 1 to form the magnetic recording medium. Thickness of the second ferromagnetic layer t ₂
7 types of samples were prepared in the same manner as in Example 1.

The magnetic properties of the first ferromagnetic layer of the media described in Example 1 and Comparative Example 1 are almost the same as the values shown in Table 1. The second ferromagnetic layer is M _s2 = 0.7 T, K _u2 = 2.0 × 10 ⁵ J /
m is ^3. First, in order to investigate the effect of the antiferromagnetic layer,
A magnetic field was applied up to 800 kA / m in the circumferential direction of the film surface, and the magnetic field was changed from 800 kA / m to −800 kA / m in about 24 minutes, and the magnetization curve was measured. FIG. 12- (a) shows an example of the magnetization curve measured for the medium described in this example. In the magnetization curve, a sharp decrease in magnetization is seen when the magnetic field is returned from 800 kA / m to about 50 kA / m. This is a change corresponding to the magnetization reversal of the second ferromagnetic layer, and antiferromagnetic exchange coupling with the first ferromagnetic layer acts to cause magnetization reversal in a positive magnetic field. In the remanent magnetization state where the magnetic field is zero, the magnetization reversal of the second ferromagnetic layer is almost completed, and the magnetization directions of the first ferromagnetic layer and the second ferromagnetic layer are antiparallel to each other. Since it is important for the antiferromagnetic coupling medium that the magnetization directions of the two ferromagnetic layers are antiparallel to each other, it is important for reducing the thermal demagnetization. Magnetic field corresponding to the magnetization reversal of
The coupling magnetic field H _ex between the ferromagnetic layer and the second ferromagnetic layer was determined for each sample. Here, H _ex is defined as antiferromagnetic coupling when it has a negative value. H _ex can be obtained from the value of the magnetic field at which the curve obtained by first differentiating the magnetization curve with the magnetic field shows the first peak as shown in FIG. 12- (b). Here, the magnetic field showing the second peak is the coercive force H _cr of the medium.

FIG. 13 shows the dependence of H _ex on t ₂ . Than this,
In the conventional medium, H _ex has a positive value when t ₂ > 5 nm, whereas in this embodiment, H _ex has a negative value up to 8 nm. That is, in this example, it was found that antiferromagnetic coupling can be obtained even if t ₂ is large. Next, the magnetic field from the antiferromagnetic layer applied to the second ferromagnetic layer was examined. The sample temperature was set to 25 ° C, and the magnetic field was applied in the radial direction of the film from a maximum of 800 kA / m to −800 kA / m
After changing the magnetic field for 24 minutes, conversely, from −800 kA / m to 800
The magnetization curve was obtained by changing the magnetic field up to kA / m for 24 minutes (Fig.
14- (a)). Next, a curve obtained by first-order differentiating the magnetization curve with a magnetic field was obtained (Fig. 14- (b)). From Figure 14- (b), H _1PN = 48 kA /
When m and H _1NP = −64 kA / m, the applied magnetic field H _y = 8 kA / m from the antiferromagnetic layer can be obtained from the equation (3). Figure
15 is antiferromagnetic layer thickness dependence of H _y. From this, the antiferromagnetic layer thickness by putting about 5nm rapidly large H _{y (=} 12k
A / m), and the film thickness above that decreases, but the film thickness is 15
Above nm, it is almost constant at 7 kA / m. FIG. 16 shows the reproduction output reduction rate (standard value). From this, the effect of reducing thermal demagnetization can be obtained by setting MnIr to about 5 nm.

When the crystal orientations of the samples described in Example 1 and Comparative Example 1 were examined by an X-ray diffraction method, it was confirmed that all samples had a hexagonal close-packed structure of a ferromagnetic layer or a non-magnetic intermediate layer ( A diffraction peak corresponding to the 11.0) orientation was observed. Almost no difference was observed in the intensity of the X-ray diffraction peak between the samples, and it was confirmed that the magnetic layers of all the samples had the same good (11.0) orientation.

