JPH08235578A - Magnetic recording medium and magnetic recording and reproducing device using the medium - Google Patents

Abstract

PURPOSE: To provide a magnetic recording medium having a function to suppress stiction under a wide range of humidity conditions. CONSTITUTION: The magnetic recording medium MM consists of a glass substrate 1, base layer 2, magnetic layer 3 and protective layer 6. The protective layer 6 consists of TiO2 fine particles 4 which can induce photocatalytic reaction and has a texture function to decrease stiction between a magnetic head slider and the magnetic recording medium MM, and a fine particle holding layer 5 to hold the TiO2 fine particles 4 on the magnetic layer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus for recording and reproducing information by relatively moving a magnetic head and a magnetic recording medium, and a magnetic recording medium used for the same.

[0002]

2. Description of the Related Art As is well known, a magnetic recording / reproducing apparatus is an apparatus for recording / reproducing information on / from a magnetic recording medium by a magnetic head. A hard disk device is one of the magnetic recording / reproducing devices. In a hard disk device, the magnetic head and the magnetic recording medium are in a contact friction state when the hard disk device is started or stopped, and the magnetic head transitions to a floating state after the hard disk device is started (hereinafter referred to as CSS system). Called) is mainly adopted.

A hard disk device using the CSS method has raised the following tribological problem in principle. First, the head slider and the magnetic recording medium are in a complete contact state when the hard disk device is started and stopped, but the surfaces of both are subjected to ultra-precision finishing. For this reason, the two are attracted to each other, and the attraction force makes it impossible to rotate the spindle on which the magnetic recording medium is mounted, so that the hard disk device itself cannot be activated (hereinafter referred to as stiction problem).
Occurs. Further, as a second problem, in the contact friction state between the head slider and the magnetic recording medium, the frictional force generated between them causes the surface abrasion damage of the head slider or the magnetic recording medium. Due to this cause, there is a so-called head crash phenomenon in which when the wear damage of the magnetic recording medium reaches the magnetic layer, the information recorded in the magnetic layer is destroyed.

In order to solve the above-mentioned stiction problem and head crash problem, the following measures have been conventionally applied to the magnetic recording medium. That is, between the head slider and the magnetic recording medium (Head Disk Interface,
(Hereinafter referred to as "HDI") to reduce the contact area and reduce the adsorption of both, a mechanical texture that creates unevenness on the substrate surface of the magnetic recording medium by a wrapping tape method,
As described in JP-A-3-113823, a glass substrate is chemically treated (chemical etching) to create irregularities on the substrate surface. An underlayer and a magnetic layer are laminated on the textured substrate to prevent the magnetic layer itself from sliding directly on the head slider and to improve the wear resistance of the magnetic recording medium. As a result, a protective layer made of carbon, metal oxide, carbide, or nitride is overcoated on the magnetic layer, and a liquid lubricant such as perfluoropolyether (PFPE) is applied on the protective layer. .

[0005]

In recent years, due to downsizing of computers and diversification of software to be used, computers are required to be marketed at a higher speed and with a large capacity. Accordingly, a magnetic recording / reproducing apparatus with a larger capacity and a higher recording density has been demanded accordingly. In addition, the computer is used in an environment where the temperature and humidity change from a normal office where the temperature and humidity are relatively stable, and the temperature and humidity change irregularly and in a wide range (due to the portable computer, it can be used outdoors. The frequency of use has increased, and there is a need for a magnetic recording / reproducing device that operates stably without depending on such environmental changes.

[0006] However, it is technically possible to achieve both the high recording density of the magnetic recording / reproducing device and the improvement of the stable operability of the magnetic recording / reproducing device in a wide range of environment by the technique disclosed heretofore. It is known that there are difficulties, and the details will be described below.

First, in order to increase the density of the magnetic recording / reproducing apparatus, the distance between the magnetic sensor provided on the magnetic head slider and the upper surface of the magnetic layer formed on the magnetic recording medium (hereinafter referred to as the effective flying height). Note) must be reduced. In response to this demand, the height of the above-mentioned texture is reduced on the magnetic recording medium side to reduce the variation in the effective flying height depending on the location to stably record and reproduce information, and to provide it on the magnetic layer. It is necessary to take measures such as reducing the thickness of the protective layer provided.

