JP3030279B2 - Magnetic recording medium and magnetic recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium using a ferromagnetic thin film having perpendicular magnetic anisotropy as a recording layer. Related to a magnetic recording and reproducing apparatus.

[0002]

2. Description of the Related Art In recent years, there has been a remarkable increase in the amount of information, and there is a strong demand for a dramatic improvement in the storage capacity of magnetic disks, floppy disks, and magnetic tapes used as file media. In such a situation,
The magnetic recording medium is shifting from a coating type medium using fine magnetic powder to a thin film type medium using a ferromagnetic metal thin film.

[0003] In magnetic recording, information is recorded by reversing the direction of magnetization in a minute region of a ferromagnetic layer serving as a recording medium. At present, a so-called longitudinal recording method, in which the direction of magnetization is written in parallel to the medium surface, is widely used. In this recording method, the increase in recording density has been promoted by increasing the coercive force of the medium or reducing the thickness of the magnetic layer. However, the thickness is already 3 in the current longitudinal recording medium.
To be thinner than 0 nm, further thinning requires an advanced film forming technique for forming a film having tribological strength and few defects. In addition, from the viewpoint of recording / reproducing characteristics, it is difficult to avoid a decrease in reproduction output and a deterioration of a signal-to-noise ratio due to thinning. In order to prevent the signal-to-noise ratio from deteriorating due to the increase in recording density, it is necessary to reduce the size of the crystal grains constituting the recording thin film, so that the recording thin film is vulnerable to thermal disturbance, and after a long time, recorded information is lost. So-called thermal demagnetization is becoming a major problem.

On the other hand, as a method for solving the above-mentioned disadvantage, a perpendicular recording system in which recording magnetization is magnetized in a direction perpendicular to the medium film surface has been proposed. In this method, a material having strong magnetic anisotropy in the direction perpendicular to the film surface is required, and Co-C
A relatively thick alloy magnetic film having a thickness of 0.02 to 0.5 ham represented by an r-based alloy is widely used. The advantage of this recording method is that the higher the recording density, the more stable the recorded magnetization becomes in terms of energy, and is essentially suitable for high-density recording. In addition, unlike the longitudinal recording method, this method has an advantage in manufacturing that it is not necessary to reduce the film thickness or increase the coercive force in order to increase the recording density. Further, the necessity of reducing the film thickness means that the volume of the microcrystal constituting the thin film can be set to be larger than that of the longitudinal recording medium. This means that the perpendicular recording medium is easier to stabilize against thermal disturbance than the longitudinal recording medium, and the perpendicular recording method is superior as a high-density recording method from the viewpoint of heat fluctuation. ing.

The recording medium for perpendicular recording is disclosed in JP-A-57-109127, Journal of the Japan Society of Applied Magnetics, Vol. 9, No. 2, pp. 57-60 (1985), or IEEE Trans., MAG-24. No. 6, pp. 2706-2708 (1988), a Co-Cr alloy thin film is used, and non-magnetic Cr atoms Is preferably segregated. This is because the corrosion resistance is improved by creating a region with a high Cr concentration on the particle surface, and magnetic separation between particles is caused by segregation of non-magnetic Cr atoms at the grain boundaries as in the case of the longitudinal recording medium. This is because it is considered that the exchange interaction is cut off, the magnetic domain becomes finer, and the medium noise is reduced.

[0006]

However, in a combination of a ring head and a single-layer perpendicular magnetic recording medium, a medium that is always resistant to thermal fluctuations is always obtained even if manufactured under the condition that segregation of Cr atoms progresses. Rather, it was not until the benefits of perpendicular recording were brought out. An object of the present invention is to solve the above-described problem of perpendicular magnetic recording and to provide a magnetic recording medium having stable characteristics against thermal fluctuations and a magnetic recording / reproducing apparatus using the same.