The composition of the Mn-Ir alloy used for the antiferromagnetic layer is Mn-
10at% Ir, Mn-12at% Ir, Mn-16at% Ir, Mn-18at% Ir, Mn-20
Similar investigations were conducted for the case of at% Ir.
Similarly, the effect of the present invention was obtained. However, H _ex increased as the Ir concentration increased. Co used for orientation control magnetic layer
The same study was performed when the composition of the -Fe alloy was Co-10at% Fe and Co-30at% Fe. When the Co-10at% Fe alloy was used, the crystal orientation of the ferromagnetic layer deteriorated. this is
It is considered that the crystal structure of the Co-Fe alloy became a face-centered cubic lattice. When a Co-20at% Fe alloy or a Co-30at% Fe alloy is used, the crystal structure of the Co-Fe alloy is considered to be a body-centered cubic lattice and is suitable for controlling the crystal orientation of the magnetic layer. Co-30a
Hex was larger in the case of using the t% Fe alloy than in the case of using the Co-20at% Fe alloy, but the tendency of the results was the same and the effect of the present invention was confirmed. Co-14at% Cr-4a in the first ferromagnetic layer
We also examined the case of using a t% Pt alloy and the case of using a Co-16at% Cr-5at% Pt-4at% B alloy, but the effect of the present invention was obtained regardless of the composition of the first ferromagnetic layer. It was confirmed that it was obtained.
Various studies were also conducted on the composition of the second ferromagnetic layer for the Co-Cr-Pt-B alloy, but it was confirmed that the effect of the present invention was obtained regardless of the composition of the second ferromagnetic layer. .

