JP2000298892A - Multiple-value recording medium and multiple-value magnetic recording data reproduction system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multiple-value magnetic recording medium that is capable of multiple-value recording where magnetization information and form change information are combined by utilizing expansion and contraction depending on the magnetization direction of a magnetic body and further a multiple-value magnetic recording data reproduction system for reading multiple-value data in a contact reproduction system from the multiple-value recording medium. SOLUTION: A thin-film magnetic material where volume changes depending on a magnetization direction is used as a recording layer, and a multiple-value magnetic recording medium for taking a four-value state due to a magnetization arrangement where magnetization is in up/down directions vertical to a film surface or left/right directions horizontal to the direction of the film surface is manufactured. Also, a magnetic resistance-(MR)-type magnetic head is used, a signal by magnetic flux and a thermal asperity signal being generated when hitting against a projection being generated by form change by the magnetic head are simultaneously detected for separating magnetic information/volume information by signal processing. The recording multiple-value data are reproduced by the combination of each separated information.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multivalued magnetic recording system for realizing high-density magnetic recording and a medium therefor.

[0002]

2. Description of the Related Art In recent years, magnetic disk drives have become increasingly denser.
Large capacity is realized by various technologies. These techniques include, for example, lower magnetic spacing, finer crystal grains of a magnetic disk medium material, and the like. As the research and development of these technologies have progressed, the recording density per unit area of a hard disk has been significantly improved.

[0003]

However, a recording bit on a magnetic disk has a minimum stable size determined by the strength of anisotropy and thermal energy. Therefore, it is considered that there is a limit to a method of simply reducing the recording bit size. In order to overcome this and realize higher density recording, it is necessary to study the recording method itself.

In order to achieve higher-density recording under the condition that such a minimum stable size exists, it is effective to realize multi-level recording in which one recording unit has more information. However, in the conventional magnetic recording method, only binary recording has been adopted. For example, in a longitudinal magnetic recording method in which a magnetic field is applied in a direction parallel to the film surface of a magnetic disk,
Binary recording is realized by utilizing the fact that the direction of magnetization alternates between the forward direction and the reverse direction. Also, in a perpendicular magnetic recording method in which a magnetic field is applied in a direction perpendicular to the film surface of a magnetic disk, binary recording is realized by utilizing the fact that the direction of magnetization alternates between a forward direction and a reverse direction. . As described above, conventionally, multi-level recording has not been realized.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a multilevel magnetic recording medium in which one recording bit has three or more levels of multilevel information. More specifically, there is provided a magnetic disk medium in which one recording bit has three or more values of multi-value information by utilizing a change in form of the recording bit due to the generation of magnetism in addition to the magnetization direction of the recording bit. That is.

Another object of the present invention is to provide a multi-valued magnetic recording data reproducing system for reproducing recorded data from the multi-valued magnetic recording medium.

[0007]

According to a first aspect of the present invention, there is provided a multi-valued magnetic recording medium, comprising: a recording layer for recording data; Is a magnetic material whose volume expands and contracts due to the
It is made of a magnetic material whose shrinking direction is determined, and uses a combination of a change in form of the magnetic material and a magnetization direction of the magnetic material as a recording state. Therefore,
Since the recording state is obtained by combining the morphological change and the magnetization direction, multi-value recording exceeding two values is possible.

According to a second aspect of the present invention, in the multi-valued magnetic recording medium, the magnetic material is processed into a columnar shape to form a columnar protrusion, and the plurality of columnar protrusions are arranged on the substrate. Have a recording state by a combination of a change in shape and a change in magnetization direction when a magnetic field is applied. According to such a configuration, the shape of each of the cylindrical projections can be changed independently, so that the form change can be efficiently caused. In other words, high controllability can be imparted to the form change.

According to a third aspect of the present invention, in the multi-valued magnetic recording medium, a plurality of cylindrical holes having a predetermined diameter are formed in a substrate made of a non-magnetic material, and the recording material is formed by embedding the magnetic material in these holes. There is a configuration that allows. According to such a configuration, the columnar protrusion can be efficiently formed, and the mechanical resistance against the collision of the magnetic head can be improved.

According to a fourth aspect of the present invention, in the multilevel magnetic recording medium, the substrate is made of non-magnetic ceramics. When the columnar projections are embedded in the nonmagnetic ceramics, the columnar projections can be mechanically protected without magnetically affecting the columnar projections.

According to a fifth aspect of the present invention, the diameter of the hole is approximately 0.1 micron.
With such a size, the recording bits can be made sufficiently small, and high-density magnetic recording can be achieved.

7. The multi-valued magnetic recording medium according to claim 6, further comprising a substrate having a plurality of projections formed on a surface thereof, wherein the magnetic material is provided on a surface of the substrate on which the projections are formed, and wherein the recording layer is provided. Is the configuration. According to such a configuration, the recording layer is divided by the protrusion, and the total recording between the protrusions constitutes the recording bit. As a result, the morphological change can be performed more efficiently, as in the case where the magnetic material is formed in the cylindrical shape.

