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FIELD OF THE INVENTION
The present invention relates to a magnetic recording medium, and more specifically, the present invention relates to a magnetic recording medium having excellent noise properties.
BACKGROUND OF THE INVENTION
Most commercially available magnetic recording media are an in-plane magnetic recording media where the magnetic easy axis of the magnetic film is mainly oriented parallel to the substrate. If such an in-plane magnetic recording medium is fabricated to have a high recording density, the bit volume is excessively reduced and the reproduction properties may deteriorate due to a thermal fluctuation effect or the like. Furthermore, it is also known that media with high recording density suffer from an increase in the medium noise due to expansion of the magnetization reversal transition region or the like.
On the other hand, a so-called vertical magnetic recording medium where the magnetic easy axis in the magnetic film is oriented perpendicularly to the substrate is advantageous in that low noise can be attained even with high recording density. This is because a sharp magnetization transition is formed and as the recording density increases, the demagnetization field is decreased and stabilized. Moreover, high recording density can be attained even when the bit volume is relatively large. As such, the vertical magnetic recording medium is drawing the attention of investigators in this field.
However, the vertical magnetic recording medium has a reproduction waveform different from that of the in-plane magnetic recording medium. More specifically, the isolated waveform is not a single peak type but contains a di-pulse waveform. Accordingly, it is difficult to apply the signal processing system commonly used for in-plane recording media without modification.
To cope with this, a vertical and in-plane composite type magnetic recording medium has been proposed, which comprises both an in-plain magnetic film and a vertical magnetic film. Such structure enables the use of the same signal processing system as used for in-plane magnetic recording media.
In recent years, the demand for magnetic recording media with higher recording density has been increasing and in keeping with this tendency, there is a demand for improved noise properties.
However, conventional magnetic recording media are by no means entirely satisfactory with respect to noise properties, and there is also a demand for magnetic recording media having more excellent noise properties. The present invention has been achieved in consideration of the above problems of the prior art.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a magnetic recording medium adapted for use with the signal processing system commonly used for in-plane magnetic recording media without modification and having excellent noise properties.
The above object has been achieved in a first embodiment of the invention by providing a magnetic recording medium comprising a substrate having thereon an in-plane magnetic film having a magnetic easy axis oriented in the in-plane direction with respect to the substrate and a vertical magnetic film having a magnetic easy axis oriented perpendicularly to the substrate, the in-plane magnetic film being disposed closer to the substrate than the vertical magnetic film and having a coercivity Hc of from 1,500 to 4,000 Oe and a remnant magnetization film thickness product BrT of from 20 to 100 G.mu.m, and the vertical magnetic film having a coercivity Hc of from 1,500 to 4,000 Oe and a thickness of from 100 to 1,000 .ANG..
In this first embodiment, the vertical magnetic film preferably has a thickness of from 100 to 600 .ANG. and the in-plane magnetic film preferably has a remnant magnetization film thickness product BrT of from 20 to 50 G.mu.m.
A separation film comprising a material capable of growing non-epitaxially to the in-plane magnetic film is preferably disposed between the in-plane magnetic film and the vertical magnetic film, and the separation film preferably has a thickness of from 5 to 200 .ANG..
A nonmagnetic intermediate layer having an hcp structure is preferably disposed between the separation film and the vertical magnetic film.
Furthermore, the clearance between the in-plane magnetic film and the vertical magnetic film is preferably from 10 to 500 .ANG..
In a second embodiment, the present invention provides a magnetic recording medium comprising a substrate having thereon an in-plane magnetic film having a magnetic easy axis oriented in the in-plane direction with respect to the substrate and a vertical magnetic film having a magnetic easy axis oriented perpendicularly to the substrate, the in-plane magnetic film being disposed closer to the substrate than the vertical magnetic film, a separation film being disposed between the in-plane magnetic film and the vertical magnetic film, and the separation film containing one or more of Ta, Re, CuTi, SiC, W, NiP, Zr, Ti and C as a main component.
In this second embodiment, the separation film preferably has a thickness of from 5 to 200 .ANG..
A nonmagnetic intermediate layer having an hcp structure is preferably disposed between the separation film and the vertical magnetic film.
Furthermore, an in-plane magnetic film underlayer is preferably disposed at the substrate side of the in-plane magnetic film, and the in-plane magnetic film underlayer preferably contains Cr or an alloy consisting of Cr and one or more of Ti, Mo, W and V, as a main component.
Furthermore, the in-plane magnetic film preferably contains a Co alloy consisting of from 12 to 25 at % of Cr, from 0 to 15 at % of Pt, from 1 to 10 at % of Ta, from 0 to 10 at % of one or more of Zr, Re, Cu and V, and the balance of Co, as a main component.
In a third embodiment, the present invention provides a magnetic recording medium a substrate having thereon an in-plane magnetic film having a magnetic easy axis oriented in the in-plane direction with respect to the substrate, a separation film comprising a material capable of growing non-epitaxially to the in-plane magnetic film, a nonmagnetic intermediate layer having an hcp structure and a vertical magnetic film having a magnetic easy axis oriented perpendicularly to the substrate, the nonmagnetic intermediate layer containing a Co alloy consisting of from 25 to 50 at % of Cr, from 0 to 15 at % of Pt, from 0 to 10 at % of one or more of Ta, Zr, Cu and Re, and the balance of Co, as a main component, and the vertical magnetic film containing a Co alloy consisting of from 16 to 30 at % of Cr, from 0 to 15 at % of Pt, from 2 to 10 at % of Ta, from 0 to 5 at % of Zr and the balance of Co, as a main component.
The nonmagnetic intermediate layer preferably has a thickness of from 20 to 400 .ANG..
Furthermore, the clearance between the in-plane magnetic film and the vertical magnetic film is preferably from 10 to 500 .ANG..