[0008] The texture itself is often provided directly on the medium substrate mainly for the purpose of reducing the contact area of HDI and reducing the adsorption of both. It is a well-known fact that attempts to reduce the texture height are widely made by those skilled in the art, as described in, for example, JP-A-2-214014 (formation of surface irregularities by mechanical texturing). Is. However, in the mechanical texturing method of mechanically processing the substrate surface of the magnetic recording medium, the heights of the irregularities formed on the magnetic recording medium are inevitably uneven,
It is difficult to keep the effective flying height constant. In addition, even if the flying height of the head slider itself is reduced, the flying stability is impaired by the head slider coming into contact with the surface protrusions that are abruptly present, resulting in unstable recording / reproducing characteristics. There was a problem with magnetic properties. In addition to that, a problem has also been raised that damage to the magnetic recording medium is likely to be induced from the point of sudden contact. Therefore, on the other hand, a method that is completely different from the texturing method is used to form surface irregularities with a uniform projection height and small amplitude that can reduce the effective flying height (with respect to the head slider flying direction).
A method of performing the above has also been proposed (see, for example, Japanese Patent Laid-Open No. 4-89616).

However, even if the surface unevenness having a uniform height as described above is advantageous in increasing the recording density, a new technique is required in accordance with a change in the environment in which the magnetic recording / reproducing apparatus is used. Problem (above stiction problem) occurs.

In the stiction problem, humidity is particularly important as a factor causing the stiction problem.
As described in s.Magn., Vol.26, 2487 (1990), the amount of water adsorbed on the head slider and the magnetic recording medium is an important influential factor that directly affects the above-mentioned "stiction". Becomes In addition, the stiction at high humidity has a stronger adsorption force than that at room temperature and normal humidity, and in the worst case, the spindle on which the magnetic recording medium is mounted may be completely unbootable. . In order to reduce this stiction under high humidity, it is necessary to make it difficult for the HDI to aggregate adsorbed water. However, in the above-described magnetic recording medium in which the projection height is uniform and the surface unevenness having a small amplitude is formed in the head slider flying direction, the contact area of the head slider / magnetic recording medium is increased, and Aggregation of adsorbed water is likely to occur as nuclei, so that the stiction resistance is deteriorated.

As described above, in order to increase the recording density of the magnetic recording medium by improving the conventional technique of reducing the surface roughness of the magnetic recording medium, the trade-off is that the stiction resistance is inevitably sacrificed. There is a relationship between the two. Therefore, under the present circumstances, there is a need for a magnetic recording medium that achieves this technical breakthrough, enables the head slider to have a low flying height, and is unlikely to induce stiction under high humidity.

Therefore, in view of the above-mentioned conventional problems, an object of the present invention is to provide a magnetic recording medium having an excellent stiction suppressing function under a wide range of humidity conditions and a magnetic recording / reproducing apparatus using the same. Especially.

Another object of the present invention is to provide a magnetic recording medium having a head horn preventing function and a magnetic recording / reproducing apparatus using the same.

Still another object of the present invention is to provide a magnetic recording medium capable of lowering the flying height of a head slider and a magnetic recording / reproducing apparatus using the same.

[0015]

In order to solve the above-mentioned problems, a magnetic recording medium according to the present invention comprises (Structure 1) at least a magnetic layer provided on a non-magnetic substrate,
A magnetic recording medium in which a protective layer is directly or indirectly provided on the upper surface of the magnetic layer is characterized in that the protective layer contains a material having a water decomposition catalyst function and a texture function.

As an aspect of this configuration 1, (configuration 2) In the magnetic recording medium of configuration 1, as the main component of the protective layer, a photocatalytic reaction can be induced and stiction between the magnetic head slider and the magnetic recording medium. And a second material for holding the first material on the upper surface of the magnetic layer.

Further, the magnetic recording / reproducing apparatus according to the present invention has (Structure 3) the magnetic recording medium according to Structures 1 and 2 mounted, and for desorbing adsorbed moisture on the surface of the magnetic recording medium by a photocatalytic reaction. It is characterized by being equipped with a light source of.

[0018]

In the present invention, according to the above-mentioned constitutions 1 and 3, by providing the protective layer with a water decomposition catalyst function,
It has become possible to obtain a magnetic recording medium that has an excellent stiction suppressing function under a wide range of humidity conditions and that can easily reduce the flying height of the head slider.