According to a seventh aspect of the present invention, the substrate is made of InP, and the projection is made of InAs. According to such a configuration, pyramid-shaped (quadrangular pyramid-shaped) projections can be naturally formed as described later,
Protrusions can be efficiently formed.

In the multilevel magnetic recording medium according to the present invention, the substrate is made of plastic, and the projections are also made of plastic. Because it is made of plastic, I
As compared with the case where the substrate is made of nP, the material can be easily obtained and the manufacturing equipment can be simplified.

According to a ninth aspect of the present invention, in the multi-valued magnetic recording medium, the protrusion is formed in a quadrangular pyramid shape having a size of several nm. According to such a configuration, the protrusion can be easily configured.

A multi-valued magnetic recording medium according to a tenth aspect is configured such that an Fe-Rh alloy is used as the magnetic material. According to this Fe-Rh alloy, the morphological change due to the application of a magnetic field can be increased.

The multi-valued magnetic recording medium according to claim 11 is configured such that the magnetic material uses a magnetic shape memory alloy. With such a configuration as well, the morphological change due to the application of the magnetic field can be increased.

A multi-valued magnetic recording medium according to a twelfth aspect has a configuration using Mn-Ga as the magnetic shape memory alloy. In particular, according to the Mn-Ga alloy, the morphological change due to the application of a magnetic field can be further increased.

A multi-valued magnetic recording data reproducing system according to claim 13, wherein a magnetization direction detecting means for detecting a magnetization direction of each recording bit in a recording layer of the multi-valued magnetic recording medium, and said each recording in the recording layer. And a morphological change detecting means for detecting a morphological change of a bit, wherein the detection of the magnetization direction and the detection of the morphological change are performed simultaneously for the same recording bit. At the same time, since the magnetization direction and the morphological change are detected, a combination of the magnetization direction and the morphological change of a predetermined recording bit can be reliably detected.

According to another aspect of the present invention, the form change detecting means detects the form change via a thermal asperity signal, and the magnetization direction detecting means magnetically records the magnetization direction. The configuration is such that detection is performed via a change in magnetic flux of a signal. According to such a configuration, a form change can be indirectly detected by the thermal asperity signal.

According to a fifteenth aspect of the present invention, in the multi-valued magnetic recording data reproducing system, the shape change detecting means and the magnetization direction detecting means are MR magnetic heads. MR
If a magnetic head is used, a magnetic signal and a thermal asperity signal can be detected simultaneously, so that the magnetization direction and the morphological change can be easily detected simultaneously.

A multi-valued magnetic recording data reproducing system according to claim 16 is configured such that the MR magnetic head performs contact reproduction on the multi-valued magnetic recording medium. According to such a configuration, the thermal asperity signal and the magnetic signal can be simultaneously detected by contact reproduction.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. First, the principle of the present embodiment will be described. Magnetic materials that undergo a morphological change when a magnetic field is applied are known. In the present embodiment, a thin-film magnetic material whose morphological change is large among the materials whose morphological change depends on the magnetization direction is employed as the recording layer.

And a vertical direction whose magnetization direction is perpendicular to the film surface, or a horizontal direction whose magnetization direction is horizontal to the film surface direction.
The quaternary state can be formed in one magnetic bit by taking any of the directions. In other words, a quaternary state based on these magnetization arrangements can be formed on the recording bit.

In the embodiment described below, a magnetoresistive (MR) type magnetic head is used to simultaneously detect a signal due to magnetic flux and a thermal asperity signal generated when the magnetic head collides with a projection. The signal due to the magnetic flux and the thermal asperity signal are obtained by being superimposed. By subjecting this signal to predetermined signal processing, magnetic information and volume information can be separated. As a result, the above-described multi-value information can be reproduced.

In this embodiment, the magnetic head generates heat by colliding with the recording medium, and utilizes a thermal asperity signal which appears at that time. Therefore, any magnetic head in which such a phenomenon occurs can be used. However, since the thermal asperity effect is actually remarkable in the MR head, this embodiment will describe a case where data is reproduced by the MR head.

Incidentally, the magnetic recording system conventionally used is a binary recording system using two kinds of magnetization directions as two kinds of recording states. In magnetic recording, when the recording bit is made smaller, the volume of the magnetized portion decreases. It is known that the recording bit becomes superparamagnetic as the volume decreases, and the recording magnetization state becomes unstable due to thermal fluctuation.

For this reason, the output of the reproduced signal decreases with the passage of time, and eventually becomes small to such an extent that the signal cannot be restored even if the signal processing is performed. Based on the influence of this thermal fluctuation, it is expected that there is a limit in the recording density of magnetic recording.

Although the limit due to the influence of the thermal fluctuation changes depending on the magnitude of the magnetic anisotropy of the magnetic material, it is considered that the limit inherently exists in any magnetic material. I have. Therefore, it is considered that the limit due to the influence of the thermal fluctuation is one of the factors defining the limit of the physical recording density.

In order to overcome the limitation of the recording density of the magnetic recording and to further improve the recording density, it is necessary to use one of the following methods.
It is necessary to include a large amount of information in one recording bit.