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a partial cross section showing one example of the magnetic recording medium of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows an example of the magnetic recording medium of the present invention. The magnetic recording medium comprises a substrate 1 having formed thereon an in-plane magnetic film underlayer 2, an in-plane magnetic film 3, a separation film 4, a nonmagnetic intermediate layer 5, a vertical magnetic film 6 and a protective film 7 in this order.
For the substrate 1, an aluminum alloy having an NiP-plating film, glass or ceramic may be used.
The surface of the substrate 1 may be subjected to texturing such as mechanical texturing.
The in-plane magnetic film underlayer 2 is disposed so as to orient the c-axis of crystals in the in-plane magnetic film 3 toward the in-plane direction. In view of improvement of the crystallographic orientation in the in-plane magnetic film 3, the underlayer is preferably formed from Cr or a Cr alloy containing Cr as a main component, more preferably from Cr, a Cr/Ti system alloy, a Cr/Mo system alloy, a Cr/W system alloy or a Cr/V system alloy.
Specific examples of the in-plane magnetic film underlayer 2 include a Cr alloy consisting of from 1 to 40 at % of Ti, Mo, W or V and the balance of Cr.
The in-plane magnetic film underlayer 2 preferably has a thickness of from 10 to 1,000 .ANG..
The term "main component" as used in the present invention means that the component is contained in excess of 50 at %.
In the in-plane magnetic film 3, the magnetic easy axis is mainly directed toward the in-plane direction. Specific examples of the material suitable for the in-plane magnetic film 3 include alloys of the Co/Cr system, Co/Cr/Ta system, Co/Cr/Pt/Ta system, Co/Cr/Ni/Pt/Ta system and Co/Cr/Pt/Ta/Zr system.
In particular, a material containing a Co alloy consisting of from 12 to 25 at % of Cr, from 0 to 15 at % of Pt, from 1 to 10 at % of Ta, from 0 to 10 at % of one or more of Zr, Re, Cu and V, and the balance of Co, as a main component is preferred as a material for the in-plane magnetic film 3 in view of improvement of the crystallographic orientation in this film.
The in-plane magnetic film 3 has a coercivity Hc of from 1,500 to 4,000 Oe (preferably from 2,000 to 3,500 Oe).
If the Hc is less than 1,500 Oe, similar to the vertical magnetic recording medium having only a vertical magnetic film, the isolated waveform obtained at the time of reproduction does not form a single peak. It then becomes difficult to apply the signal processing system used for reproduction of a general-purpose in-plane magnetic recording medium.
On the other hand, if the Hc exceeds 4,000 Oe, the recording properties of the in-plane magnetic film 3 readily deteriorate to cause a low reproduction signal output. Furthermore, problems are liable to occur, for example, because the reproduction waveform does not form a satisfactory single peak or the noise increases.
The in-plane magnetic film 3 has a remnant magnetization film thickness product BrT of from 10 to 100 G.mu.m (second and third embodiments of the invention) or a remnant magnetization film thickness product BrT of from 20 to 100 G.mu.m (first embodiment of the invention).
If the BrT is less than 20 G.mu.m, sufficiently high magnetic flux cannot be obtained and similar to the vertical magnetic recording medium having only a vertical magnetic film, the isolated waveform obtained at the time of reproduction does not form a single peak. As a result, it becomes difficult to apply the signal processing system used for reproduction of a general-purpose in-plane magnetic recording medium.
On the other hand, if the BrT exceeds 100 G.mu.m, similar to the in-plane magnetic recording medium having only an in-plane magnetic film, the medium noise increases. Furthermore, the half value width Pw.sub.50 of the reproduction pulse output becomes worse, and it is difficult to obtain sufficiently high output.
The BrT of the in-plane magnetic film 3 is more preferably from 20 to 50 G.mu.m. This is because when the BrT is within this range, the medium noise can be further reduced.
The separation film 4 is disposed to attain good orientation of the c-axis of crystals in the vertical magnetic film 6 toward the direction perpendicular to the substrate. A material capable of growing non-epitaxially to the in-plane magnetic film 3 is used for the separation film 4.
The separation material is preferably a material having a surface free energy higher than the surface free energy of the constituent material of the nonmagnetic intermediate layer 5, or an amorphous material. This is because the crystallographic orientation of the nonmagnetic intermediate layer 5 and vertical magnetic film 6 formed on the separation film 4 can be improved and the medium noise ascribable to disorder in the magnetic anisotropy of the vertical magnetic film 6 can be minimized.
The separation material preferably contains one or more of Ta, Re, CuTi, SiC, W, NiP, Zr, Ti and C as a main component.
The "CuTi" as used herein means an alloy consisting of Cu and Ti. SiC is a material comprising Si and C and NiP is an alloy consisting of Ni and P.
The separation film 4 preferably has a thickness of from 5 to 200 .ANG..
If the thickness is less than 5 .ANG., the nonmagnetic intermediate layer 5 formed on the separation film 4 is susceptible to influence of the in-plane magnetic film 3 having a crystallographic orientation toward the in-plane direction at the time of film formation. As a result, the crystallographic orientation may become disordered. In that case, the crystallographic orientation of the vertical magnetic film 6 formed on the nonmagnetic intermediate layer 5 is in turn disordered, and consequently the magnetic recording medium thus obtained suffers from an increase in medium noise.
On the other hand, if the thickness exceeds 200 .ANG., the clearance between the in-plane magnetic film 3 and the vertical magnetic film 6 increases and the recording properties of the in-plane magnetic film 3 deteriorate at the time of short wavelength recording.
The nonmagnetic intermediate layer 5 is disposed to attain further improved crystallographic orientation of the vertical magnetic film 6. A nonmagnetic material having a hcp structure is used as the nonmagnetic intermediate layer 5, and a Co/Cr system, Co/Cr/Ta system or Co/Cr/Pt/X (X: one or more of Ta, Zr, Cu and Re) system alloy is preferably used.
