JPH0316690B2 - - Google Patents

Description

[Detailed description of the invention]

1. Field of Industrial Application The present invention relates to a method for manufacturing magnetic recording media such as magnetic tapes and magnetic disks. 2. Prior Art Conventionally, this type of magnetic recording medium has been widely used for recording various electrical signals such as video, audio, and digital signals. These have been developed as a system that uses magnetization in the in-plane longitudinal direction of a magnetic layer (magnetic recording layer) formed on a substrate. However, in recent years, with the increase in the density of magnetic recording, recording methods that use magnetization in the longitudinal direction in the plane have a tendency to increase the demagnetizing field within the medium as the recording signal becomes shorter in wavelength, resulting in attenuation and rotation of the residual magnetization. This causes a significant decrease in playback output. For this reason, it is extremely difficult to reduce the recording wavelength to submicron or less. On the other hand, a perpendicular magnetization recording method that uses magnetization in the thickness direction of the magnetic layer of a magnetic recording medium (so-called perpendicular magnetization) has recently been proposed (for example, "Nikkei Electronics" August 7, 1978 issue No. .192).
According to this recording method, as the recording wavelength becomes shorter, the demagnetizing field that acts on the residual magnetization in the medium decreases, so it has favorable characteristics for increasing density, and is essentially suitable for high-density recording. This method is considered to be suitable for Incidentally, in order to perform such perpendicular recording efficiently, the recording layer of a magnetic recording medium must have an axis of easy magnetization in the perpendicular direction (thickness direction of the magnetic layer). Such a magnetic recording medium is a coated type in which a magnetic coating mainly composed of magnetic powder and a binder is coated on a substrate (support), and the axis of easy magnetization is oriented in the perpendicular direction of the magnetic layer. The medium is known. This applied media includes Co,
Fe ₃ O ₄ , γ-Fe ₂ O ₃ , Co-added Fe ₃ O ₄ , Co-added γ-
Fe ₂ O ₃ , hexagonal ferrite (e.g. barium ferrite), MnBi, etc. are used as magnetic powders (JP-A-52-46803, JP-A-53-67406, JP-A-52-
Publications No. 78403, No. 55-86103, and No. 54-87202). However, in these coated media, there is a limit to increasing the packing density of magnetic powder due to the presence of a non-magnetic binder in the magnetic layer, and therefore it is difficult to increase the S/N ratio sufficiently. I can't. Moreover, the magnitude of the recorded signal is limited by the size of the magnetic particles, and thus a medium having a magnetic layer made of a magnetic coating is unsuitable for perpendicular magnetization recording. Therefore, continuous thin film magnetic recording media, in which a perpendicularly magnetized magnetic layer is formed by continuously adhering a magnetic material onto a support without using a binder, are attracting attention as suitable for high-density recording. ing. This continuous thin film type perpendicular magnetization recording medium is
For example, as disclosed in Japanese Patent Publication No. 57-17282, it has a magnetic recording layer made of an alloy film of cobalt and chromium, and in particular, a Co-Cr alloy film with a chromium content of 5 to 25% by weight is used. It is said to be excellent.
Furthermore, a magnetic recording material having a magnetic layer made by adding 30% by weight or less of rhodium to a Co-Cr alloy film is disclosed in JP-A-55-111110;
Vanadium alloy film (e.g. Institute of Electrical and Electronics Engineers of America: abbreviated as IEEE journal “Transaction on
Magnetism" 1982 Vol. 18 No. 6, p. 1116) and cobalt-ruthenium alloy films (for example, the 18th Tohoku University Research Symposium "Perpendicular Magnetic Recording" Paper Collection held in March 1982). Are known. Among these, Co--Cr alloy films are considered promising for perpendicular magnetization, but have been found to have the following drawbacks. (1) In order to orient the axis of easy magnetization perpendicular to the plane of the magnetic layer, it is necessary to create the magnetic layer in a high vacuum of 10 ^-7 Torr or higher, and the substrate must be subjected to advanced cleaning treatment and low sputtering speed. etc., and the control factors in the vertical direction become extremely complicated. (2) When recording and reproducing signals, the magnetic recording medium and the perpendicular recording/reproducing head are moved relative to each other, so the interface between the head and the medium is poor and scratches are likely to occur on the medium. , the head may also be damaged. (3) Since the magnetic layer is hard, cracks tend to occur when the magnetic layer is provided on a flexible substrate. (4) Corrosion resistance as a magnetic recording medium is insufficient;
Therefore, it is necessary to provide a protective film on the surface. Therefore, the present applicant filed a patent application No. 53-23042 to develop a perpendicular magnetic recording medium that completely eliminates these drawbacks.