Incidentally, it is generally known that a magnetic material (magnetic material) undergoes a morphological change when its magnetization direction is aligned. This phenomenon is manifested in order to eliminate the increase in magnetic energy when the directions of the magnetic moments are aligned by distorting the crystal lattice.

For many magnetic materials, the morphological change rate is 10 ^-6.
Less than and very small. Therefore, although research on physical properties related to the morphological change is being advanced, almost no magnetic recording system that positively uses the morphological change for magnetic recording is known. This means that a magnetic recording medium and a magnetic recording system that positively utilize the morphological change for magnetic recording are also hardly known.

In the conventional magnetic recording method, as described above, only the difference in the direction of magnetization, that is, the difference in the distribution of magnetic flux is detected. However, a so-called contact state in which the magnetic head and the magnetic disk medium are in contact with each other has appeared in the recording / reproducing operation as the spacing has been reduced. In such a so-called contact recording / reproducing operation, a recording film (magnetic recording film) depending on the direction of magnetization is provided.
Changes appear as irregularities in the surface morphology, and affect the reproduced signal. Specifically, the unevenness of the surface form has appeared as noise in the reproduced signal.

The reason for this is that irregularities of the surface morphology, that is, morphological changes are generally randomly distributed, and it is generally considered that they cannot be handled as recorded information. For this reason, it has been recognized that reducing unevenness of the surface morphology is an important issue for good recording and reproduction of information.

More specifically, when a magnetic head collides with a disk surface in detecting a magnetic flux when reproducing information, a change in current caused by a rise in temperature and cooling at a detection portion (magnetic head) of the magnetic head causes a change in a reproduced signal. It overlaps and appears as a disturbance called so-called thermal asperity in the reproduced signal. At the time of filing the present invention, improvements in the head-disk interface and development of signal processing to reduce this have been made widely.

However, if a signal which has been conventionally treated as disturbance or noise is recognized as a periodic signal accompanying recording bits, such a change in form of the magnetic recording material can be regarded as information recording. Is possible. If a morphological change due to a change in the magnetization direction is reversibly generated at a position associated with the magnetic recording bit, multi-level recording combining the magnetic change and the morphological change can be realized. This is the basic principle of the present invention.

Now, the specific position as described above (ie,
In order to realize the morphological change in the recording bit),
First, it is necessary to use a ferromagnetic material having a large structural distortion generated in a direction depending on the magnetization direction as a magnetic recording material. Examples of such a material include an Fe-Rh alloy and a Mn-Ga alloy having a large coupling constant between magnetism and lattice.

However, even when such a magnetic recording material is used, when a thin film having a random orientation is formed, a change in volume due to the magnetization direction is dispersed, and a large morphological change cannot be obtained as a whole.

On the other hand, when a thin film is preferentially oriented in a direction in which the coupling constant between the magnetism and the lattice is large, if the magnetic recording film is magnetized in the direction perpendicular to the film surface, the volume increases in the film thickness direction. When magnetized in the in-plane direction, a state in which the volume does not change is realized. It should be noted that the fact that the volume does not change means that the volume shrinks in the film thickness direction.

When contact recording / reproduction is performed on the magnetic recording film formed in such a state that the magnetic and lattice coupling constants are preferentially oriented in a direction having a large coupling constant, the quaternary multi-value recording is performed as follows. realizable. First, if a perpendicular magnetic recording state in which magnetization is applied vertically is used, the volume of recording bits increases, so that binary recording superimposed on the thermal asperity signal can be realized. In this case, the directions of magnetization corresponding to the two values are upward and downward.

Further, if the in-plane magnetic recording state in which magnetization is applied in a direction parallel to the film surface is used, the volume does not change, so that binary recording without a thermal asperity signal can be realized. Therefore, considering the presence or absence of the thermal asperity signal, four states can be taken, and multi-value recording of a total of four values is possible as described above.

Hereinafter, various embodiments based on such a principle will be described in order. [First Embodiment] FIG. 1 is an explanatory diagram showing a configuration of a magnetic disk according to a preferred first embodiment of the present invention. A crystal orientation control layer 2 of Cr or the like on a substrate 1 made of glass or the like.
, A Fe-Rh magnetic / morphological recording layer 3, a protective layer 4 made of a C-based thin film, and a lubricating layer 5 are sequentially laminated. Here, the thickness of the crystal orientation control layer 2 of Cr or the like is 20 nm,
The thickness of the e-Rh magnetic / morphological recording layer 3 is 100 nm, the thickness of the protective layer 4 made of a C-based thin film is 5 nm, and the thickness of the lubricating layer 5 is 2 nm.

Each layer other than the lubrication layer 5 is produced by a direct current or high frequency sputtering method. The lubrication layer 5 is formed by a spin coating method or the like. Note that the Fe-Rh magnetic / morphological recording layer 3 is manufactured by orienting the crystal in the (110) direction in which the magnetic / lattice coupling constant is maximum.

Along the tracks of the magnetic disk (recording medium) thus manufactured, along the film surface direction (longitudinal direction)
And magnetization was alternately applied in a direction perpendicular to the film surface. Then, the magnetic head was brought into contact with the magnetic disk (recording medium), and the recorded data was contact-reproduced. An explanatory diagram showing a graph of the reproduced signal in this case is shown in FIG.