In particular, a material containing a Co alloy consisting of from 25 to 50 at % of Cr, from 0 to 15 at % of Pt, from 0 to 10 at % of X and the balance of Co, as a main component is preferred as the nonmagnetic intermediate layer.
If the content of each component of the nonmagnetic intermediate layer 5 is not within the above-described range, the crystallographic orientation of the vertical magnetic film 6 is readily disordered due to mismatching of the lattice of the nonmagnetic intermediate layer 5 with the vertical magnetic film 6. In that case, the magnetic anisotropy of the vertical magnetic film 6 may deteriorate to thereby increase the medium noise.
The nonmagnetic intermediate layer 5 may have a single layer structure or may have a multi-layer structure obtained by laminating a plurality of layers each comprising the above-described material.
The nonmagnetic intermediate layer 5 preferably has a thickness of from 20 to 400 .ANG..
If the thickness is less than 20 .ANG., the crystallographic orientation of the vertical magnetic film 6 is readily disordered at initial growth in the process of forming the vertical magnetic film 6 on the nonmagnetic intermediate layer 5, and the magnetic recording medium thus obtained may suffer from an increase in medium noise.
On the other hand, if the thickness exceeds 400 .ANG., the clearance between the in-plane magnetic film 3 and the vertical magnetic film 6 increases and the recording properties of the in-plane magnetic film 3 deteriorate for short wavelength recording.
The total thickness of the separation film 4 and the to nonmagnetic intermediate layer 5, namely, the clearance between the in-plane magnetic film 3 and the vertical magnetic film 6, is preferably from 10 to 500 .ANG..
If the total thickness is less than 10 .ANG., the crystallographic orientation of the vertical magnetic film 6 is readily disordered and a sufficiently high coercivity may not be obtained, whereas if it exceeds 500 .ANG., the clearance between the in-plane magnetic film 3 and the vertical magnetic film 6 increases and the recording properties of the in-plane magnetic film 3 deteriorate at the short wavelength recording.
In the vertical magnetic film 6, the magnetic easy axis is directed mainly toward a direction perpendicular to the substrate. The material which can be used for the vertical magnetic film 6 includes Co/Cr system, Co/Cr/Ta system, Co/Cr/Pt/Ta system, Co/Cr/Ni/Pt/Ta system and Co/Cr/Pt/Ta/Zr system alloys.
In particular, a material containing a Co alloy consisting of from 16 to 30 at % of Cr, from 0 to 15 at % of Pt, from 2 to 10 at % of Ta, from 0 to 5 at % of Zr and the balance of Co, as a main component is preferred as the vertical magnetic film 6.
If the content of each component of the vertical magnetic film 6 is not within the above-described range, the crystallographic orientation of the vertical magnetic film 6 is readily disordered due to mismatching of the lattice of the vertical magnetic film 6 with the nonmagnetic intermediate layer 5. In that case, the medium noise may increase.
The vertical magnetic film 6 has a coercivity Hc of from 1,500 to 4,000 Oe (preferably from 2,000 to 3,500 Oe).
If the Hc is less than 1,500 Oe, the squareness S (=remnant magnetic flux density Br/saturation magnetic flux density Bs) is reduced, the output decreases and the SNR becomes worse.
On the other hand, if the Hc exceeds 4,000 Oe, the recording properties of the vertical magnetic film 6 disadvantageously deteriorate.
The vertical magnetic film 6 has a thickness of from 100 to 1,000 .ANG..
If the thickness is less than 100 .ANG., a sufficiently high magnetic flux cannot be obtained and similar to the in-plane magnetic recording medium having only an in-plane magnetic film, the medium noise increases. Furthermore, the half value width Pw.sub.50 of the reproduction pulse output becomes worse and sufficiently high output can be difficult to obtain.
On the other hand, if the thickness exceeds 1,000 .ANG., the isolated waveform obtained at reproduction does not form a single peak, and it becomes difficult to apply a signal processing system used in reproduction of a general-purpose in-plane magnetic recording medium.
The thickness of the vertical magnetic film 6 is more preferably from100to 600 .ANG.. This is because when the thickness is within this range, the formation of coarse magnetic particles in the vertical magnetic film 6 can be prevented and the noise Is properties can be further improved.
The protective film 7 is preferably formed from carbon, and preferably has a thickness of from 20 to 100 .ANG..
A lubricating film comprising a perfluoropolyether (PFPE) or the like may also be formed on the protective film 7.
In the manufacture of a magnetic recording medium having the above-described structure, the layers from the nonmagnetic underlayer 2 to the vertical magnetic film 6 can be formed on the substrate 1 by sputtering, vacuum evaporation, ion plating or metal plating. Subsequently, the protective film 7 can be formed by sputtering, a plasma CVD method, an ion beam method or the like.
In the case of forming a lubricating film on the protective film 7, a dipping method or the like may be used.
In an example of a magnetic recording medium of the first embodiment of the invention having the above-described structure, an in-plane magnetic film 3 and a vertical magnetic film 6 are provided. The in-plane magnetic film 3 has a coercivity Hc of from 1,500 to 4,000 Oe and a remnant magnetization film thickness product BrT of from 20 to 100 G.mu.m, and the vertical magnetic film 6 has a coercivity Hc of from 1,500 to 4,000 Oe and a thickness of from 100 to 1,000 .ANG.. By virtue of this constitution, the isolated waveform obtained at reproduction does not form a di-pulse, the signal processing system used in the reproduction of general-purpose in-plane magnetic recording media can be applied, and good noise properties can be obtained while reducing the medium noise ascribable to the expansion of the reversal magnetization transition region or the grain noise resulting from formation of magnetic coarse particles.
Furthermore, by interposing a separation film 4 comprising a material capable of growing non-epitaxially to the in-plane magnetic film 3 between the in-plane magnetic film 3 and the vertical magnetic film 6, the perpendicular orientation of the nonmagnetic intermediate layer 5 and vertical magnetic film 6 formed on the separation film 4 can be improved, the magnetic anisotropy of the vertical magnetic film 6 can be increased, and the medium noise can be reduced.