It has already been proposed as a No. The invention related to this earlier application is
The magnetic layer is (a) a continuous magnetic layer whose main component is iron oxide. (b) Residual magnetization (M _H ) in the in-plane direction of the magnetic layer,
Residual magnetization in the direction perpendicular to the plane of the magnetic layer (M _V )
The ratio (M _V /M _H ) is 0.5 or more. (c) The specific crystal axis of the iron oxide is oriented substantially in the positional direction with respect to the in-plane direction of the magnetic layer. It is characterized by having the following as a configuration. According to the invention related to this earlier application, since the magnetic layer has iron oxide as the main component, excellent properties unique to oxides (mechanical strength, chemical stability, etc.) can be obtained, and compared to the conventional The surface protective film required for alloy thin films is no longer required. As a result, the distance between the magnetic head and the medium can be reduced, making it possible to perform high-density recording, and also to reduce costs in terms of materials. Moreover, the residual magnetization (M _V /M _H ) in the in-plane direction and perpendicular direction of the magnetic layer whose main component is iron oxide is
Since the value is 0.5 or more, the magnetic moment of the iron oxide magnetic material rises in the perpendicular direction by 30 degrees or more with respect to the in-plane direction, and the structure is such that perpendicular magnetization can be sufficiently realized. The residual magnetization amounts M _V and M _H can be measured, for example, with a sample vibrating magnetometer (manufactured by Toei Kogyo Co., Ltd.). That is, if M _V /M _H is less than 0.5, it is difficult to obtain a magnetic moment suitable for perpendicular magnetization. Furthermore, what is important is that the specific crystal axis of the iron oxide is oriented in a direction substantially perpendicular to the in-plane direction of the magnetic layer, so that the structure can obtain the perpendicular magnetization characteristic sufficiently and with good reproducibility. This is what is happening. Especially when Fe ₃ O ₄ is used as iron oxide,
For example, it is extremely important that the [111] direction of the crystal axis is perpendicular to the plane (particularly that it has a spinel structure). When the iron oxide has a spinel crystal structure, the amount of saturation magnetization is large, and the residual magnetic flux density is large during reproduction of recorded signals, resulting in extremely good reproduction sensitivity. In general, iron oxides exhibiting magnetism include γ-Fe ₂ O ₃ which has rhombohedral parasitic ferromagnetism; Fe ₃ O ₄ and γ-Fe ₂ O ₃ which have a spinel structure and ferrimagnetism, or their bertolide compounds. ; Ba, a hexagonal iron oxide
ferrite, Sr ferrite, Pb ferrite or derivatives thereof; rare earth garnet type ferrite with garnet structure. Among these iron oxides, the saturation magnetization, which is one of the important magnetic properties, is 2.0 Gauss for α-Fe ₂ O ₃ , Ba ferrite,
For Sr ferrite and Pb ferrite, the maximum
It is about 380 Gauss, and even more so for garnet type ferrite, it is 140 Gauss at most. On the other hand, the saturation magnetization of spinel ferrite preferably used in the present invention is 480 Gauss, which is the largest among iron oxides. Such a large amount of saturation magnetization is extremely effective when reproducing a recorded signal because it ensures a sufficient residual magnetic flux density and improves reproduction sensitivity. On the other hand, Ba
There are ferrite and Sr ferrite, but in order to form these continuous thin-film magnetic layers, the temperature of the substrate must be maintained at a high temperature of 500°C, for example in the sputtering equipment described below, and for this reason, the type of substrate must be There are problems with the manufacturing conditions, such as restrictions on the production conditions (for example, the use of plastic substrates with poor heat resistance cannot be used), and the method is inappropriate. Spinel type iron oxide, which is preferably used, allows film formation at a low temperature of room temperature to 300° C., and is not subject to restrictions on the substrate material. Here, the magnetic layer is fundamentally different from conventional coated magnetic layers in that it is made of iron oxide (e.g. Fe ₃ O ₄ , γ-Fe ₂ O ₃ , or a non-chemical composition intermediate to these) without using a binder. The bertolide compound (which has a stoichiometric composition) itself consists of a continuous series of thin films. In this magnetic layer, the sum of both elements iron and oxygen is preferably 50% by weight or more, and 70% by weight of the magnetic layer.