In FIG. 2, the horizontal axis represents the position in the track direction, and the vertical axis represents the signal intensity. In this figure, a broken line represents a thermal asperity signal, and a solid line represents a magnetic flux signal, that is, a reproduced signal by ordinary magnetic recording. Arrows in the vertical direction in the drawing indicate that the direction of magnetization is perpendicular to the film surface, and arrows in the horizontal direction indicate that the direction of magnetization is parallel to the film surface. .

In the state magnetized in the longitudinal direction, a waveform corresponding to the longitudinal signal is observed, whereas when magnetized in the vertical direction, a waveform in which the thermal asperity signal is superimposed on the magnetic reproduction signal is observed. . Therefore, by detecting the rise of the thermal asperity signal, it can be determined that the recording state is in the vertical direction. That is, when a thermal asperity signal is detected, it can be determined that the magnetic reproduction signal is a signal based on perpendicular magnetization.

As described above, by combining the recording state by the perpendicular magnetization and the longitudinal recording state, quaternary recording can be performed on one recording bit. As described above, multi-level recording can be realized by a system using the contact reproduction method.

[Second Embodiment] An example in which the material of the magnetic / morphological recording layer of the magnetic disk (recording medium) having the structure described in the first embodiment is changed to an Mn-Ga alloy.

In the second embodiment, a Cr crystal orientation control layer 2 / Mn—Ga magnetic / morphological recording layer 3a / C-based protective layer 4 / lubricating layer 5 are sequentially laminated on the surface of a glass substrate 1 to form a magnetic disk. A medium was prepared. Here, the thickness of the Cr crystal orientation control layer 2 is 20 nm, the thickness of the Mn-Ga magnetic / morphological recording layer 3a is 100 nm, and the thickness of the C-based protective layer 4 is 5 nm.

The magnetic recording / reproducing characteristics of the magnetic disk manufactured in this manner were measured using the contact recording / reproducing method as in the first embodiment. Note that Mn-Ga
The alloy was prepared so as to have a (111) orientation.

FIG. 3 is an explanatory diagram of a graph of the reproduced signal in this case. In FIG. 3, as in FIG. 2, the horizontal axis represents the position in the track direction, and the vertical axis represents the signal intensity. In this figure, a broken line represents a thermal asperity signal, and a solid line represents a magnetic flux signal, that is, a reproduced signal by ordinary magnetic recording. Arrows in the vertical direction in the drawing indicate that the direction of magnetization is perpendicular to the film surface, and arrows in the horizontal direction indicate that the direction of magnetization is parallel to the film surface. .

As shown in this figure, Mn-Ga
When the alloy thin film is used as the magnetic / morphological recording layer 3,
In the longitudinal recording, only a magnetic reproduction signal was detected, and in the perpendicular recording, a signal in which a thermal asperity signal was superimposed on the magnetic reproduction signal was detected. Therefore, in the second embodiment, quaternary printing can be realized as in the first embodiment.

[Third Embodiment] In the magnetic disk (recording medium) shown in the first and second embodiments, when the size of the recording bit is reduced to about 0.5 μm, the magnetic recording in the vertical direction can be performed. It was confirmed by experiments of the present inventors that it became difficult to discriminate longitudinal magnetic recording.

According to the experiment of the present inventor, even if magnetization is applied to a recording bit having a size of about 0.5 μm in a direction perpendicular to the film surface, stress is generated by a film around the recording bit. The unevenness of the recording state caused by the perpendicular magnetization is 0.
It was less than 2 nm. As a result, the thermal asperity signal was reduced, and it became difficult to discriminate perpendicular recording from longitudinal recording.

In order to avoid such a phenomenon, in the third embodiment, the (110) -oriented Fe-Rh alloy is processed and formed into a column shape. This is called a cylindrical bit. Then, a large number of the cylindrical bits were arranged on the surface of the magnetic disk such that the longitudinal direction was perpendicular to the film surface of the magnetic disk. Each cylindrical bit has a diameter of 0.1 micron and a height of 100 nm.

The cylindrical bit is manufactured as follows. First, a crystal orientation control layer 2, a magnetization / morphological recording layer 3, and a C-based protective layer 4 are sequentially formed on a substrate 1 by sputtering. Next, a photoresist is applied on the protective layer 4, and then a fine mask pattern is formed on the photoresist by electron beam exposure. Then, portions other than the columnar bits are cut by ion milling. As described above, a columnar bit as shown in FIG. 4 can be formed on the substrate 1.

FIG. 4 is an explanatory diagram showing the shape of the magnetic disk according to the third embodiment. The thickness of each layer on the substrate 1 of the magnetic disk is 5
0 nm, the magnetization / morphological recording layer is 100 nm,
The thickness of the C-based protective layer 5 is 5 nm.

As a method of forming a columnar bit, a similar shape can be obtained by a wet method using a method of dipping in dilute hydrochloric acid. However, in the experiments of the present inventors using the wet method, when the cleaning with pure water after processing was insufficient, a phenomenon was observed in which the recording bit was easily broken or corrosion proceeded rapidly. As a result, in the experiments of the wet method performed by the present inventors, the yield of the formation of the cylindrical bit may be deteriorated as compared with the method described first.