[0007]

The inventors of the present invention have conducted intensive studies on the relationship between magnetic recording / reproducing characteristics and medium characteristics. As a result, the stability against thermal fluctuation is closely related to the magnetic characteristics of the outermost surface region of the recording layer. And reached the present invention. That is, in the perpendicular magnetization film of a Co—Cr alloy widely used in perpendicular recording, the magnetic anisotropy in the outermost surface layer is smaller than the inside of the film. As a result, the reverse magnetic domain propagates to the inside of the film. Therefore, the strength of the magnetic field generated by the reverse magnetic domain is reduced, and the structure becomes thermally unstable. To prevent this, it is effective to provide a thin film having strong perpendicular magnetic anisotropy on the surface of the recording film. However, for that purpose, a material having a much larger anisotropy constant than a Co—Cr alloy is required, and such a material is limited to a very small number of materials such as a Co—Pt alloy.

[0008] In the present invention, it has the property of easy perpendicular magnetization.
10 nm or less on both sides or one side of magnetic recording film
Sm-Co based magnetic film or Fe-Nd-B based magnetic film
The above object is achieved by forming . As the magnetic film having the in-plane easy magnetization characteristic, an Sm-Co-based magnetic film or an Fe-Nd-B-based magnetic film which has a large anisotropy constant and is hardly affected by thermal fluctuation is particularly suitable.

Accordingly, the present invention is, S with the recording medium used in the perpendicular magnetic recording, the in-plane easy magnetization characteristic on both surfaces or one surface of the magnetic recording film having a perpendicular easy magnetization characteristic
An m-Co-based magnetic film or an Fe-Nd-B-based magnetic film is formed. Sm with easy in-plane magnetization characteristics
The -Co magnetic film or the Fe-Nd-B magnetic film preferably has a thickness of 10 nm or less, more preferably approximately 1 nm. This is because if the film thickness is too large, the in-plane recorded component becomes large and the advantage of perpendicular recording is lost.

[0010] Sm-Co based magnetism having easy in-plane magnetization characteristics
The film or the Fe-Nd-B-based magnetic film has a coercive force of 100 Oe or more, more preferably 50 Oe, when measured in the in-plane direction.
It is preferably at least 0 Oe. If the coercive force is less than 100 Oe, domain walls are likely to be formed in the in-plane magnetized film, which causes noise. As a magnetic film with easy in-plane magnetization characteristics,
Sm-Co based magnetic films or Fe-Nd-B based magnetic films are preferred. In the Sm-Co based magnetic film, Sm is 1
A high coercive force can be obtained with a composition of 5 to 22 at%, preferably 18 to 20 at%. In the Fe—Nd—B based magnetic film, Nd is 10 to 35 at% and B is 5 to 20 at%.
Is more preferable, and the more preferable composition range is Nd of 10 to 15 at% and B of 5 to 10 at%.

The present invention is also directed to a magnetic recording medium, a driving unit for driving the magnetic recording medium to rotate, a magnetic head for recording and reproducing, a means for moving the magnetic head relative to the magnetic recording medium, A magnetic recording / reproducing apparatus including means for reproducing an output signal from a head, wherein the magnetic recording medium according to the present invention is used as a magnetic recording medium.

According to the present invention, Co-C for perpendicular magnetic recording
Ultra-thin in-plane easy magnetization film on r-type thin film medium
Sm-Co based magnetic film or Fe-Nd-B based magnetic film
By providing the conductive film , stability against thermal fluctuation is improved. Further, as a secondary effect, a high reproduction output and a low medium noise characteristic are obtained, and the signal-to-noise ratio (S / N) is also improved. Further, the magnetic recording / reproducing apparatus using the perpendicular magnetic recording medium according to the present invention has a high reproduction output, an S / N ratio, and excellent recording retention life characteristics.

[0013]

Embodiments of the present invention will be described below. <Embodiment 1> A 30-nm-thick Ti— film is formed on a disk substrate made of an Al—Mg alloy, on which a nickel (Ni) and phosphorus (P) alloy plating film is applied, by a sputtering method.
After forming a 10 at% Cr alloy film, Co-35 at%
Non-magnetic Co-Cr of 0.02 ham thickness with Cr composition
An underlayer made of an alloy thin film was formed at a substrate temperature of 200 ° C. Thereafter, a Co-19 at% Cr-1 having a thickness of 30 nm was used.
A quaternary alloy of 0% Pt-2% Ta was formed as the magnetic recording layer. Further, a magnetic film having a composition of Co-18 at% Sm was formed to a thickness of 2 nm at a substrate temperature of 300 ° C. for the purpose of suppressing generation of reverse magnetic domains in the surface layer. Finally, a carbon film having a thickness of 15 nm was formed as a protective film. A sample manufactured by such a method is referred to as a disk S1.