It is desirable that the amount is at least % by weight. Further, the ratio of iron to oxygen is preferably 1 to 3 (number of oxygen atoms/number of iron atoms), and even more preferably 4/3 to 2.
The iron oxides listed above are suitable. However, metals other than iron and oxygen, or oxides thereof, nonmetals, semimetals, or compounds thereof, etc. are added to the magnetic layer.
This determines the magnetic properties of the magnetic layer (e.g. coercive force,
It is possible to improve the amount of saturation magnetization, the amount of residual magnetization), its crystallinity, and the orientation of the crystal in a specific axis direction. These additive elements or compounds include Al,
Co, Co−Mn, Zn, Co−Zn, Li, Cr, Ti, Li−
Cr, Mg, Mg-Ni, Mn-Zn, Ni, Ni-Al, Ni
-Zn, Cu, Cu-Mn, Cu-Zn, V, etc., but it is preferable to use other than rare earth elements. In addition, the base materials that can be used for magnetic recording media are:
Various materials can be used as long as magnetic materials can be attached thereto. For example, plastics such as polyethylene terephthalate, polyvinyl chloride, cellulose triacetate, polycarbonate, polyimide, polyamide, polymethyl methacrylate, ceramics such as glass, etc. can be used. Furthermore, Mg, Al, Si, Ti, V, Cr, Mn, Fe, CO,
Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ru, Te,
Metals such as Ta and W, semimetals, and alloys thereof can also be used. The shape of the base is sheet, card,
In addition to disks and drums, it may also be in the form of a long tape. To produce this magnetic recording medium, the substrate can be closely supported on a fixed plate, or the magnetic material can be applied while the substrate is traveling. For this purpose,
A sputtering method, vapor deposition method, etc. is applied in which a target of magnetic material is sputtered in a processing chamber connected to an evacuation system such as a vacuum pump, or the material is evaporated from a magnetic material evaporation source and deposited on a substrate. It is possible. In either case, the elements constituting the magnetic layer are blown away to form a continuous thin film on the substrate. As a result of studying the invention related to the above-mentioned prior application, the present inventor discovered a medium with further improved perpendicular magnetic recording characteristics, and arrived at the present invention. 3. Purpose of the invention In addition to the effects achieved by the invention of the earlier application, the purpose of the present invention is to improve the coercive force by incorporating cobalt in a specific range into the iron oxide constituting the continuous magnetic layer. (Hc) and improved perpendicular magnetic anisotropy and perpendicular alignment without causing demagnetization. 4 Structure of the invention and its effects That is, the present invention contains cobalt in an amount of 0.05 to 10 atomic%.