First, since the protective layer contains the first material, and the magnetic recording / reproducing apparatus is equipped with a light source for inducing a photocatalytic reaction, the adsorbed moisture on the magnetic recording medium is removed. It has a first function of decomposing by a photocatalytic action and reducing the amount of water itself on the medium surface, and by having the above-described texture function, the contact area between the magnetic head slider and the magnetic recording medium is reduced, By having the second function that makes it difficult for water to aggregate, it is possible to further reduce stiction.

In addition, the first material can reduce the unevenness of the created surface irregularities and can reduce the height itself of the protrusions as compared with the conventional mechanical texture method. As a result, it is possible to reduce the fluctuation of the distance between the magnetic head slider and the magnetic layer that are being floated, that is, the effective flying height when recording / reproducing information on / from the magnetic recording medium. In addition, by removing the factor that remarkably deteriorates the flying stability of the head slider, that is, the generation of abnormal protrusions due to the texture processing, it has become possible to stably perform high-density recording / reproduction on the magnetic recording medium.

The second material contained in the protective layer is
By having the role of firmly holding the first material on the magnetic layer, it has the role of improving the mechanical durability of the protective layer itself, and by covering the entire surface of the magnetic layer, the corrosion resistance of the magnetic layer is improved. It also has the function of maintaining sex.

[0022]

EXAMPLES First, the main constitutions and manufacturing methods of Examples and Comparative Examples will be described, and then their tribological characteristics will be compared and described.

[Embodiment] FIG. 1 shows a magnetic recording medium MM according to an embodiment of the present invention. The magnetic recording medium MM in this example was manufactured as follows.

First, the glass substrate 1 having a diameter of 65 mm is R
After mirror-polishing so that the _max becomes 3 nm or less, the glass substrate 1 is cleaned with pure water and a purity of 9
After ultrasonic cleaning in 9.9% or more isopropyl alcohol (IPA) for 20 minutes and leaving it in IPA vapor for 5 minutes,
Dried. Then, the underlayer 2 and the magnetic layer 3 were formed on the glass substrate 1 that has undergone the washing process by the RF magnetron sputtering method. At this time, Cr was deposited as the underlayer 2 on the glass substrate 1 to a thickness of 100 nm, and CoNiCr was deposited to a thickness of 50 nm as the magnetic layer 3 on the underlayer 2. The underlayer 2 and the magnetic layer 3 are under the same sputtering conditions (atmosphere gas: Ar gas with a purity of 99.9% is used, gas pressure: 10 m).
Torr, gas flow rate: 10 SCCM, input power: 200
W, back pressure: 10 ⁻⁷ Torr, no substrate heating).

Next, TiO ₂ fine particles 4 having an average particle diameter of 20 nm were dispersed on the surface of the magnetic layer 3 by the dipping method. At that time, IPA with a purity of 99.9% (1000 m
After preparing a solution in which 1 mg of TiO ₂ fine particles was mixed in 1), the disk sample was immersed in the solution for 1 minute,
The TiO ₂ fine particles were dispersed on the surface of the magnetic layer 3 by gradually pulling up from the solution at a pulling rate of 1.4 mm / sec.

Next, on the TiO ₂ fine particles 4 and the magnetic layer 3 to form a particulate protective layer 5 made of carbon by RF magnetron sputtering method, a protective layer 6 together with TiO ₂ particles 4. At this time, the atmosphere gas has a purity of 9
Using 9.9% argon gas and CH ₄ gas, gas pressure: 5 mTorr (gas flow rate, Ar: 10 SCCM, C
H ₄ : 5SCCM), input power: 100W, back pressure: 10
^The film was formed under the conditions of ^-7 Torr and no substrate heating. After the formation of the fine particle protective layer 6, the reactive ion etching method (gas: CF ₄ , gas flow rate: 30 SCCM, RF power: 200 W, back pressure: 3 × 10 ^-2 Torr, etching time: 1 minute) was used. When the fine particle protective layer 5 is formed, Ti
After the excess carbon deposited on the O ₂ fine particles 4 was removed, a magnetic recording medium MM of this example was obtained. Further, the surface roughness of the magnetic recording medium MM in this example was measured by a stylus type roughness meter (manufactured by Rank Taylor Hobson: Tally step, stylus: 0.1 μm × 2.5 μm pyramidal type, measuring force:
As a result of evaluation by 2 mgf, RMS (root mean square roughness) was 3 nm.