<Embodiment 2> FIG. 17 is a sectional structural view showing an embodiment of the magnetic recording medium of the present embodiment. Board 33
As the glass, a glass having a thickness of 0.635 mm and a diameter of 65 mm whose surface was chemically strengthened was used. First, a seed layer 34 and 34 'made of Ni-37.5at% Ta alloy on the substrate 33 has a film thickness of 20 nm, a base layer 35 and 35' made of Cr-20at% Ti alloy has a film thickness of 20 nm, and Cr-48at%. Mn-4a
The antiferromagnetic layers 36 and 36 'made of t% Pt alloy are formed with a thickness of 30 nm and
Second magnetic layers 37 and 37 'made of o-16at% Cr-4at% Pt alloy
A non-magnetic intermediate layer 38 and 38 'made of Ru with a film thickness of 2 nm to 8 nm, a first magnetic layer 39 and 39' made of a Co-19at% Cr-13at% Pt-8at% B alloy with a film thickness of 0.5nm. Thickness of 16 nm, and carbon protective layer 4
0 and 40 'were formed to a film thickness of 4 nm. Argon when forming each film
The (Ar) gas pressure was all 0.9 Pa. A seed layer was formed without heating the substrate, and then exposed to a slight amount of oxygen gas while being heated to 260 ° C. by a lamp heater in a heating chamber. The product of oxygen partial pressure and exposure time to the atmosphere was set to 35 mPa seconds. After forming a Cr-Ti alloy underlayer and a Cr-Mn-Pt alloy antiferromagnetic layer on it, further forming a first magnetic layer, a non-magnetic intermediate layer, and a second magnetic layer in this order, in a cooling chamber. About 1
It cooled to 20 degreeC in a magnetic field, and formed the carbon protective layer.
Further, an organic lubricant was applied to the surface of the carbon protective layer to form a lubricating layer. A permanent magnet similar to that used for the cathode for sputtering is installed in the cooling chamber,
The magnetic field is applied uniformly in the radial direction of the disk-shaped substrate. Change the film thickness t ₂ of the second magnetic layer from ₂ to 8 nm.
A variety of samples were made. Comparative Example 2 A magnetic recording medium manufactured under the same film configuration and film forming conditions as in Example 2 except that the antiferromagnetic layers 36 and 36 'were not formed was set as Comparative Example 2. The magnetic recording medium was formed under the same heating and cooling conditions as in Example 2. Seven types of samples were prepared by changing the film thickness t ₂ of the second magnetic layer in the same manner as in Example 2 above. Result of examining the t ₂ dependent H _ex, until a film thickness of 8nm Also in this embodiment similar to FIG. 14 H _ex
It was confirmed that takes a negative value. In addition, FIG. 18 shows the antiferromagnetic layer thickness dependence of the reproduction output reduction rate (standard value) in this example. From this, it was found that CrMnPt has a thermal demagnetization reduction effect with a film thickness of more than 20 nm. <Embodiment 3> FIG. 19 shows a cross-sectional structural view of a medium of Embodiment 3. The medium is an underlayer 42 on the substrate 41, then an antiferromagnetic layer 43, a third ferromagnetic layer 44, a nonmagnetic layer 45, a second ferromagnetic layer 46, and a nonmagnetic layer 4.
7, the first ferromagnetic layer 48 and the protective layer 49 are stacked in this order. The medium of this structure is different from the medium of Example 1 in that a third ferromagnetic layer 44 and a non-magnetic layer 45 are arranged between the second ferromagnetic layer 46 and the antiferromagnetic layer 43. This is intended for the third ferromagnetic layer 44 to be antiferromagnetically coupled to the second ferromagnetic layer 46 via the nonmagnetic layer 45. as a result,
The second ferromagnetic layer will receive a larger coupling magnetic field, and the antiferromagnetic coupling with the first ferromagnetic layer will also be strengthened. Therefore, by arranging the antiferromagnetic layer below the third ferromagnetic layer 44, the magnetization reversal of the third ferromagnetic layer is promoted, and the reversal mechanism causes the first and second strong layers to move. This will strengthen the antiferromagnetic coupling of the magnetic layer. <Embodiment 4> FIG. 20 shows a sectional view of the medium in Embodiment 4 of the present invention.
The medium consists of a substrate 50, an underlayer 51, then an antiferromagnetic layer 52, and a third layer.
Ferromagnetic layer 53, fourth ferromagnetic layer 54, second ferromagnetic layer 55,
The nonmagnetic layer 56, the first ferromagnetic layer 57, and the protective layer 58 are stacked in this order. The medium of this structure is different from the medium of Example 1 in that
The difference is that the third and fourth ferromagnetic layers 53 and 54 are arranged between the second ferromagnetic layer 55 and the antiferromagnetic layer 52. Here, the fourth ferromagnetic layer 54 is the third ferromagnetic layer 53 and the second ferromagnetic layer 55.
Has the purpose of weakly and ferromagnetically coupling. That is, it can be regarded as a structure in which the second ferromagnetic layer is divided by the fourth ferromagnetic layer. As a result, first, the first ferromagnetic layer and the second ferromagnetic layer exhibit antiferromagnetic coupling, and with a slight delay, the third ferromagnetic layer and the first ferromagnetic layer are antiferromagnetic. Join. That is, even if the coupling magnetic field due to the non-magnetic layer 56 is weak and the total thickness of the second and third thicknesses is large, antiferromagnetic coupling can be obtained. Therefore, by arranging the antiferromagnetic layer 52 under the third ferromagnetic layer 53, the magnetization reversal of the third ferromagnetic layer is promoted, and the time difference between the second and third magnetization reversals is increased. It is possible to shrink and strengthen more antiferromagnetic coupling. <Example 5> In Example 5, the orientation of the easy axis of magnetization of the ferromagnetic layer is inclined in the relative traveling direction of the head and the medium.
It is a medium with a structure of 4. Such a medium is excellent in R / W characteristics because the transition region of the recording magnetization is steeper than that in which the easy axis is randomly oriented in the plane, while the magnetic field required for magnetization reversal is Get bigger. Therefore, it is necessary to increase the coupling magnetic field for antiferromagnetically coupling the first, second and third ferromagnetic layers. Therefore, the magnetization reversal can be promoted by providing the antiferromagnetic layer below the second to third ferromagnetic layers.

[0019]

The magnetic recording medium of the present invention is a medium in which a ferromagnetic layer is laminated on a substrate via an underlayer, and the ferromagnetic layer has a multi-layer structure. A non-ferromagnetic layer or a ferromagnetic layer that causes weak ferromagnetic coupling is provided, and an antiferromagnetic layer is provided under the ferromagnetic layer closest to this underlayer, thereby promoting the reversal of magnetization of the ferromagnetic layer. Have a function to do. As a result, the respective ferromagnetic layers are connected by antiferromagnetic coupling or weak ferromagnetic coupling, and thermal stability is enhanced.

[Brief description of drawings]

FIG. 1 is a cross-sectional structural view showing a magnetic recording medium of the present invention and a schematic view of a magnetic moment.

FIG. 2 is a cross-sectional structure diagram showing a conventional magnetic recording medium and a schematic diagram of magnetic moment.