By the opposed target sputtering method using iron contained as a target material, the mixed gas pressure of inert gas and oxygen was set to 10 ^-4 to ^{10 -2} Torr, and the partial pressure ratio (oxygen/inert gas) was As 2-90%,
(a) The ratio (M _V /M H ) of the remanence ratio in the in-plane direction (M _H ) to the remanence ratio (M _V ) in the _direction perpendicular to the surface is 1.0 or more. (b) Contains 0.05 to 10 atomic% cobalt, Fe ₃ O ₄ ,
The present invention relates to a method for manufacturing a magnetic recording medium that forms a continuous magnetic thin film containing iron oxide as a main component of γ-Fe ₂ O ₃ or an intermediate composition thereof. According to the present invention, an iron oxide-based magnetic layer exhibiting M _V /M _H of 1.0 or more is formed, similar to the invention related to the earlier application, so that the same effects and effects as described in the invention related to the earlier application are obtained. A magnetic recording medium that is suitable for high-density perpendicular magnetic recording and has excellent mechanical strength, chemical stability, etc. can be obtained. Furthermore, since the continuous magnetic thin film containing iron oxide as the main component contains 0.05 to 10 atomic% (percentage of atoms) of cobalt, it is clear from the data described below. It is possible to increase Hc and significantly improve perpendicular magnetic anisotropy and orientation. On the other hand, if cobalt is less than 0.05 atomic%, Hc decreases, perpendicular magnetic anisotropy and orientation become extremely poor, and
If it exceeds 10 atomic%, Hc will increase, but pressure demagnetization and heating demagnetization will occur. It is further desirable that the above cobalt content be 0.5 to 5 atomic%. Note that the type and composition of iron oxide, substrate material, film forming method, etc. used in the present invention may be the same as those of the invention related to the earlier application described above. 5 Examples Hereinafter, the present invention will be explained in more detail with reference to the drawings. A facing target sputtering method is used as a means for depositing the magnetic material used in the present invention onto a substrate. FIG. 1 shows a high frequency discharge type facing target sputtering device. In the drawing, 1 is a vacuum chamber, 2 is an evacuation system consisting of a vacuum pump etc. for evacuating the vacuum chamber 1, and 3 is an exhaust system that introduces a predetermined gas into the vacuum chamber 1 to raise the gas pressure to 10 ^-1 ~
This is a gas introduction system set at approximately 10 ^-4 Torr. The target electrodes are configured as opposed target electrodes in which a pair of targets T ₁ and T ₂ are separated from each other by a target holder 4 and are placed facing each other in parallel. A magnetic field is formed between these targets by magnetic field generating means (not shown). On the other hand, the substrate 6 on which the magnetic thin film is to be formed is placed by the substrate holder 5 perpendicularly to the side between the opposing targets. In a sputtering device configured like this,
A magnetic field is formed in a direction perpendicular to the surfaces of both targets T ₁ and T ₂ facing each other in parallel, and this magnetic field creates a gap between the plasma atmosphere generated between the targets T 1 and T 2 and the cathode fall area (i.e., the plasma atmosphere generated between the targets T ₁ and T _{2 )} . The γ electrons emitted by the impact of sputtering gas ions accelerated by the electric field on the target surface in the region between _T1 and _T2 ) are trapped in the space between the targets and moved toward the other opposing target . The γ electrons that have moved to the other target surface are reflected by the cathode fall section nearby. In this way, the γ electrons repeatedly move back and forth between the targets T ₁ and T ₂ while being constrained by the magnetic field. During this reciprocating motion, the γ electrons collide with the neutral atmospheric gas to generate ions and electrons of the atmospheric gas, and these products promote the release of γ electrons from the target and the ionization of the atmospheric gas. . Therefore, the target
A high-density plasma is formed in the space between T ₁ and _{T 2} , and the target material is sufficiently sputtered and deposited as a magnetic material on the lateral substrate 6 . Compared to other flying methods, this facing target sputtering device enables film formation at a high deposition rate using high-speed sputtering, and the substrate is not directly exposed to plasma, allowing film formation at low substrate temperatures. This method is advantageous for forming a perpendicularly magnetized film. Furthermore, the incident energy of the magnetic film material sputtered onto the substrate by the facing target sputtering device is smaller than that of a normal sputtering device, so the material is easily deposited directionally in the desired direction, and the material can be deposited vertically. It becomes easier to obtain a film with a structure suitable for magnetization recording. Next, a specific example of producing a magnetic recording medium using the above sputtering apparatus will be described. The conditions for this preparation were as follows. Target material Iron (Co from 0.05
Substrate Glass Distance between opposing targets 100mm Magnetic field in sputtering space 150Oe Target shape 100mm diameter disk (5mm thickness) Distance between substrate and target end 40mm Back pressure in vacuum chamber 8×10 ^-7 Torr Introduced gas Ar＋O ₂ Introduced gas pressure 4×10 ^-3 Torr (Ar3×
10 ^-3 TorrO ₂ 1×10 ^-3 Torr) Sputter input power 500W (high frequency 13.56M
Hz) In this way, a predetermined amount (0.05 to 10 atomic%) of Co is deposited on the pace film 6, as shown in FIG.