[Comparative Example] FIG. 2 shows a comparative example of a magnetic recording medium. The magnetic recording medium MM 'was manufactured as follows.

First, the glass substrate 7 having a diameter of 65 mm is R
After mirror-polishing so that the _max becomes 3 nm or less, the glass substrate 7 is cleaned with pure water and a purity of 9
After ultrasonic cleaning in 9.9% or more isopropyl alcohol (IPA) for 20 minutes and leaving it in IPA vapor for 5 minutes,
Dried. Then, on the glass substrate 7 that has undergone the cleaning process,
Texture layer 8, underlayer 9, magnetic layer 10, protective layer 11
Were consistently produced by the RF magnetron sputtering method. The texture layer 8 has a low melting point of Al
Argon gas with a purity of 99.9% is used as the atmosphere gas, and the gas pressure is 5 mTorr (gas flow rate, Ar: 10 SC
CM, CH ₄ : 5 SCCM), input power: 100 W, back pressure: 10 ⁻⁷ Torr, substrate heating temperature: 200 ° C.

Next, 100 nm of Cr was laminated as the underlayer 9 on the texture layer 8, and the magnetic layer 10 was formed on the underlayer 9.
As a result, CoNiCr was laminated in a thickness of 50 nm. The underlayer 9 and the magnetic layer 10 are under the same sputtering conditions (atmosphere gas: Ar gas with a purity of 99.9% is used, gas pressure: 10).
mTorr, gas flow rate: 10 SCCM, input power: 20
0 W, back pressure: 10 ⁻⁷ Torr, no substrate heating).

As the protective layer 11, carbon was laminated on the magnetic layer 10 to have a thickness of 10 nm. At that time, argon gas and CH ₄ gas having a purity of 99.9% were used as the atmosphere gas, and the gas pressure was 5 mTorr (gas flow rate, Ar: 10 SCCM, C
H ₄ : 5SCCM), input power: 100W, back pressure: 10
After the film formation was performed under the conditions of ^-7 Torr and no substrate heating, a magnetic recording medium MM 'of this comparative example was obtained. Further, the surface roughness of the magnetic recording medium MM 'in this comparative example was measured by a stylus type roughness meter (Rank Taylor Hobson: Tally step, stylus: 0.1 μm × 2.5 μm pyramidal type, measuring force: 2
As a result of evaluation by mgf), RMS (root mean square roughness) is 3
was nm.

FIG. 3 schematically shows a magnetic recording / reproducing apparatus equipped with the magnetic recording medium MM manufactured in the above embodiment.

This magnetic recording / reproducing apparatus has a spindle unit 1
2, magnetic head 13, magnetic head holder 14, light source 1
5 and the control circuit unit 16. The spindle unit 12 holds the magnetic recording medium MM and drives it to rotate. The magnetic head 13 slides or floats on the magnetic recording medium MM to perform magnetic recording on the magnetic recording medium MM or reproduce a magnetic recording signal recorded on the magnetic recording medium MM. The magnetic head holder 14 holds the magnetic head 13 and controls the position of the magnetic head 13 with respect to the magnetic recording medium MM. The light source 15 irradiates the surface of the magnetic recording medium MM with light from an oblique direction (10 ° with respect to the surface) in order to decompose the adsorbed moisture on the surface of the magnetic recording medium MM by a photocatalytic reaction. The control circuit unit 16 controls the spindle unit 12, the magnetic head 13, the magnetic head holding unit 14, and the light source 15. As the light source 15, a light source that can generate light (electromagnetic wave) from ultraviolet light having a wavelength of 200 to 750 nm to visible light is used.

Further, in order to demonstrate the effect of the present invention, FIG.
In addition, in order to perform the initial friction force measurement for evaluating the degree of stiction, in addition to the configuration of the magnetic recording / reproducing apparatus, the magnetic head holding unit 14 is equipped with a strain gauge sensor 17, and the strain gauge sensor 17 is used. 1 shows a magnetic recording / reproducing device equipped with a device (strain amplifier 18, personal computer 19) for monitoring the detected initial frictional force.