On the other hand, if a material which grows epitaxially to the in-plane magnetic film 3 is used for the separation film 4, the orientation of the vertical magnetic film 6 may be disordered by the effect of the in-plane magnetic film 3 having in-plane anisotropy.
Also, by interposing a nonmagnetic intermediate layer having an hcp structure between the separation film and the vertical magnetic film, disorder in the orientation at initial growing of the vertical magnetic film 6 can be prevented, the magnetic anisotropy can be increased and the medium noise can be reduced.
In an example of the magnetic recording medium of the second embodiment of the invention having the above-described structure, a separation film 4 is interposed between the in-plane magnetic film 3 and the vertical magnetic film 6. The separation film 4 contains one or more of Ta, Re, CuTi, SiC, W, NiP, Zr, Ti and C as a main component. By virtue of this constitution, the orientation in the perpendicular direction of the nonmagnetic intermediate layer 5 and vertical magnetic film 6 formed on the separation film 4 can be improved, the magnetic anisotropy of the vertical magnetic film 6 can be increased, and the medium noise can be reduced.
The reason why the magnetic anisotropy can be improved when the separation film 4 is formed from the above-described material is not clearly known, however, the following mechanism is considered to participate in this effect.
In the case where SiC, NiP or C is used as the material for the separation film 4, a dangling bond, namely, an unsaturated bond of an atomic group in the periphery of a lattice defect on the surface or inside of the separation film 4, intensifies the bonding strength between the separation film 4 and the nonmagnetic intermediate layer 5 formed thereon. As a result, the crystallographic orientation at the initial growing of the nonmagnetic intermediate layer 5 is improved, the nonmagnetic intermediate layer 5 can have excellent crystallographic orientation in the perpendicular direction, and in turn, the magnetic anisotropy of the vertical magnetic film 6 formed on the nonmagnetic intermediate layer 5 is improved.
Furthermore, the above-described material can grow non-epitaxially to the in-plane magnetic film 3. Accordingly, the orientation of the nonmagnetic intermediate layer 5 and the orientation of the vertical magnetic film 6 are hardly disordered due to the effect of the in-plane magnetic film 3 having in-plane anisotropy.
In the case where Ta, Re, W, CuTi, Ti or Zr is used as the material for the separation film 4, these materials have a surface free energy higher than the surface free energy of the constituent material (for example, Co alloy) of the nonmagnetic intermediate layer 5. Accordingly, the nonmagnetic intermediate layer 5 can be easily (002) oriented at the film formation. This is because when the nonmagnetic intermediate layer 5 in contact with the separation film 4 is (002) oriented, the total surface energy on the interface between the separation film 4 and the nonmagnetic intermediate layer 5 is minimized. The improvement in orientation of the nonmagnetic intermediate layer 5 effects an improvement in orientation of the vertical magnetic film 6 which grows epitaxially to the intermediate layer.
The magnetic anisotropy of the vertical magnetic film 6 is considered to be elevated by the mechanism described above.
Still further, by virtue of a constitution where the in-plane magnetic film underlayer 2 comprises Cr or an alloy consisting of Cr and one or more of Ti, Mo, W and V and the in-plane magnetic film 3 contains a Co alloy consisting of from 1 to 25 at % of Cr, from 0 to 15 at % of Pt, from 1 to 10 at % of Ta, from 0 to 10 at % of one or more of Zr, Re, Cu and V, and the balance of Co, as a main component, the in-plane magnetic film 3 can have good crystallographic orientation and the magnetic recording medium thus obtained can have reduced medium noise.
When a nonmagnetic intermediate layer 5 having an hcp structure is interposed between the separation film 4 and the vertical magnetic film 6, disorder in the orientation at initial growth of the vertical magnetic film 6 comprising a Co alloy or the like having the same hcp structure can be prevented, the magnetic anisotropy thereof can be elevated, and the medium noise can be reduced.
In an example of the magnetic recording medium of the third embodiment of the invention having the above-described structure, an in-plane magnetic film underlayer 2, an in-plane magnetic film 3, a separation film 4 a nonmagnetic intermediate layer 5 and a vertical magnetic film 6 are formed. The nonmagnetic intermediate layer 5 comprises a Co alloy consisting of from 25 to 50 at % of Cr, from 0 to 15 at % of Pt, from 0 to at % of one or more of Ta, Zr, Cu and Re, and the balance of Co. The vertical magnetic film 6 formed thereon comprises a Co alloy consisting of from 16 to 30 at % of Cr, from 0 to 15 at % of Pt, from 2 to 10 at % of Ta, from 0 to 5 at % of Zr and the balance of Co. By virtue of this constitution, the crystallographic orientation of the vertical magnetic film 6 formed on the nonmagnetic intermediate layer 5 is improved.
As a result, the isolated waveform obtained at reproduction does not form a di-pulse, the signal processing system used in reproduction of a general-purpose in-plane magnetic recording medium can be applied, and good noise properties can be obtained while reducing the medium noise ascribable to expansion of the magnetization reversal transition region.
EXAMPLES
Test Example 1
The surface of an aluminum alloy substrate (diameter: 84 is mm, thickness: 0.8 mm) having formed on the surface thereof an NiP plating film (thickness: 15 .mu.m) was subjected to mechanical texturing to have a surface average roughness Ra of 15 .ANG.. The resulting substrate 1 was set in a chamber of a DC magnetron sputtering device (3010, manufactured by ANELVA).