Iron oxide magnetic layer 10 made of Fe ₃ O ₄ containing
A magnetic recording medium having the following properties was obtained. For this medium, the thickness of the magnetic layer is, for example, 1500 Å (according to an open-type film thickness meter: Talystep, manufactured by Rank Taylor Hobson), and its characteristics are identified by composition identification using an X-ray microanalyzer (XMA),
The state of iron oxide was determined by line diffraction, and the magnetic properties were determined by a sample vibrating magnetometer. The characteristics of the obtained magnetic recording medium were as follows. First, the ratio of the residual magnetization in the in-plane direction (M _H ) to the residual magnetization in the perpendicular direction (M _V ) is M _V /
M _H ≧1.0. That is, as illustrated in FIG. 3, a hysteresis curve for magnetization in the in-plane direction shown by the broken line and a hysteresis curve for magnetization in the perpendicular direction shown by the solid line are obtained, but when the applied magnetic field is zero, The amount of magnetization at that time was defined as M _H and M _V. According to this, the former hysteresis curve is smaller than the latter hysteresis curve, and M _V ≧1.0M _H (i.e. M _V /
It is clear that M _H ≈1.6), which indicates that a magnetic layer suitable for perpendicular magnetization is formed. The coercive force was 920 oersted in the vertical direction and 750 oersted in the in-plane direction. This is a surprising fact for iron oxide magnetic layers. In order to compare with the experiment described above, the target material was pure iron (without Co) under the above production conditions.
As a result of sputtering _in a similar _manner as
It was 500 oersted in the in-plane direction. In addition, the composition of this magnetic recording medium was measured using an XMA (X-ray microanalyzer: "X-556" manufactured by Hitachi, Ltd.).
When measured using a KEVEX-7000 model, it was found that Fe was the main peak and a certain amount of Co was included. Furthermore, in order to investigate the state of iron oxide, an X-ray diffraction device (JDX-10RA manufactured by JEOL Ltd.: CuKα
As a result, an X-ray diffraction spectrum as shown in Figure 4 was obtained (substrate temperature during sputtering was 270°C, magnetic film thickness was 1500Å, Ar
Gas pressure is 3×10 ^-3 Torr, oxygen gas pressure is 1×
10 ^-3 Torr and contains 1 atomic% cobalt
Fe ₃ O ₄ film formation). According to this, the easy axis of magnetization of Fe ₃ O ₄ rises perpendicular to the in-plane direction of the magnetic layer, and in particular, the [111] direction of its crystal axis is oriented perpendicular to the plane. I understand. In addition, for the magnetic layer prepared at the above gas pressure (10 ^-1 to ^{10 -4} Torr), the composition and degree of orientation of the film were measured using an X-ray diffraction device (JDX-10RA manufactured by JEOL Ltd.). did. As a result, as shown in Figure 5,
Reflection peaks of Fe ₃ O ₄ and γFe ₂ O ₃ were observed. According to this, the reflection peaks on the (111) plane of Fe ₃ O ₄ and its higher-order planes are caused by the gas pressure (Ar + O ₂ )
When the temperature is 10 ^-2 to 10 ^-4 Torr (particularly 10 ^-2 to 10 ^-3 Torr), it is possible to obtain a structure in which Fe ₃ O ₄ is substantially oriented in the [111] direction. Figure 6 shows the relationship between the reflection intensity on the (111) plane of Fe ₃ O ₄ (corresponding to the vertical axis in Figure 5) and the perpendicular magnetization orientation (M _V /M _H ) of the magnetic layer. This is the data. According to this, reflection intensity is increased (however,
Let the maximum value of the peak value of the (111) plane be 100%. )but
When it is about 50% or more, M _V /M _H ≧1.0 is obtained, indicating that the magnetic layer is capable of perpendicular magnetization.
Correspondingly, in Figure 5, the reflection intensity is 50%.