A disk S2 was made of the same structure as the disk S1 except that the thickness of the Co—Sm alloy film was changed to 1 nm. Further, for comparison, a sample having the same structure as that of the disk S1 was prepared under the same conditions except that a Co-Sm thin film was not formed, and was used as a disk R1. Disks S1, S2, R1 manufactured by the above method
Co-19at% Cr-10at% Pt-2at% T
a The magnetic recording layer has a hexagonal crystal structure.
It was confirmed by an X-ray diffractometer that the c-axis was oriented in a direction perpendicular to the film surface. The magnetic properties of the sample thus manufactured were measured with a vibrating sample magnetometer (VSM) to determine the saturation magnetization (Ms) and the coercive force (Hc).
The magnetic field was applied in a direction perpendicular to the film surface. The results are shown in the magnetization curve of FIG. 1 and collectively shown in Table 1 below.

As is apparent from FIG. 1, as the magnetic field strength of the disk S1 decreases, a gradual decrease in magnetization is observed due to the demagnetization of the in-plane magnetization curve of the surface. This tendency does not change at a strength of 400 Oe. Further, when the reverse magnetic field intensity is 400 Oe or more, the magnetization curve has a shoulder, and when the reverse magnetic field intensity is more than 400 Oe, irreversible magnetization reversal occurs and the magnetization starts to decrease rapidly. That is, in the disk S1, it is shown that a reverse magnetic domain is generated in the perpendicular magnetization film near 400 Oe.

On the other hand, in the disk R1, the shoulder of the magnetization curve is in the first quadrant and the fourth quadrant, and irreversible magnetization reversal has already started just before the direction of the magnetic field is reversed. Thus, the disc S1 according to the present invention and the disc R1 for comparison are used.
There is a great difference in the magnitude of the magnetic field at the shoulder position in the magnetization curve. The thickness of the Co-Sm film is 1
The magnetization curve of the disk S2 of nm has almost the same shape as that of S1, and it can be confirmed that the same effect appears even when the thickness of the Co-Sm film is as thin as 1 nm. Since the film provided to suppress the generation of the reverse magnetic domain is an in-plane magnetization easy film, there is a possibility that some trouble may be caused when perpendicular recording is performed. Therefore, it is desirable to make the thickness of the film provided on the surface as small as possible.

Next, these disks S1, S2, R1
Were evaluated using a magnetic disk recording / reproducing tester. The magnetic head used for recording and reproduction is a thin film head having a gap length of 0.2 μm, a track width of 4.5 μm, and a coil turn of 30 turns. The distance between the medium facing surface of the head and the medium surface, the flying height is 0.04 Ham, and the peripheral speed is 10 m.
/ S, and under the condition of a linear recording density of 200 kFCI, the reproduction output and the medium noise when the “all 1” signal was recorded were measured. Further, after recording at 200 kFCI, the recording medium was left as it was, and the change with time of the reproduction output was examined. The results are shown in Table 1.

As is apparent from Table 1, when the reproduced output of the disks S1 and S2 according to the present embodiment after 100 hours is compared with the comparative disk R1, the output of the disk R1 is 8
%, Whereas the discs S1 and S2 showed almost no decrease in output of 0.5% and 0.8%, respectively. Further, the discs S1 and S2 are superior to the comparative disc R1 in both the reproduction output and the medium noise, and it can be seen that the discs S1 and S2 are also effective in improving the recording and reproduction characteristics.