The chamber was evacuated until the ultimate vacuum reached 2.times.10.sup.-7 Pa, the substrate 1 was heated to 200.degree. C., and then on the substrate 1, an in-plane magnetic film underlayer 2 (thickness: 500 .ANG.) comprising Cr-15 at %, Ti-3 at % and Mo (hereinafter referred to as Crl5Ti3Mo), an in-plane magnetic film 3 comprising Co-13 at %, Cr-6 at %, Pt-3 at % and Ta (Co13Cr6Pt3Ta), a separation film 4 comprising carbon, a nonmagnetic intermediate layer 5 comprising Co-40 at % and Cr (Co40Cr) and a vertical magnetic film 6 comprising Co-18 at %, Cr-6 at %, Pt-3 at % and Ta (Col8Cr6Pt3Ta) were sequentially formed by sputtering.
Subsequently, a carbon protective film having a thickness of 100 .ANG. was formed on the vertical magnetic film 6, and then a lubricant was coated on the carbon protective film to form a lubricating film (thickness: 20 .ANG.) comprising PFPE, to thereby obtain a magnetic recording medium.
Test Examples 2 to 4
Magnetic recording media were manufactured by changing the substrate heating temperature at film formation, to thereby vary the coercivity Hc of the in-plane magnetic film 3.
Test Examples 5 to 10
Magnetic recording media were manufactured by varying the BrT of the in-plane magnetic film 3.
Test Examples 11 to 19
Magnetic recording media were manufactured by varying the coercivity Hc or thickness of the vertical magnetic film 6.
Test Example 20
A magnetic recording medium was manufactured in the same manner as in Test Example 16, except that a separation film 4 was not formed.
Test Example 21
A magnetic recording medium was manufactured in the same manner as in Test Example 16, except that a nonmagnetic intermediate layer 5 was not formed.
Test Example 22
A magnetic recording medium was manufactured in the same manner as in Test Example 16, except that a separation film 4 and a nonmagnetic intermediate layer 5 were not formed.
The magnetic recording media of the respective Test Examples were evaluated with respect to magnetostatic properties using vibrating sample magnetometry (VSM). Furthermore, these magnetic recording media were evaluated with respect to recording and reproducing properties using a composite type thin film magnetic head having a magnetoresistive (MR) element in a reproduction unit at a linear recording density of 240 kFCI. The results obtained are shown in Table 1.
In the measurement of SNR (signal noise ratio), the signal was determined with the isolated wave being the measuring object.
TABLE 1
Nonmagnetic
In-plane Separation
Intermediate
Magnetic Film
Layer Vertical Magnetic Film Repro-
Film In-plane Magnetic Film Thick-
Thick- Thick- duction
Underlayer BrT Hc Compo- ness
Compo- ness ness Hc Properties
Composition Composition (G.mu.m) (Oe) sition (.ANG.)
sition (.ANG.) Composition (.ANG.) (Oe) SNR (dB)
Test Cr15Ti3Mo Co13Cr6Pt3Ta 50 645 C 15
Co40Cr 200 Co18Cr6Pt3Ta 300 1800 13.5
Example 1
Test Cr15Ti3Mo Co13Cr6Pt3Ta 50 2300 C 15
Co40Cr 200 Co18Cr6Pt3Ta 300 2300 15.4
Example 2
Test Cr15Ti3Mo Co13Cr6Pt3Ta 50 2830 C 15
Co40Cr 200 Co18Cr6Pt3Ta 300 2520 15.7
Example 3
Test Cr15Ti3Mo Co13Cr10Pt3Ta 50 4100 C 15
Co40Cr 200 Co18Cr6Pt3Ta 300 2250 14.2
Example 4
Test Cr15Ti3Mo Co13Cr6Pt3Ta 15 540 C 15
Co40Cr 200 Co18Cr6Pt3Ta 300 2010 13.2
Example 5
Test Cr15Ti Co13Cr6Pt3Ta 50 1800 C 15
Co40Cr 200 Co18Cr6Pt3Ta 300 2350 15.8
Example 6
Test Cr15Ti Co13Cr6Pt3Ta 30 1595 C 15
Co40Cr 200 Co18Cr6Pt3Ta 300 2300 16.3
Example 7
Test Cr15Ti3Mo Co13Cr6Pt3Ta 100 2309 C 15
Co40Cr 200 Co18Cr6Pt3Ta 300 2250 13.3
Example 8
Test Cr15Ti3Mo Co13Cr6Pt3Ta 150 2462 C 15
Co40Cr 200 Co18Cr6Pt3Ta 300 2350 12.5
Example 9
Test Cr15Ti3Mo Co13Cr6Pt3Ta 200 2385 C 15
Co40Cr 200 Co18Cr6Pt3Ta 300 2300 11.3
Example 10
Test Cr15Ti3Mo Co13Cr6Pt3Ta 50 1595 C 15
Co40Cr 200 Co18Cr6Pt3Ta 300 726 11.3
Example 11
Test Cr15Ti3Mo Co13Cr6Pt3Ta 50 1595 C 15
Co40Cr 200 Co18Cr6Pt3Ta 300 1726 14.1
Example 12
Test Cr15Ti3Mo Co13Cr6Pt3Ta 50 1595 C 15
Co40Cr 200 Co18Cr6Pt3Ta 300 2362 15.4
Example 13
Test Cr15Ti3Mo Co13Cr6Pt3Ta 50 1595 C 15
Co40Cr 200 Co18Cr6Pt3Ta 50 726 11.5
Example 14
Test Cr15Ti3Mo Co13Cr6Pt3Ta 50 1595 C 15
Co40Cr 200 Co18Cr6Pt3Ta 100 1950 15.0
Example 15
Test Cr15Ti3Mo Co13Cr6Pt3Ta 50 1595 C 15
Co40Cr 200 Co18Cr6PtTa 300 2350 15.4
Example 16
Test Cr15Ti3Mo Co13Cr6Pt3Ta 50 1595 C 15
Co40Cr 200 Co18Cr6Pt3Ta 500 2530 15.6
Example 17
Test Cr15Ti3Mo Co13Cr6Pt3Ta 50 1595 C 15
Co40Cr 200 Co18Cr6Pt3Ta 1000 2400 13.7
Example 18
Test Cr15Ti3Mo Co13Cr6Pt3Ta 50 1595 C 15
Co40Cr 200 Co18Cr6Pt3Ta 1500 2461 13.0
Example 19
Test Cr15Ti3Mo Co13Cr6Pt3Ta 50 1595 -- --
Co40Cr 200 Co18Cr6Pt3Ta 300 440 12.5
Example 20
Test Cr15Ti3Mo Co13Cr6Pt3Ta 50 1595 C 15
-- -- Co18Cr6Pt3Ta 300 1450 13.5
Example 21
Test Cr15Ti3Mo Co13Cr6Pt3Ta 50 1595 -- --
-- -- Co18Cr6Pt3Ta 300 410 12.4
Example 22
It is seen from Table 1 that the magnetic recording media of Test Examples 2 and 3 in which the coercivity Hc of the in-plane magnetic film was from 1,500 to 4,000 Oe exhibited excellent noise properties as compared with the magnetic recording medium of Test Example 4 in which the coercivity Hc exceeded that range.