FIG. 5 shows the magnetic recording / reproducing apparatus shown in FIG. 4 equipped with the magnetic recording medium MM of the embodiment of the present invention and the magnetic recording medium MM 'of the comparative example, which is installed in a thermo-hygrostat. The temperature is constant at 50 ° C and the relative humidity is 10 to 90%.
R. It shows the initial coefficient of friction when changed to H. In this test, after the inside of the constant temperature and humidity chamber where the magnetic recording / reproducing device is installed reaches a predetermined humidity, the CSS operation (takeoff and landing of the head slider on the magnetic recording medium) is performed in the pattern shown in FIG. Based on the slider levitation curve 20 (change in friction force observed during head slider levitation with respect to disk rotation time, see FIG. 7) obtained at that time, the value of the initial friction force 21 observed at the start of disk rotation is determined. The initial friction coefficient was calculated by dividing by the head load described later. The magnetic head used for the measurement was IB
M3370 type in-line type magnetic head, head load 6.5gf, head slider material Al ₂ O ₃
-Made of TiC.

As a result, the magnetic recording medium MM of the example and the magnetic recording medium MM 'of the comparative example show almost the same initial friction coefficient when the optical excitation by the light source 15 equipped in the magnetic recording / reproducing apparatus is not carried out. 80% R.I. It can be seen that in a humidity environment exceeding H, the initial friction coefficient sharply increases, and remarkable stiction occurs between the magnetic head slider and the magnetic recording medium. On the other hand, when the light is emitted from the light source 15, the initial friction coefficient is significantly reduced in the magnetic recording medium MM of the embodiment, especially in a high humidity environment (≧ 70% RH), and the effect of the present invention is proved. Has been done.

As shown in FIG. 8, the TiO ₂ fine particles on the magnetic recording medium MM having a photocatalytic function are obtained by irradiating the surface of the magnetic recording medium MM described in the example with light from an oblique direction. 4, electrons are generated in the light irradiation part 22 (valence band) and holes are generated in the non-irradiation part 23 (conduction band). Moisture electrons generated in the conduction band is adsorbed on reducing power higher magnetic recording medium on ^{_{MM (H 2 O → H +}} + OH -) in hydrogen H ₂ and reduction of H ⁺ of, generated during the valence band The holes have a high oxidizing power and oxidize OH ⁻ to generate oxygen O ₂ through the generation of H ₂ O ₂ , and as a result, the adsorbed moisture is decomposed. As a result, the true contact portion between the magnetic head slider and the magnetic recording medium (in this case, the moisture tends to agglomerate and the meniscus effect (effect of attracting both the magnetic head slider and the magnetic recording medium) due to the moisture is likely to occur. , Magnetic head slider / TiO ₂ fine particles), the amount of adsorbed water itself that exhibits the meniscus effect is reduced, and it is considered that the stiction is significantly reduced.

As a combination of the first material having a texture function and a photocatalytic function, SnO ₂ , ZnS, ZnO, WO ₃ , SrT is used in addition to the combination of the materials described in the examples.
iO ₃ , SiC, CdS, Fe ₂ O ₃ , GaP, CdS
e or the like can be used, and also for the holding layer (second material) holding the first material, the materials (SiO ₂ , ZrO ₂ , Al ₂ O ₃ , Y) proposed in the prior art are used.
₂ O ₃ , In ₂ O ₃ , SnO ₃ , Ta ₂ O ₅ , MgO,
Cr ₂ O ₃ , La ₂ O ₃ , SiC, WC, TiC, C ₃
The use of oxides such as N ₄ , S ₃ N ₄ , BN and TiN, carbides, nitride ceramics and the like and combinations thereof is not excluded. Further, there is no limitation on the method of forming the protective layer, and in addition to the combined use of the sputtering and dipping methods used in this example, for example, a wet or dry process such as a sol-gel method, a CVD method, an evaporation method, or a combination thereof. It is possible to form a film.

Further, the magnetic recording medium MM in the present embodiment.
Although a lubricating layer is not formed on the upper part, it is possible to apply each of the lubricants proposed in the prior art including perfluoropolyether (PFPE).

In this embodiment, the protective layer 6 is laminated on the magnetic layer 3 at room temperature, but in order to further improve the sliding resistance and the corrosion resistance of the magnetic layer, an intermediate layer between them is used. Layers may be provided. Further, although not applied in the present embodiment, it is possible to add a substrate heating process or a film forming preliminary process such as a bias voltage to the substrate in the film forming process of the underlayer, the magnetic layer and the protective layer.