When a magnetic field is applied to the columnar bit in the longitudinal direction (in the direction of the film surface of the magnetic disk), no morphological change occurs, but when a magnetic field is applied in a direction perpendicular to the film surface, the shape is changed in the length direction of the column. The recording bit lengthens. This is shown in FIG. FIG. 5 shows that when a magnetic field is applied in the longitudinal direction, the recording bit does not extend in the longitudinal direction of the cylinder,
It is shown that when a magnetic field is applied in a direction perpendicular to the film surface, the recording bit extends in the length direction of the cylinder.

After recording predetermined data on such a magnetic disk with a magnetic head and then reproducing the data, a reproduced signal is:
This is shown in the graph of FIG. In FIG. 6, as in FIGS. 2 and 3, the horizontal axis represents the position in the track direction.
The vertical axis represents the signal intensity. In this figure, a broken line indicates a thermal asperity signal, and a solid line indicates a magnetic flux signal, that is, a reproduced signal by ordinary magnetic recording. Arrows in the vertical direction in the drawing indicate that the direction of magnetization is perpendicular to the film surface, and arrows in the horizontal direction indicate that the direction of magnetization is parallel to the film surface. .

As shown in FIG. 6, in a longitudinal recording in which a magnetic field is applied in the longitudinal direction, only a magnetic signal is detected as a reproduction signal, and in a perpendicular recording in which a magnetic field is applied perpendicularly to the film surface, the reproduction is performed. The signal has a thermal asperity signal superimposed on the magnetic recording signal.

Further, it was confirmed that the data recording was certainly performed for each of the columnar recording bits by 2 bits of the digital signal. Thus, according to the third embodiment, the diameter of the recording bit is 0.1
With a micron diameter, quaternary recording can be performed on each recording bit.

As described above, in the third embodiment, each cylinder and the recording bit are the same, and each cylinder has two data bits.
Although bits are recorded, it is also preferable to apply a magnetic field so that the same data is recorded on a plurality of cylinders.

In the third embodiment, the magnetization / morphological recording layer 3 is made of an Fe-Rh alloy. However, it is preferable to use a Mn-Ga alloy. This is as described in the second embodiment.

[Fourth Embodiment] In the magnetic disk (recording medium) described in the third embodiment, it is necessary to reduce the number of recording bits and at the same time to increase the amount of change in shape when magnetized in the vertical direction. R needs to be increased.

However, when a thin columnar bit of 0.05 μm or less was formed, a phenomenon was found that the columnar bit was broken or damaged, so that sufficient recording / erasing characteristics could not be obtained. This is because the magnetic head repeatedly collides with the recording bit several hundred thousand times or more in contact recording and reproduction.

When a cylindrical bit is formed by processing, the surface area exposed to the atmosphere increases. Therefore, a phenomenon was observed in which the corrosion of the surface progressed faster with time as compared with the conventional magnetic disk. That is, deterioration due to aging was observed.

Therefore, in the fourth embodiment, the columnar magnetic / morphological recording layer 13 is formed on the nonmagnetic ceramic layer 12 in order to improve the repetitive recording / erasing resistance and to suppress the progress of corrosion of the recording bit. There is a structure to be embedded in. FIG. 7 is an explanatory view of a structure in which the magnetic / morphological recording layer 13 is embedded in the nonmagnetic ceramic layer 12.
As shown in this figure, in the fourth embodiment, a cell (hole) formed to a diameter of 0.05 micron and a depth of 50 nm by fine processing is provided in the nonmagnetic ceramics layer 12, and a magnetic field is formed in this cell. The structure in which the morphological recording layer 13 is embedded is adopted. The material of the nonmagnetic ceramics layer 12 is A
l ₂ O ₃ is used. The magnetic / morphological recording layer 13 is
An Fe-Rh alloy or a shape memory alloy MnGa is used.

The magnetic disk according to the fourth embodiment is manufactured as follows. First, a non-magnetic ceramic layer 12 made of Al ₂ O ₃ is formed on a substrate 1 by a sputtering method. A fine pattern is formed on the non-magnetic ceramic layer 12 by electron beam exposure. This fine pattern is specifically a cylindrical hole. After that, an Fe—Rh or Mn—Ga alloy is formed on the nonmagnetic ceramic layer 12 by using a sputtering method. The Fe-Rh or Mn-Ga alloy is formed not only inside the hole but also outside the hole, and the formed portion other than the hole is removed by a reverse sputtering method or a wet method. In this way, a magnetic disk (recording medium) as shown in FIG. 7 is manufactured.

After predetermined data was recorded on this recording medium (magnetic disk) by a magnetic head, the data was reproduced by the magnetic head. FIG. 8 is a graph showing the reproduced signal. In FIG. 8, as in FIGS. 2 and 3,
The horizontal axis indicates the position in the track direction, and the vertical axis indicates the signal intensity. In this figure, a broken line indicates a thermal asperity signal, and a solid line indicates a magnetic flux signal, that is, a reproduced signal by ordinary magnetic recording. Arrows in the vertical direction in the drawing indicate that the direction of magnetization is perpendicular to the film surface, and arrows in the horizontal direction indicate that the direction of magnetization is parallel to the film surface. .