Furthermore, the recording media of Test Examples 2 and provided a single peak isolated waveform at reproduction, whereas the magnetic recording medium of Test Example 1 in which the coercivity Hc was below the above-described range provided an isolated waveform containing a di-pulse waveform at reproduction but did not form a single peak waveform.
It is also seen that the magnetic recording media of Test Examples 6 to 8 in which the remnant magnetization film thickness product BrT of the in-plane magnetic film 3 was from 20 to 100 G.mu.m exhibited excellent noise properties as compared with the magnetic recording media of Test Examples 9 and 10 in which the BrT exceeded that range. In particular, the magnetic recording media of Test Examples 6 and 7 in which the BrT was from 20 to 50 G.mu.m exhibited more excellent noise properties.
Furthermore, the recording media of Test Examples 6 to 8 provided a single peak solitary waveform at reproduction, whereas the magnetic recording medium of Test Example 5 in which the BrT was below the above-described range provided an isolated waveform containing a di-pulse waveform at reproduction but did not form a single peak waveform.
It is also seen that the magnetic recording media of Test Examples 12 and 13 in which the coercivity of the vertical magnetic film 6 was 1,500 Oe or more exhibited excellent noise properties as compared with the magnetic recording medium of Test Example 11 in which the coercivity Hc was less than 1,500 Oe.
It is also seen that the magnetic recording media of Test Examples 15 to 18 in which the thickness of the vertical magnetic film 6 was from 100 to 1,000 .ANG. exhibited excellent noise properties as compared with the magnetic recording media of Test Examples 14 and 19 in which the thickness of the vertical magnetic film 6 was not within that range. In particular, the magnetic recording media of Test Examples 15 and 16 in which the thickness was from 100 to 600 .ANG. exhibited more excellent noise properties.
It is also seen that the magnetic recording media having a separation film 4 exhibited excellent noise properties as compared with the magnetic recording media of Test Examples 20 and 22 in which a separation film 4 was not formed.
Furthermore, it is seen that the magnetic recording media having a nonmagnetic intermediate layer 5 exhibited excellent noise properties as compared with the magnetic recording media of Test Examples 21 and 22 in which a nonmagnetic intermediate layer 5 was not formed.
Test Example 23
The surface of an aluminum alloy substrate (diameter: 84 mm, thickness: 0.8 mm) having formed on the surface thereof an NiP plating film (thickness: 15 .mu.m) was subjected to mechanical texturing to have a surface average roughness Ra of 15 .ANG.. The resulting substrate 1 was set in a chamber of a DC magnetron sputtering device (3010, manufactured by ANELVA).
The chamber was evacuated until the ultimate vacuum reached 2.times.10.sup.-7 Pa, the substrate 1 was heated to 200.degree. C., and then on the substrate 1, an in-plane magnetic film underlayer 2 (thickness: 200 .ANG.), an in-plane magnetic film 3, a separation film 4, a nonmagnetic intermediate layer 5 comprising Co-40 at % and Cr (Co40Cr) and a vertical magnetic film 6 comprising Co-18 at %, Cr-6 at %, Pt-3 at % and Ta (Co18Cr6Pt3Ta) were sequentially formed by sputtering.
Subsequently, a carbon protective film having a thickness of 100 .ANG. was formed on the vertical magnetic film 6, and then a lubricant was coated on the carbon protective film to form a lubricating film (thickness: 20 .ANG.) comprising PFPE, to thereby obtain a magnetic recording medium.
Test Examples 24 to 39
Magnetic recording media were manufactured in the same manner as in Test Example 23, except for the changes indicated in Table 2 below.
Test Examples 40 and 41
Magnetic recording media were manufactured in the same manner as in Test Example 23, except that a separation film 4 or a nonmagnetic intermediate layer 5 was not formed.
The magnetic recording media of the respective Test Examples were evaluated in the same manner as Test Examples 1 to 22. The results are set forth in Table 2 below.
TABLE 2
Nonmagnetic
In-plane Separation
Intermediate
Magnetic Film
Layer Vertical Magnetic Film Repro-
Film In-plane Magnetic Film Thick-
Thick- Thick- duction
Underlayer BrT Hc Compo- ness
Compo- ness ness Hc Properties
Composition Composition (G.mu.m) (Oe) sition (.ANG.)