Although the glass substrate 1 is used as the non-magnetic substrate in this embodiment, it may be an Al alloy substrate, a ceramics substrate, a plastic substrate, a carbon substrate, or the like.
The present invention can be applied regardless of the substrate specifications such as substrate material, size, and thickness.

Although CoNiCr is used for the magnetic layer 3 in the present embodiment, the magnetic layers already disclosed in the prior art, for example, CoCrTa, CoCrPt, CoPtN.
A Co-based magnetic material such as i or Fe-based magnetic material may be used.

In the present embodiment, the light source 15 provided in the magnetic recording / reproducing apparatus irradiates the surface of the magnetic recording medium MM from an oblique direction (10 ° to the surface of the magnetic recording medium MM). Depending on the surface roughness created on the surface of the recording medium MM, the magnetic head slider surface roughness, and the degree of stiction reduction, this irradiation angle is set to 0 to 90 °.
It can be freely set between. Further, in this embodiment, the light source 15 is directly provided inside the magnetic recording / reproducing apparatus. However, for example, the light source main body is provided as a separate device, and the light from the light source main body is introduced into the magnetic recording / reproducing apparatus by an optical fiber. The same effect as that of the present invention can be obtained even if the above method is adopted.

Further, the magnetic recording medium manufactured in the present invention is not limited to the application to the recording system by the complete flying type magnetic head, but is also a pseudo contact recording system (Quasi-Contact Recording).
) Alternatively, it can be used for a contact recording method.

[0044]

As is clear from the above description, the protective layer itself has both the adsorption moisture decomposition catalyst function and the texture function, thereby having an excellent stiction suppressing function under a wide range of humidity conditions. Moreover, it is possible to obtain a magnetic recording medium in which the flying height of the magnetic head slider can be easily reduced.

[Brief description of drawings]

FIG. 1 is a sectional view showing a layer structure of a magnetic recording medium according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a layer structure of a magnetic recording medium of a comparative example.

FIG. 3 is an internal perspective view showing an outline of a magnetic recording / reproducing apparatus according to the present invention.

4A and 4B are an internal perspective view and a block diagram in which a magnetic recording / reproducing apparatus according to the present invention is equipped with a strain gauge sensor for measuring a frictional force and a frictional force monitoring device.

FIG. 5 is a diagram showing a relationship between relative humidity and initial friction coefficient for magnetic recording media of Examples and Comparative Examples.

FIG. 6 is a diagram showing a CSS pattern in a CSS test.

FIG. 7 is a diagram showing a flying curve of a magnetic head slider.

FIG. 8 is an explanatory diagram of a mechanism of a water decomposition catalyst function in the present invention.

[Explanation of symbols]

1 Glass Substrate 2 Underlayer 3 Magnetic Layer 4 TiO ₂ Fine Particles 5 Fine Particle Retaining Layer 6 Protective Layer 7 Glass Substrate 8 Texture Layer 9 Underlayer 10 Magnetic Layer 11 Protective Layer 12 Spindle Part 13 Magnetic Head 14 Magnetic Head Holding Part 15 Light Source 16 Control Circuit part 17 Strain gauge sensor 18 Strain amplifier 19 Personal computer 20 Slider levitation curve 21 Initial friction force 22 Light irradiation part (valence band) 23 Non-irradiation part (conduction band) 24 Irradiation light MM Magnetic recording medium

Claims (3)

[Claims] 1. In a magnetic recording medium in which at least a magnetic layer is provided on a non-magnetic substrate, and a protective layer is provided directly or indirectly on the upper surface of the magnetic layer, the protective layer has a water decomposition catalyst function and a texture function. A magnetic recording medium comprising a material having: 2. A first material having, as a main component of the protective layer, a texture function capable of inducing a photocatalytic reaction and reducing stiction between a magnetic head slider and a magnetic recording medium, and the first material. The magnetic recording medium according to claim 1, further comprising a second material for holding a material on the upper surface of the magnetic layer. 3. A magnetic recording medium comprising the magnetic recording medium according to claim 1 or 2, and a light source for decomposing adsorbed moisture on the surface of the magnetic recording medium by a photocatalytic reaction. Playback device.