As shown in FIG. 8, when data is recorded by applying a magnetic field in the longitudinal direction parallel to the film surface, the reproduced signal contains only this magnetic signal. on the other hand,
When data is recorded by applying a magnetic field in a direction perpendicular to the film surface, a thermal asperity signal appears superimposed on a magnetic recording signal in a reproduction signal. As a result, when the magnetic recording signal and the thermal asperity signal are combined, 4
And four-level recording can be realized.

It was also confirmed that noise was reduced as compared with the recording medium of the third embodiment. Also, as compared with the recording medium of the third embodiment, the reproduced signal deteriorates with time by repeatedly reproducing the data. It was confirmed that the length was almost 100 times longer than the recording medium of the third embodiment. As a result, according to the fourth embodiment, the reliability of the recorded information can be improved.

[Fifth Embodiment] The recording medium of the fourth embodiment can perform high-density recording and has high reliability. However, since fine processing is required during the manufacturing process, it may be difficult to form a uniform bit pattern on the nonmagnetic ceramic layer 12 having a radius of about 6 cm. The smaller the size of the "hole" produced by the fine processing, the greater the variation in the size of the "hole". As a result, the case where the magnitude of the reproduced signal of the data to be recorded is not uniform is also assumed.

Therefore, in the fifth embodiment, a magnetic disk using the substrate 11 on which the pyramid-shaped protrusions 22 having a uniform size are formed is used.

In the fifth embodiment, InP / InAs is used as the material of the substrate 11. In the substrate 11 using InP / InAs, pyramid-shaped protrusions 22 having a size of several nm are naturally formed uniformly on a flat substrate. In the fifth embodiment, a magnetic disk is formed by depositing an Fe—Rh alloy or a Mn—Ga alloy on the substrate 11.

FIG. 9 is an explanatory diagram showing the configuration of a recording medium (magnetic disk) according to the fifth embodiment. As shown in this figure, a pyramid-shaped projection 22 made of InAs is naturally formed on a substrate 11 made of InP. The magnetization / configuration memory layer 3 is provided so as to fill the space between the pyramid-shaped protrusions 22. The magnetization / morphological memory layer 3 is made of an Fe-Rh alloy or a Mn-Ga alloy as described above.

In the fifth embodiment, the recording bit in which data is recorded is the portion 3a of the magnetization / configuration memory layer 3 which fills the space between the pyramid-shaped projections 22. Therefore, the size of each recording bit becomes about several nm. Note that, in FIG. 9, a hatched circle is drawn on the magnetic disk, and this circle schematically represents the recording bit.

However, in this recording medium (magnetic disk), data is recorded every several tens of recording bits. In other words, the same data is recorded every tens of recording bits. This is because the recording bits are extremely small.

According to the fifth embodiment, the controllability of the morphological change is good. Here, the controllability of the form change means that the form of the recording bit can be changed as intended. In the fifth embodiment, since the recording bit is extremely small,
This is because data can be recorded virtually anywhere on the surface of the magnetic disk.

On the other hand, in the third embodiment and the like, the recording bit is one cylinder, and one type of data is recorded for each cylinder. Therefore, unless a magnetic field is accurately applied to the position of the cylinder, the form of the recording bit cannot be changed satisfactorily. In other words,
If the position where the magnetic field is applied deviates from the cylinder, good control of the shape change cannot be achieved.

As described above, in the fifth embodiment, since the surface of the magnetic disk is composed of recording bits everywhere, it is possible to realize good controllability of the form change without precise alignment. .

Therefore, according to the experiments of the present inventors,
Compared with the embodiments described so far, four-value recording with lower recording noise was realized. This is shown in the graph of FIG. 10 and FIG.
Similarly, the horizontal axis represents the position in the track direction, and the vertical axis represents the signal intensity. In this figure, a broken line represents a thermal asperity signal, and a solid line represents a magnetic flux signal, that is, a reproduced signal by ordinary magnetic recording. Arrows in the vertical direction in the drawing indicate that the direction of magnetization is perpendicular to the film surface, and arrows in the horizontal direction indicate that the direction of magnetization is parallel to the film surface. .

[Sixth Embodiment] The recording medium of the fifth embodiment has low noise and is suitable for realizing high-density multi-level recording. However, since the material of the substrate 11 used is rare, it may be difficult to obtain it. In addition, special equipment is required for processing, and the manufacturing equipment may become more complicated.

Therefore, it is desirable to realize a low-noise recording medium similar to that of the fifth embodiment by using a material that is easily available and can be easily manufactured. In the sixth embodiment, such a recording medium will be described.