It can be seen that the gas pressure should be lower than 10 ^-2 Torr to obtain more than 10 -2 Torr. Therefore, based on this fact, in order to form a magnetic layer for perpendicular magnetization according to the present invention, Ar +
The mixed gas pressure of O ₂ should be between 10 ^-4 and 10 ^-2 Torr, but since the plasma becomes unstable at gas pressures lower than 10 ^-4 Torr, the lower limit of the gas pressure must be set.
10 ^-4 Torr, and at higher gas pressures than 10 ^-2 Torr, the reflection intensity ratio (that is, the degree of vertical orientation) becomes smaller.
It becomes impossible to satisfy the requirement of M _V /M _H ≧1.0. Furthermore, the mixing ratio of Ar + O ₂ gas is also important, and as shown in Figure 7, M _V /M _H changes depending on the O ₂ /Ar partial pressure ratio, especially when the partial pressure ratio is less than 2%. It was found that M _V /M _H is less than 1.0.
Also, if the partial pressure ratio is too high and exceeds 90%, the discharge will become unstable, so the above partial pressure ratio should be between 2 and 90%, and particularly preferably between 10 and 80%. . In addition to the above-mentioned Ar gas, there are also other gases for spatsuta.
There are Kr, Ne, He, etc., but this sputtering gas can be introduced alone (however, the target in this case is iron oxide), or it can be mixed with the above-mentioned O ₂ , N ₂ , H ₂ O, etc. may also be used. In addition, the degree of vacuum for preliminary evacuation before sputtering is 5x.
It is desirable to do this so that the pressure is 10 ^-5 Torr or less. In addition, the various formation conditions mentioned above (e.g. gas pressure, etc.)
By changing , it is possible to obtain a magnetic recording medium according to the present invention having magnetic properties different from those of the previous example (FIG. 3). This medium also exhibits good perpendicular magnetization characteristics. Next, the anisotropy of the Co-containing Fe ₃ O ₄ film formed as described above was investigated. For example, using cobalt as a target
0atomic%, 0.05atomic%, 1atomic%,
Five types of Fe disks (purity 99.9%, 100 mmφ) containing 2 atomic% and 3 atomic% were used to form magnetized films with a thickness of 1650 Å by reactive sputtering in an Ar+O ₂ mixed gas. For these, the resistivity was measured using the two-terminal method, the perpendicular anisotropy Ku (=K⊥+2πMs ² ) was measured using a torque meter (Ha=10KOe), and the coercive force Hc and saturation magnetization Ms were measured using a sample vibrating magnetometer (maximum applied magnetic field). = 10KOe). These results are shown below. First, the resistivity ρ of the Fe ₃ O ₄ film strongly depends on its degree of oxidation (corresponding to the voltage applied to the target). Figure 8 shows the changes in coercive force Hc⊥ (solid line) and Hc (broken line) in the perpendicular and in-plane directions with respect to ρ, and Hc⊥ reaches its maximum value when ρ is around 1 to 10 Ω-cm. , vertical anisotropy was induced in this vicinity. In addition, the value of Hc⊥ is influenced by the Co content, and the Co-doped one shows a higher Hc⊥ than the non-doped one, which is within the range of the present invention (Co content
0.05 atomic% or more), the vertical anisotropy increases. Figure 9 shows the 4πMs dependence (at10KOe) of the perpendicular anisotropy Ku, and when 4πMs is in the range of 2.5 to 4.5KG, Ku shows a large value, and the perpendicular anisotropy magnetic field Hk⊥ also becomes large. I understand. In particular, in the case of Co doping (≧0.05 atomic%), Ku gradually improves. Next, the dependence of the perpendicular anisotropic magnetic field Hk⊥ on the (111) plane orientation was investigated. However,
(111) is expressed by the following equation. (111)=P ⁽¹¹¹⁾ −Po ₍₁₁₁₎ /1−Po ₍₁₁₁₎ (However,

【formula】

It is. I (hkl) and Io (hkl) are the diffraction intensities of the film sample and the powder sample, respectively, and this value is 1 in the case of perfect plane orientation, 0 in the case of disorder, and 0 when the other planes are oriented. Although it is negative, all negative values are set to 0 here. ) Moreover, this (111) can be controlled by the conditions for forming the magnetic film, that is, the pressure (Ar, O ₂ ), discharge power, and substrate temperature. In particular, the pressure is 10 ^-1 ~
Good results (M _V /M _H ≧0.5) can be obtained at 10 ^-4 Torr, a discharge voltage of 100 V or less, and a substrate temperature of 500°C or less.