The above results indicate that the magnetic field causing irreversible magnetization reversal, that is, the position of the shoulder of the magnetization curve is opposite to the direction of the magnetic field applied first, and the larger the absolute value is, the more the magnetic recording medium can be used. This indicates that the recording / reproducing characteristics are excellent and that the recording medium is stable against thermal fluctuation. The reason why such magnetic characteristics were obtained in the disks S1 and S2 is that a magnetic film was formed on the surface of the magnetic recording film such that the anisotropic magnetic field was large and the direction of easy magnetization was in-plane. Even if the film is very thin, having a thickness of 1 nm or 2 nm, it has a great effect in suppressing the generation of nucleation sites that cause irreversible magnetization reversal on the film surface, that is, reverse magnetic domains. Presumed. It is considered that the reverse magnetic domain is a main cause of the medium noise, and the medium noise is also reduced because the reverse magnetic domain hardly occurs. Similarly, it is considered that the fact that the reverse magnetic domain is unlikely to be generated has a good effect in improving the thermal stability.

In this embodiment, Co-Sm
Since the thickness of the film was as thin as 1 to 2 nm, the crystal structure and in-plane coercive force of the Co-Sm film could not be identified. In order to examine the crystal structure and magnetic properties, the underlayer Co-35 was used.
An at% Cr layer is formed by a sputtering method and has a thickness of 30%.
A Co-Sm film of nm was produced. As a result, it was confirmed from the measurement of the magnetic characteristics that the crystal structure was amorphous and that the film was an in-plane magnetization easy film having an in-plane coercive force of about 800 Oe.

<Embodiment 2> Next, an example in which an Fe-Nb-B-based magnetic thin film is formed on the surface of a perpendicular magnetic recording film will be described. The method of preparing the sample is the same as that in Embodiment 1, but in this embodiment, Co-19 at% Cr-
After forming a quaternary alloy of 10 at% Pt-2 at% Ta as a recording layer, Fe-12 at% Nd was used as a surface magnetic film.
A magnetic film having a composition of −8 at% B and a thickness of 2 nm was formed at a substrate temperature of 350 ° C. Thereafter, a carbon protective film having a thickness of 15 nm was formed to obtain a disk S3.

The magnetic characteristics and recording / reproducing characteristics of the disk S3 are summarized in Table 1 below. As can be seen from Table 1, the value of the nucleation magnetic field is negative in the disk S3, and reverse magnetic domains are less likely to be generated than in the comparative disk S3. As a result, both the recording / reproducing characteristics and the stability against thermal fluctuation have been improved. These effects are not as great as those of the disks S1 and S2, but show that the Fe-Nb-B-based magnetic film has the same effect as the Sm-Co-based magnetic film. Also in this sample, Fe-Nb
In order to examine the crystal structure and magnetic properties of the B film, a 30 nm thick Fe-12 at% Nb-8 at% was directly formed on the underlayer.
A B film was produced. As a result, it was confirmed that the Fe—Nb—B film was an in-plane magnetization easy film having an amorphous crystal structure and an in-plane coercive force of 300 Oe.

<Embodiment 3> Back surface of perpendicular magnetic recording film,
That is, an example in which a magnetic thin film having in-plane easy magnetization characteristics is formed on the substrate side will be described. The method of preparing the sample is almost the same as that in Embodiment 1, but in this embodiment, C
After forming a non-magnetic Co-Cr film of o-35 at% Cr, a Co-18 at% Sm in-plane magnetized film is formed at a substrate temperature of 30.
It was formed to a thickness of 2 nm at 0 ° C. After a while, thickness 30n
m Co-19 at% Cr-10 at% Pt-2 at%
A perpendicular magnetization film of Ta was formed as a magnetic recording layer, and a carbon film having a thickness of 15 nm was formed thereon as a protective film. That is, in the present embodiment, the in-plane magnetization film is formed on the back surface of the magnetic layer.

Using the sample prepared in this manner as a disk S4, the magnetization curve and the recording / reproducing characteristics were measured in the same manner as in the first embodiment. The results are shown in Table 1. As is evident from Table 1, the nucleation magnetic field of the disk S4 is-as in the case of the disks S1 and S2.
It shows a large value of 415 Oe, which indicates that a reverse magnetic domain is hardly generated. It was also found that the recording / reproducing characteristics and the output decrease after 100 hours were superior to the comparative disk R1.