The recording medium in the sixth embodiment is the same as the substrate 2
The plastic substrate 21 on which the pyramid protrusion 32 having a size of several nm is formed as 1 is used. Then, a recording medium is manufactured by forming a Fe—Rh alloy or a Mn—Ga alloy on the substrate 21. An explanatory diagram showing the structure of this recording medium is shown in FIG. As shown in this figure, the structure in which the pyramid-shaped protrusions 32 are provided on the substrate 21 is basically the same as in the fifth embodiment. The sixth embodiment is different from the fifth embodiment in that these structures use plastic.

FIG. 12 is a graph showing a state of a reproduced signal after predetermined data is recorded on the recording medium by the magnetic head. 12 and FIG. 3 and FIG.
Similarly, the horizontal axis represents the position in the track direction, and the vertical axis represents the signal intensity. In this figure, a broken line represents a thermal asperity signal, and a solid line represents a magnetic flux signal, that is, a reproduced signal by ordinary magnetic recording. Arrows in the vertical direction in the drawing indicate that the direction of magnetization is perpendicular to the film surface, and arrows in the horizontal direction indicate that the direction of magnetization is parallel to the film surface. .

In the portion where longitudinal recording was performed in which a magnetic field was applied in a direction parallel to the film surface, only a magnetic signal was detected. In the portion where perpendicular recording was performed in which a magnetic field was applied in a direction perpendicular to the film surface, a magnetic signal was detected. A signal in which a thermal asperity signal was superimposed was detected.

Therefore, as in the above-described embodiments, it was confirmed that quaternary recording was possible by combining the magnetic signal and the shape change. Further, it was confirmed that a reproduced signal having a sufficient intensity could be obtained even when the recording bit size was set to about 0.05 μm.

The reproduced signal of the recording medium according to the sixth embodiment has a slightly larger noise than the recording medium according to the fifth embodiment. This is considered to be due to the following reasons. InP substrate 11 described in the fifth embodiment
Is smooth on the order of nm or less.
The InAs pyramid-shaped protrusion 22 formed on the upper surface can make the size of the protrusion and the interval between the protrusions uniform and uniform.

However, the plastic substrate 21 in the sixth embodiment has irregularities on the surface on the order of several tens of nm. In addition, when the magnetic disk is observed over one track, surface undulations of about several microns are observed.
Further, the size of the pyramid-shaped projections 32 cannot be made as uniform as in the fifth embodiment, although it depends on the processing accuracy of the plastic.

Due to the existence of such unevenness and undulation, noise is larger in the sixth embodiment than in the InP substrate magnetic disk in the fifth embodiment. However, there is an effect that four-level recording can be performed using a material that is easily available as compared with the fifth embodiment.

[Seventh Embodiment] The configuration of a multi-valued recorded data reproducing system used for reproducing data in each of the above-described embodiments will be described.

FIG. 13 is a configuration diagram showing the configuration of this multi-valued recorded data reproduction system. An MR magnetic head 42 is provided in contact with the multi-valued magnetic recording medium 40. This MR magnetic head 42 performs contact reproduction.
The signal from the MR magnetic head is a signal including a magnetic recording signal and a thermal asperity signal, as described in the above embodiment. By performing contact reproduction with the MR magnetic head 42, a magnetic recording signal and a thermal asperity signal at a certain recording bit can be detected simultaneously.

The signal processing section 44 performs predetermined signal processing, separates a thermal asperity signal and a magnetic recording signal, and recognizes a morphological change and a direction of magnetization based on these signals. That is, the MR magnetic head 42 and the signal processing unit 44 correspond to the magnetization direction detecting means and the form change detecting means in the claims. Further, the signal processing unit 42 reproduces the recorded multi-value data based on the magnetization direction and the morphological change, and outputs the data to the outside. With the above configuration, the multi-value data recorded on the medium 40 on which multi-value recording has been performed can be reproduced.

[0095]

According to the present invention, using a medium having a magnetization / morphological recording layer according to the present invention, multi-value recording can be performed by combining a magnetic signal and a morphological change, and a high-density magnetic recording medium can be manufactured. In addition, if the magnetic material is formed as a projection on the substrate, a morphological change can be reliably generated, and stable multi-value recording with less noise can be performed.

Further, from such a multi-valued magnetic recording medium,
In the system for reproducing data, since the morphological change and the magnetic direction are detected at the same time, the recorded quaternary data can be reproduced. In particular, if the reproduction is performed with an MR head, the thermal asperity signal can be detected efficiently, and the morphological change can be efficiently detected via the thermal asperity signal.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of a magnetic disk medium according to an embodiment.

FIG. 2 is an explanatory diagram showing reproduction signals when a recording medium having a magnetic / morphological recording layer made of an Fe—Rh alloy is contact-reproduced by an MR magnetic head.

FIG. 3 is an explanatory diagram showing a reproduction signal when a recording medium having a Mn—Ga alloy as a magnetic / morphological recording layer is contact-reproduced by an MR magnetic head.

FIG. 4 is an explanatory diagram showing a recording bit shape of a magnetic disk in which a magnetic / morphological recording layer is processed into a column shape in a direction perpendicular to a film surface.

FIG. 5 is an explanatory diagram showing a change in the form of a cylindrical bit when magnetized in a longitudinal direction and a vertical direction with respect to the cylindrical bit.