FIG. 3 shows the relationship between the magnetization of the conventional magnetic recording medium and the magnetic field applied to the second ferromagnetic layer.

FIG. 4 shows the relationship between the magnetization of the magnetic recording medium of the present invention and the magnetic field applied to the second ferromagnetic layer.

[FIG. 5] MH loop and first derivative curve in the radial direction of the film surface of the entire medium by computer simulation.

FIG. 6 shows an MH loop in the radial direction of the film surface of the second ferromagnetic layer by computer simulation.

FIG. 7 shows changes in reproduction output over time.

FIG. 8 shows the relationship between the magnetic field applied in the radial direction of the second ferromagnetic layer and the reproduction output reduction rate (standard value).

[Figure 9] Minimum reproduction output reduction rate (standard value) and J _ex / (M _s2 t ₂ )
connection of.

FIG. 10 is a sectional structural view showing a magnetic recording medium of Example 1.

FIG. 11 is a chamber configuration diagram of a sputtering apparatus.

FIG. 12 is a magnetization curve and a first-order differential curve of Example 1.

FIG. 13 shows the dependence of H _ex on t ₂ in Example 1.

FIG. 14 shows a magnetization curve in a radial direction of a film surface in Example 1.
First derivative curve.

FIG. 15 shows the relationship between the layer thickness of MnIr and H _y in Example 1.

FIG. 16 shows the relationship between the layer thickness of MnIr and the reproduction output reduction rate in Example 1.

FIG. 17 is a sectional structural view showing a magnetic recording medium of Example 2.

FIG. 18 shows the relationship between the layer thickness of CrMnPt and the reproduction output reduction rate in Example 2.

FIG. 19 is a sectional structural view showing a magnetic recording medium of Example 3.

FIG. 20 is a sectional structural view showing a magnetic recording medium of Example 4.

[Explanation of symbols]

1 ... Substrate, 2 ... Underlayer, 3 ... Antiferromagnetic layer, 4 ... Second ferromagnetic layer, 5 ... Nonmagnetic layer, 6 ... First ferromagnetic layer, 7 ... Protective layer, 8 ... Magnetic moment, 9 ... Magnetic moment, 10 ...
Antiferromagnetic coupling magnetic field generated in the second ferromagnetic layer by the non-ferromagnetic layer, 11, 11 '... Magnetic field applied from antiferromagnetic layer, 12- (a), (b) ... Magnetic moment, 13 ... Substrate 1
4, 14 '... Seed layer, 15, 15' ... Underlayer, 16, 1
6 '... antiferromagnetic layer, 17, 17' ... orientation control magnetic layer, 1
8, 18 '... second ferromagnetic layer, 19, 19' ... non-ferromagnetic intermediate layer, 20, 20 '... first magnetic layer, 21, 21' ... carbon protective layer, 22 ... chamber, 23 ... chamber , 24 ...
Chamber, 25 ... chamber, 26 ... heating chamber, 27 ... chamber, 28 ... chamber, 29 ... chamber, 30 ... cooling chamber, 31 ... chamber, 32 ... chamber, 33 ... substrate, 34, 34 '... seed layer, 35, 35 '... Underlayer, 3
6, 36 '... Antiferromagnetic layer, 37, 37' ... Second ferromagnetic layer, 38, 38 '... Non-ferromagnetic intermediate layer, 39, 39' ... First
Magnetic layer, 40, 40 '... carbon protective layer, 41 ... substrate, 42 ... underlayer, 43 ... antiferromagnetic layer, 44 ... third ferromagnetic layer, 45 ... non-ferromagnetic layer, 46 ... second Ferromagnetic layer, 4
7 ... Non-ferromagnetic layer, 48 ... First ferromagnetic layer, 49 ... Protective layer, 50 ... Substrate, 51 ... Underlayer, 52 ... Antiferromagnetic layer, 5
3 ... 3rd ferromagnetic layer, 54 ... 4th ferromagnetic layer, 55 ... 2nd ferromagnetic layer, 56 ... Non-ferromagnetic layer, 57 ... 1st ferromagnetic layer, 58 ... Protective layer.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshiyuki Hirayama             1-280, Higashi Koikekubo, Kokubunji, Tokyo             Central Research Laboratory, Hitachi, Ltd. F-term (reference) 5D006 BB01 BB07 BB08 CA01 CA05                       CA06 DA03 EA03 FA09                 5E049 AA04 AC05 BA06 CB02 DB12