<Embodiment 4> A sample was prepared in which an in-plane magnetized film was formed on the front and back surfaces of a perpendicular recording film. The manufacturing method of the sample of the present embodiment is a combination of the first and third embodiments. The in-plane magnetized film made of Co-18 at% Sm having a thickness of 2 nm is made of Co-19 at% Cr-10 at% Pt. −
The film configuration is such that the rear surface and the front surface of the perpendicular magnetization film of 2 at% Ta are formed. Using this sample as a disk 5, the magnetic characteristics and the recording / reproducing characteristics were measured in the same manner as in the first embodiment. Table 1 shows the results. As is clear from Table 1, the provision of the in-plane magnetic film on both the front and back surfaces of the perpendicular magnetic film results in a nucleation magnetic field of -520 Oe, which is larger than the case where the in-plane magnetic film is provided only on one side, and the recording / reproducing characteristics It was also found that the output reduction after 100 hours was further improved.

[0026]

[Table 1] * The sign indicates that the direction of the applied magnetic field was positive. Here, the nucleation magnetic field is the magnitude of the magnetic field at which the magnetization curve starts irreversible magnetization reversal, that is, the magnetic field at the shoulder of the magnetization curve. ** The value of the comparison magnetic disk R1 was set to 0 dB.

<Embodiment 5> FIG. 2 is a schematic view showing an example of a magnetic disk drive according to the present invention. Head disk
A plurality of magnetic disks 1 are mounted on a spindle shaft in an assembly 4 and a medium drive system (motor) 5
Is rotated at high speed. As the magnetic disk 1, the disk manufactured in the above embodiment is used.
A magnetic head 2 for recording / reproducing a signal on / from a magnetic recording surface of the disk is arranged, and one of the magnetic heads 2 functions as a servo head. The magnetic head 2 is moved in a substantially radial direction of the magnetic disk 1 by the head drive system 6 via the actuator 3. The apparatus further includes a recording / reproducing system 7 for recording / reproducing data, a signal processing system 8 for processing the signals, a control system 9 for controlling these and the driving system, and exchange of data with a host device. Device I / F to perform
The unit 10 and the like are provided.

When reading was performed using the magnetic disk device manufactured in the above-described embodiment using this magnetic disk device, a sufficiently high reproduction output and low medium noise could be obtained in each case. After recording information, 100
Even if it is left for more than an hour, there is almost no decrease in playback output,
The thermal stability was also found to be excellent.

[0029]

According to the present invention, the thermal stability of a magnetic recording medium can be improved, and the retention life of recorded information can be improved. Further, the reproduction output is improved and the medium noise is reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing magnetization curves of a sample according to the present invention and a comparative sample in which an in-plane magnetization easy film is provided on the surface.

FIG. 2 is a schematic diagram illustrating an example of a magnetic recording / reproducing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Magnetic disk 2 ... Magnetic head 2 3 ... Actuator 4 ... Head disk assembly 5 ... Medium drive system 6 ... Head drive system 7 ... Recording / reproducing system 8 ... Signal processing system 9 ... Control system 10 ... Device I / F part

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiyuki Hirayama 1-280 Higashi Koigabo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (56) References JP-A-10-334443 (JP, A) JP-A-60 -261026 (JP, A) JP-A-63-56812 (JP, A) JP-A-1-125715 (JP, A) JP-A-7-176027 (JP, A) (58) Fields investigated (Int. . ^7, DB name) G11B 5/66

Claims (2)

(57) [Claims] In a recording medium used for perpendicular magnetic recording, an Sm-Co-based magnetic film having a thickness of 10 nm or less is formed on both surfaces or one surface of a magnetic recording film having easy perpendicular magnetization characteristics.
Is a magnetic recording medium formed with an Fe-Nd-B-based magnetic film . 2. A magnetic recording medium, a drive unit for driving the magnetic recording medium to rotate, a magnetic head for recording and reproduction, a means for moving the magnetic head relative to the magnetic recording medium, and the magnetic head A magnetic recording / reproducing apparatus comprising: means for reproducing an output signal from the apparatus; wherein the magnetic recording medium according to claim 1 is used as the magnetic recording medium.