FIG. 6 is an explanatory diagram showing a reproduced signal when contact reproduction is performed on the disk of FIG. 4 by an MR magnetic head.

[FIG. 7] Non-magnetic ceramics Al ₂ O ₃ is finely processed to 0.0
FIG. 3 is an explanatory diagram showing a configuration of a recording medium in which a magnetization / shape recording layer is embedded in a cell (hole) formed to have a diameter of 5 microns and a depth of 50 nm.

FIG. 8 is an explanatory diagram showing a reproduced signal when contact reproduction is performed on the medium of FIG. 7 by an MR magnetic head.

FIG. 9 is an explanatory diagram showing a configuration of a multi-valued magnetic recording medium in which a magnetization / morphological recording layer is formed on a substrate in which pyramid-shaped protrusions InAs having a size of several nm are formed on the surface of an InP substrate.

FIG. 10 is an explanatory diagram showing a reproduced signal when the recording medium of FIG. 9 is contact-reproduced by an MR magnetic head.

FIG. 11 is an explanatory diagram showing a configuration of a multi-valued magnetic recording medium in which a Fe-Rh alloy or a Mn-Ga alloy is formed on a plastic substrate having pyramid protrusions having a size of several nm formed on the surface thereof. .

FIG. 12 is an explanatory diagram showing a reproduction signal when the recording medium of FIG. 11 is contact-reproduced by an MR magnetic head.

FIG. 13 is a configuration diagram illustrating a configuration of a multilevel magnetic recording data reproduction system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Crystal orientation control layer 3 Fe-Rh magnetic / morphological recording layer 3a Mn-Ga magnetic / morphological recording layer 3b Part of magnetic / morphological recording layer 4 Protective layer 5 Lubrication layer 11 Substrate 12 Nonmagnetic ceramics layer 13 Magnetic / morphological Recording layer 21 Substrate 22 Pyramidal projection 32 Pyramidal projection 40 Multilevel recording medium 42 MR magnetic head 44 Signal processing unit

Claims (16)

[Claims] 1. A magnetic recording medium including a recording layer for recording data, wherein the recording layer is a magnetic material whose volume expands and contracts when a magnetic field is applied, and the volume expands and contracts according to the direction of the magnetic field. A multi-valued magnetic recording medium comprising a magnetic material having a determined direction, wherein a combination of a morphological change of the magnetic material and a magnetization direction of the magnetic material is used as a recording state. 2. The method according to claim 1, wherein the magnetic material is processed into a columnar shape to form a columnar protrusion, a plurality of the columnar protrusions are arranged on the substrate, and each of the columnar protrusions changes in shape when a magnetic field is applied. 2. The multi-valued magnetic recording medium according to claim 1, wherein the multi-valued magnetic recording medium has a recording state based on a combination of a change in magnetization direction. 3. The recording layer according to claim 1, wherein a plurality of cylindrical holes having a predetermined diameter are formed in a substrate made of a non-magnetic material, and the recording material is formed by embedding the magnetic material in the holes. Multi-valued magnetic recording medium. 4. The multi-valued magnetic recording medium according to claim 3, wherein said substrate is made of non-magnetic ceramics. 5. The multi-valued magnetic recording medium according to claim 3, wherein the diameter of the hole is approximately 0.1 μm. 6. A recording layer comprising a substrate having a plurality of protrusions formed on a surface thereof, wherein the magnetic material is provided on a surface of the substrate having the protrusions formed thereon to form the recording layer. Item 8. The multi-valued magnetic recording medium according to Item 1. 7. The semiconductor device according to claim 6, wherein the substrate is made of InP, and the protrusion is made of InAs.
The multivalued magnetic recording medium according to the above. 8. The multi-valued magnetic recording medium according to claim 6, wherein said substrate is made of plastic, and said projections are also made of plastic. 9. The multi-valued magnetic recording medium according to claim 6, wherein the projection has a quadrangular pyramid shape with a size of several nm. 10. The multi-valued magnetic recording medium according to claim 1, wherein the magnetic material is an Fe—Rh alloy. 11. The multi-valued magnetic recording medium according to claim 1, wherein said magnetic material is a magnetic shape memory alloy. 12. The multi-valued magnetic recording medium according to claim 11, wherein said magnetic shape memory alloy is Mn—Ga. 13. A magnetization direction detecting means for detecting a magnetization direction of each recording bit in a recording layer of a multi-valued magnetic recording medium, and a form change detecting means for detecting a form change of each recording bit in the recording layer. Wherein the detection of the magnetization direction and the detection of the morphological change are performed simultaneously on the same recording bit. 14. The morphological change detecting means detects the morphological change via a thermal asperity signal, and the magnetization direction detecting means detects the magnetization direction through a magnetic flux change of a magnetic recording signal. Claim 1
3. The multivalued magnetic recording data reproduction system according to 3. 15. The multi-valued magnetic recording data reproducing system according to claim 13, wherein said morphological change detecting means and said magnetization direction detecting means are MR magnetic heads. 16. The multi-valued magnetic recording data reproducing system according to claim 15, wherein said MR magnetic head performs contact reproduction on said multi-valued magnetic recording medium.