sition (.ANG.) Composition (.ANG.) (Oe) SNR (dB)
Test Cr Co17Cr5Ta 50 1800 C 20
Co40Cr 200 Co18Cr6Pt3Ta 500 2550 14.8
Example 23
Test Cr Co17Cr5Ta 50 1800 C 50
Co40Cr 200 Co18Cr6Pt3Ta 500 2670 15.3
Example 24
Test Cr Co17Cr5Ta 50 1800 Ta 50
Co40Cr 200 Co18Cr6Pt3Ta 500 2150 14.3
Example 25
Test Cr Co17Cr5Ta 50 1800 Ta 100
Co40Cr 200 Co18Cr6Pt3Ta 500 2245 14.6
Example 26
Test Cr Co17Cr5Ta 50 1800 NiP 50
Co40Cr 200 Co18Cr6Pt3Ta 500 1950 14.3
Example 27
Test Cr Co17Cr5Ta 50 1800 W 50
Co40Cr 200 Co18Cr6Pt3Ta 500 2315 14.9
Example 28
Test Cr Co17Cr5Ta 50 1800 Re 50
Co40Cr 200 Co18Cr6Pt3Ta 500 2435 15.4
Example 29
Test Cr Co17Cr5Ta 50 1800 CuTi 50
Co40Cr 200 Co18Cr6Pt3Ta 500 2050 14.4
Example 30
Test Cr Co17Cr5Ta 50 1800 SiC 50
Co40Cr 200 Co18Cr6Pt3Ta 500 2250 14.8
Example 31
Test Cr Co17Cr5Ta 50 1800 Ti 50
Co40Cr 200 Co18Cr6Pt3Ta 500 2450 14.7
Example 32
Test Cr Co17Cr5Ta 50 1800 Zr 50
Co40Cr 200 Co18Cr6Pt3Ta 500 2350 15.0
Example 33
Test Cr Co17Cr5Ta 50 1800 C 2
Co40Cr 200 Co18Cr6Pt3Ta 500 780 11.0
Example 34
Test Cr Co17Cr5Ta 50 1800 W 300
Co40Cr 400 Co18Cr6Pt3Ta 500 2350 13.9
Example 35
Test Cr15Ti3Mo Co18Cr5Pt2Ta2Zr 50 2200 C 20
Co40Cr 200 Co18Cr6Pt3Ta 500 2720 15.9
Example 36
Test Cr15W Co20Cr8Pt2Ta3Zr 50 2000 C 20
Co40Cr 200 Co18Cr6Pt3Ta 500 2820 16.1
Example 37
Test Cr15V Co17Cr8Pt3Ta 50 1900 C 20
Co40Cr 200 Co18Cr6Pt3Ta 500 2650 15.4
Example 38
Test Cr4Ti Co19Cr6Pt2Ta2Re 50 2000 C 20
Co40Cr 200 Co18Cr6Pt3Ta 500 2520 15.6
Example 39
Test Cr Co17Cr5Ta 50 1800 -- --
Co40Cr 200 Co18Cr6Pt3Ta 500 435 10.3
Example 40
Test Cr Co17Cr5Ta 50 1800 C 20
-- -- Co18Cr6Pt3Ta 500 1850 12.6
Example 41
It is seen from Table 2 that the magnetic recording media in which a separation film 4 comprising Ta, Re, CuTi, SiC, W, NiP, Zr, Ti or C was formed exhibited excellent noise properties.
Furthermore, the recording medium of Test Example 34 in which the thickness of the separation film 4 was 2 .ANG. formed an isolated waveform slightly containing a di-pulse waveform at reproduction, however, the magnetic recording media of the other Test Examples provided a single peak isolated waveform.
Test Example 42
The surface of an aluminum alloy substrate (diameter: 84 mm, thickness: 0.8 mm) having formed on the surface thereof an NiP plating film (thickness: 15 .mu.m) was subjected to mechanical texturing to have a surface average roughness Ra of 15 .ANG.. The resulting substrate 1 was set in a chamber of a DC magnetron sputtering device (3010, manufactured by ANELVA).
The chamber was evacuated until the ultimate vacuum reached 2.times.10.sup.-7 Pa, the substrate 1 was heated to 200.degree. C. and then on the substrate 1, an in-plane magnetic film underlayer 2 (thickness: 200 .ANG.) comprising Cr, an in-plane magnetic film 3 comprising Co-17 at %, Cr-5 at % and Ta (Co17Cr5Ta), a separation film 4 comprising carbon, a nonmagnetic intermediate layer 5 comprising Co-40 at % and Cr (Co40Cr) and a vertical magnetic film 6 comprising Co-18 at %, Cr-6 at %, Pt-3 at % and Ta (Co18Cr6Pt3Ta) were sequentially formed by sputtering.
Subsequently, a carbon protective film having a thickness of 100 .ANG. was formed on the vertical magnetic film 6. A lubricant was then coated on the carbon protective film to form a lubricating film (thickness: 20 .ANG.) comprising PFPE, to thereby obtain a magnetic recording medium.
Test Examples 43 to 50
Magnetic recording media were manufactured in the same manner as Test Example 42, except for changing the constituent material of the nonmagnetic intermediate layer 5 as shown in Table 3.
Test Examples 51 to 59
Magnetic recording media were manufactured by varying the constituent material of the vertical magnetic film 6 as shown in Table 4.
Test Examples 60 to 63
Magnetic recording media were manufactured by varying the thickness of the nonmagnetic intermediate layer 5 as shown in Table 5.
The magnetic recording media of the respective Test Examples were evaluated in the same manner as Test Example 1 to 42. The results are set forth in Tables 3 to 5 below.
TABLE 3
Nonmagnetic Repro-
In-plane Separation
Intermediate duction
Magnetic Film
Layer Vertical Magnetic Film Prop-
Film In-plane Magnetic Film Thick-
Thick- Thick- erties
Underlayer BrT Hc Compo- ness
ness ness Hc SNR
Composition Composition (G.mu.m) (Oe) sition (.ANG.)