Claims (13)

[Claims] 1. A magnetic recording medium having a ferromagnetic recording layer formed on a disk substrate via an underlayer, wherein the ferromagnetic recording layer comprises a first magnetic layer and a lower portion of the first ferromagnetic layer. And a non-ferromagnetic layer formed between the first ferromagnetic layer and the second ferromagnetic layer, and a second ferromagnetic layer formed under A magnetic recording medium comprising an antiferromagnetic layer formed as described above. 2. The magnetic recording medium according to claim 1,
The magnetic recording medium, wherein the first ferromagnetic layer and the second ferromagnetic layer are antiferromagnetically coupled via the non-ferromagnetic layer. 3. The magnetic recording medium according to claim 1,
The magnetization of the antiferromagnetic layer is oriented in the radial direction of the film surface. 4. The magnetic recording medium according to claim 1, wherein
The magnetic recording medium according to claim 1, wherein the second ferromagnetic layer is a multi-layered film in which antiferromagnetically coupled ferromagnetic films are stacked. 5. The magnetic recording medium according to claim 4,
The magnetic recording medium according to claim 1, wherein the second ferromagnetic layer is a multilayer film in which a plurality of ferromagnetic films are stacked with a non-ferromagnetic layer interposed therebetween. 6. The magnetic recording medium according to claim 1,
The second ferromagnetic layer is composed of Co, Fe, Ni or Co as a main component, and the ferromagnetic layers are laminated via a magnetic layer made of an alloy of Fe, Ni, Cr, Ta, Pt, Pd and Ru. The magnetic recording medium is a multi-layered film, wherein the ferromagnetic layers forming the multi-layered film are ferromagnetically coupled. 7. The magnetic recording medium according to claim 1,
The magnetic recording medium is formed on a disk and is obtained when a magnetic field is applied in the radial direction of the magnetic recording medium.
The MH loop is a magnetic recording medium characterized in that the curve when applied from plus to minus and the curve when applied from minus to plus are asymmetric with respect to the origin. 8. The magnetic recording medium according to claim 6,
When a negative magnetic field is applied from a positive magnetic field, a magnetic field in the second ferromagnetic layer where the magnetization of the ferromagnetic layer closest to the underlayer becomes 0 H _1PN , and a magnetic field from the negative magnetic field to a positive magnetic field _Is H _{1N P,} and H _y is the magnitude of the magnetic field applied from the antiferromagnetic layer to the ferromagnetic layer closest to the underlayer in the second ferromagnetic layer. When doing, H _y
= | H _1PN + H _1NP | / 2 is a value larger than 0, which is a magnetic recording medium. 9. The magnetic recording medium according to claim 6,
A magnetic recording medium characterized in that a magnitude H _{y of} a magnetic field applied from the antiferromagnetic layer to the second ferromagnetic layer is 0 <H _y <16 kA / m. 10. The magnetic recording medium according to claim 1, wherein the antiferromagnetic interface coupling energy density between the first ferromagnetic layer and the second ferromagnetic layer is J _ex , and the second ferromagnetic layer is the second ferromagnetic layer.
If the saturation magnetization of the ferromagnetic layer is M _s2 and the film thickness is t ₂ , then 30 kA
A magnetic recording medium characterized in that / m ≦ J _ex / (M _s2 × t ₂ ) ≦ 85 kA / m. 11. The magnetic recording medium according to claim 1, wherein the antiferromagnetic layer is CrMn, CrMnPt, MnIr, or Mn.
A magnetic recording medium comprising a material obtained by adding a non-magnetic material to Ir. 12. The magnetic recording medium according to claim 1, wherein the non-ferromagnetic layer is Ru, Ir, Rh, Cu, Re and an alloy thereof, or Ru and Nb, Ti, Pd, Pt, Au. , Cu, Pt, Pdt
A magnetic recording medium characterized by being an alloy of. 13. The magnetic recording medium according to claim 1, wherein the easy axes of magnetization of the first and second ferromagnetic layers are isotropically oriented in the medium film plane or in the circumferential direction. A magnetic recording medium characterized by being oriented in the direction of.