Figure 10 shows the (111) dependence of Hk⊥.
According to this, in the case of Co non-doping, it is better to set (111)≧0.8 to improve Hk⊥ (0 or more), but in Co-doping (≧0.05 atomic%), (111) should be made even smaller. The amount of Co doping is
At 3atomic%, (111) should be 0.3 or more. As described above, it has been confirmed that the film created by the sputtering method in this example shows relatively large perpendicular anisotropy in the Fe ₃ O ₄ phase, and that a film with Hk⊥ reaching as high as 4KOe can be obtained. (Especially when the Co doping amount is ≧0.05 atomic %, more preferably 1 to 5 atomic %). Figure 11 shows the dependence of Hk⊥ on the heat treatment temperature Ta. Hk⊥ reaches its maximum amount around Ta = 200°C and disappears around 350°C (the crystal structure at this time is γ-Fe ₂ O ₃ ). Also, according to this, in the case of Co-non-doping, in order to obtain Hk⊥, room temperature≦Ta≦300°C should be satisfied, but it is understood that Co-doping can expand the upper limit of Ta. For example, when the Co doping amount is 1 to 5 atomic%, room temperature ≦
It has been suggested that the range can be extended to Ta≦400℃. Also, if Hk⊥ is set to 1.5 or more, very good vertical anisotropy will be obtained, but to obtain this,
The only option is Co doping, and increasing the doping amount
It can be seen that the range of Ta that allows Hk⊥≧1.5 can be set wider.

[Brief explanation of the drawing]

The drawings illustrate the present invention; FIG. 1 is a schematic sectional view of a facing target sputtering device, FIG. 2 is a sectional view of a magnetic recording medium, FIG. 3 is a hysteresis curve diagram of the magnetic recording medium, and FIG. Figure 4 is an X-ray diffraction spectrum diagram, Figure 5 is a graph showing the relationship between gas pressure and reflection intensity ratio, Figure 6 is a graph showing the relationship between reflection intensity ratio and vertical orientation degree, and Figure 7 is a graph showing the relationship between gas pressure and reflection intensity ratio. A graph showing the relationship between the pressure ratio and the degree of vertical orientation, Fig. 8 a graph showing the dependence of coercive force on resistivity, Fig. 9 a graph showing the dependence of perpendicular magnetic anisotropy on 4πMs, and Fig. 10 a graph showing the dependence of perpendicular magnetic anisotropy on resistivity. FIG. 11 is a graph showing the dependence of the directional magnetic field on the (111) plane orientation, and FIG. 11 is a graph showing the dependence of the perpendicular anisotropic magnetic field on the heat treatment. In addition, in the symbols shown in the drawings, 1...vacuum chamber, 2...exhaust system, 3...gas introduction system, 4, 5
...Holder, 6...Base, 10...Magnetic layer,
T ₁ , T ₂ ... targets.

Claims (1)

[Claims] 1. The pressure of a mixed gas of inert gas and oxygen is increased by the opposed target sputtering method using iron containing 0.05 to 10 atomic% of cobalt as a target material.
At a pressure of 10 ^-4 to 10 ^-2 Torr and a partial pressure ratio (oxygen/inert gas) of 2 to 90%, (a) remanent magnetic ratio in the in-plane direction (M _H ); The ratio (M _V /M _H ) to the residual magnetic ratio (M _V ) in the direction perpendicular to the surface is 1.0 or more, (b) contains 0.05 to 10 atomic% of cobalt, Fe ₃ O ₄ ,
A method for manufacturing a magnetic recording medium that forms a continuous magnetic thin film containing iron oxide as a main component of γ-Fe ₂ O ₃ or an intermediate composition thereof.