Composition (.ANG.) Composition (.ANG.) (Oe) (dB)
Test Cr Co17Cr5Ta 50 2015 C 25 Co40Cr
200 Co18Cr6Pt3Ta 300 2580 13.5
Example
42
Test Cr Co17Cr5Ta 50 2015 C 25
Co25Cr10Pt3Ta 200 Co18Cr6Pt3Ta 300 2730 14.3
Example
43
Test Cr Co17Cr5Ta 50 2015 C 25
Co30Cr8Pt3Zr 200 Co18Cr6Pt3Ta 300 2690 14.0
Example
44
Test Cr Co17Cr5Ta 50 2015 C 25
Co35Cr5Pt3Ta2Cu 200 Co18Cr6Pt3Ta 300 2815 14.9
Example
45
Test Cr Co17Cr5Ta 50 2015 C 25
Co35Cr5Pt2Ta2Re 200 Co18Cr6Pt3Ta 300 2735 15.6
Example
46
Test Cr Co17Cr5Ta 50 2015 C 25
Co40Cr3Pt2Re 200 Co18Cr6Pt3Ta 300 2645 14.1
Example
47
Test Cr Co17Cr5Ta 50 2015 C 25
Co65Cr5Ta 200 Co18Cr6Pt3Ta 300 1500 12.1
Example
48
Test Cr Co17Cr5Ta 50 2015 C 25
Co10Cr2Pt 200 Co18Cr6Pt3Ta 300 2200 10.5
Example
49
Test Cr Co17Cr5Ta 50 2015 C 25
Co60Cr20Pt15Ta 200 Co18Cr6Pt3Ta 300 1750 11.8
Example
50
TABLE 4
Nonmagnetic
In-plane Separation
Intermediate
Magnetic Film
Layer Vertical Magnetic Film Repro-
Film In-plane Magnetic Film Thick-
Thick- Thick- duction
Underlayer BrT Hc Compo- ness Compo-
ness ness Hc Properties
Composition Composition (G.mu.m) (Oe) sition (.ANG.) sition
(.ANG.) Composition (.ANG.) (Oe) SNR (dB)
Test Cr Co17Cr5Ta 50 2015 C 15 Co40Cr
200 Co20Cr8Pt4Ta 300 2195 15.2
Example 51
Test Cr Co17Cr5Ta 50 2015 C 15 Co40Cr
200 Co25Cr10Pt2Ta 400 1760 15.3
Example 52
Test Cr Co17Cr5Ta 50 2015 C 15 Co40Cr
200 Co22Cr9Pt3Zr 400 1895 15.1
Example 53
Test Cr Co17Cr5Ta 50 2015 C 15 Co40Cr
200 Co18Cr5Pt4Ta2Zr 300 2850 15.6
Example 54
Test Cr Co17Cr5Ta 50 2015 C 15 Co40Cr
200 Co22Cr10Pt2Ta2Zr 500 1975 16.1
Example 55
Test Cr Co17Cr5Ta 50 2015 C 15 Co40Cr
200 Co38Cr6Pt3Ta 300 525 10.1
Example 56
Test Cr Co17Cr5Ta 50 2015 C 15 Co40Cr
200 Co35Cr16Pt5Ta 300 610 9.5
Example 57
Test Cr Co17Cr5Ta 50 2015 C 15 Co40Cr
200 Co30Cr10Pt15Zr 300 725 10.3
Example 58
Test Cr Co17Cr5Ta 50 2015 C 15 Co40Cr
200 Co30Cr5Pt15Ta 300 253 8.1
Example 59
TABLE 5
Nonmagnetic Repro-
In-plane Separation
Intermediate duction
Magnetic Film Layer
Vertical Magnetic Film Prop-
Film In-plane Magnetic Film Thick-
Thick- Thick- erties
Underlayer BrT Hc Compo- ness
ness ness Hc SNR
Composition Composition (G.mu.m) (Oe) sition (.ANG.)
Composition (.ANG.) Composition (.ANG.) (Oe) (dB)
Test Cr Co17Cr5Ta 50 2015 C 15
Co35Cr8Pt3Ta 15 Co19Cr6Pt3Ta2Zr 300 870 9.5
Example
60
Test Cr Co17Cr5Ta 50 2015 C 15
Co35Cr8Pt3Ta 100 Co19Cr6Pt3Ta2Zr 300 1980 14.3
Example
61
Test Cr Co17Cr5Ta 50 2015 C 15
Co35Cr8Pt3Ta 200 Co19Cr6Pt3Ta2Zr 300 2310 15.2
Example
62
Test Cr Co17Cr5Ta 50 2015 C 15
Co35Cr8Pt3Ta 600 Co19Cr6Pt3Ta2Zr 300 2200 13.1
Example
63
It is seen from Tables 3 to 5 that the magnetic recording media in which the nonmagnetic intermediate layer 5 was formed from a Co alloy consisting of from 25 to 50 at % of Cr, from 0 to 15 at % of Pt, from 0 to 10 at % of one or more of Ta, Zr, Cu and Re and the balance of Co and the vertical magnetic film 6 was formed from a Co alloy consisting of from 16 to 30 at % of Cr, from 0 to 15 at % of Pt, from 2 to 10 at % of Ta, from 0 to 5 at % of Zr and the balance of Co exhibited excellent noise properties as compared with the magnetic recording media in which the component ratio in the nonmagnetic intermediate layer 5 or the vertical magnetic film was not within the above-described range. Also, the magnetic recording media formed a satisfactory single peak signal waveform.
Furthermore, the recording media in which the thickness of the nonmagnetic intermediate layer 5 was from 20 to 200 .ANG. and the clearance between the in-plane magnetic film 3 and the vertical magnetic film 6 was from 10 to 500 .ANG. exhibited excellent noise properties and formed a complete single peak isolated waveform at reproduction. On the other hand, the magnetic recording media in which the thickness of the nonmagnetic intermediate layer 5 and the clearance between the in-plane magnetic film 3 and the vertical magnetic film 6 were not within the above-described range had a slightly reduced coercivity or the single peak tendency of the signal wave was slightly reduced.
As describe in the foregoing, the recording medium of the present invention enables application of a signal processing system used in the reproduction of general-purpose in-plane magnetic recording media and ensures excellent noise properties.
While the invention has been described in detail and with reference to specific embodiment thereof, it will be apparent to one skilled in the art that various changes and modifications can made therein without departing from the spirit and scope
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