Patent Application
20060051620
This application claims priority from Japanese Patent Application No. JP2004-262853, filed Sep. 9, 2004, the entire disclosure of which is incorporated herein by reference.
The present invention relates to a magnetic recording apparatus capable of recording large capacity information and, particularly, it relates to a magnetic recording medium suitable for high density magnetic recording and a manufacturing method thereof.
For magnetic storage apparatus typically represented by a magnetic disk drive, a demand for larger capacity has increased more and more. To satisfy the demand, development for magnetic heads with high sensitivity and magnetic recording media capable of obtaining a high signal amplitude to noise ratio (S/Nd) has been demanded.
Generally, a recording medium comprises a first underlayer referred to as a seed layer, a second underlayer whose structure is body centered cubic comprising a chromium alloy, a magnetic layer, a protective layer mainly comprising carbon and a lubricant layer mainly comprising perfluoro alkyl polyether, which are formed on a substrate. For the magnetic layer, a cobalt-based alloy whose structure is hexagonal close-packed is used.
To improve S/Nd, it is effective that c-axis of the magnetic layer having hexagonal close-packed structure, which is an easy axis of the magnetization, is directed to in-plane direction by making (11.0) plane or (10.0) plane of the magnetic layer parallel to the surface of the substrate. It has been known that the crystal orientation of the magnetic layer can be controlled by a seed layer and such orientation can be obtained by using, for example, tantalum or an NiAl alloy having B2 structure as the seed layer. Further, it has been known that the magnetic property in the circumferential direction can be improved also by introducing magnetic anisotropy in the circumferential direction by applying mechanical texturing to the surface of the substrate.
To improve S/Nd, it is effective to take a multi-layered structure for the magnetic layer, refine the crystal grain size, and decrease Br·t which is a product of the residual magnetic flux density (Br) and the film thickness of the magnetic layer. That is, a magnetic recording medium has been proposed which is formed on a substrate by depositing underlayers, and magnetic layers which have at least two layers separated by way of non-magnetic layers such as ruthenium. In addition, a magnetic recording medium has been proposed which is formed on a substrate by depositing underlayers and magnetic layers in this order, and the magnetic recording layers are separated vertically by intermediate layers, the interlayers comprise one of materials selected from Ru, Rh, Ir and alloys thereof, the thickness of the intermediate layers is from 0.2 to 0.4 nm or from 1.0 to 1.7 nm, and the magnetization of the magnetic recording layers separated by the intermediate layers is in parallel with each other. Such magnetic recording media described above realize low noise and enough thermal stability to maintain the magnetic property.
Reduction of noise is limited since the thermal stability is deteriorated when the grain size of the magnetic recording layer is refined extremely, or Br·t is greatly decreased. In recent years, an anti-ferromagnetically coupled (AFC) medium has been proposed as a technique compatibilizing the thermal stability and low noise. AFC medium has two magnetic layers which are anti-ferromagnetically coupled by way of Ru intermediate layer. This structure can make Br·t lower while the magnetic film is kept thicker compared with the medium comprising a single magnetic layer. Accordingly, reduction of the medium noise has become possible while the thermal stability is maintained.
Patent Document 1 (US Patent Publication No. 2002/98390A1) discloses a longitudinal magnetic recording medium stacked on a substrate in which a magnetic recording layer comprises an AFC layer and a single ferromagnetic layer spaced apart by a non-ferromagnetic spacer layer. The AFC layer is formed as two ferromagnetic films antiferromagnetically coupled together across an antiferromagnetically coupling film that has a composition and thickness to induce antiferromagnetic coupling. In each of the two remanent magnetic states, the magnetic moment of the two antiferromagnetically coupled films in the AFC layer are oriented antiparallel, and the magnetic moment of the single ferromagnetic layer and the greater-moment ferromagnetic film of the AFC layer are oriented parallel. The non-ferromagnetic spacer layer has a composition and thickness to prevent antiferromagnetic exchange coupling. Further, it discloses a medium in which Co-12 at. % Pt-14 at. % Cr-11 at. % B alloy is used as the greater-moment magnetic film of the AFC layer and the single ferromagnetic layer in column No. 51.
Even when the techniques described above are combined, however, this is still insufficient to attain an areal recording density of 150 Mbit per mm2 or more and it is necessary to further improve the signal amplitude and improve S/Nd.
A feature of the present invention is to provide a longitudinal magnetic recording medium having high S/Nd, enough overwrite-characteristics and sufficient stability against thermal fluctuation.
An exemplary embodiment of the invention disclosed in the present patent application will be described as below. A magnetic recording medium is provided in which an underlayer, a first magnetic layer, a first intermediate layer, a second magnetic layer, a second intermediate layer, a third magnetic layer, a protective layer, and a lubricant layer are formed successively on a substrate. The second magnetic layer and the third magnetic layer each comprise a cobalt (Co)-based alloy containing platinum (Pt), chromium (Cr), and boron (B). The concentration of chromium contained in the third magnetic layer is less than that in the second magnetic layer. The concentration of chromium contained in the third magnetic layer is about 15 at. % or less.
Further, a magnetic disk apparatus is provided which includes a combination of a medium having the constitution described above and a magnetic head in which the ratio of a writing gap length and a geometrical writing track width is from about 1.5 to 2.1.
The invention can provide a longitudinal magnetic recording medium having a high S/Nd, enough overwrite-characteristics and sufficient stability against thermal fluctuation. Further, it can provide a magnetic recording apparatus whose areal recording density is 150 Mbit/mm2 or more.
As the substrate, a glass substrate, an aluminum-magnesium (Al—Mg) alloy substrate coated with a nickel-phosphorus (Ni—P) plating film, or a ceramic substrate is used. It is preferred to use a substrate applied at the surface thereof with texturing and form a magnetic layer and a protective layer by way of an underlayer on the substrate. When a substrate in which concentrical grooves are formed on the surface by texturing is used, since Br·t measured in the circumferential direction is larger than Br·t measured in the radial direction, the thickness of the magnetic layer can be reduced to enhance the signal amplitude resolution. While the texturing may be applied after formation of the underlayer, it is preferred to apply texturing directly to the surface of the substrate, and then form thin films continuously after cleaning and drying.
The underlayers (11, 12, 13) have a first underlayer (11) comprising a titanium (Ti) alloy containing at least one element selected from cobalt (Co) and nickel (Ni), a second underlayer (12) comprising a tungsten (W) alloy containing cobalt (Co), and a third underlayer (13) comprising a chromium (Cr) alloy containing titanium (Ti) and boron (B) formed in this order. The titanium alloy layer containing at least one element selected from cobalt and nickel, the tungsten alloy layer containing cobalt, and the Cr alloy layer containing Ti and B are preferably used as the underlayer to be formed on the substrate. This is because the magnetic layer formed on the underlayer can be easily given in-plane orientation magnetically and the crystal grain size of the magnetic layer can be refined to reduce the medium noise. Further, when the surface of the tungsten alloy layer containing cobalt is oxidized intentionally in an oxygen atmosphere or in a mixed gas atmosphere of Ar with addition of oxygen after formation of the tungsten alloy layer containing cobalt, (100) orientation of the Cr alloy underlayer can be improved further. Since use of alloy layer having an amorphous structure instead of the titanium alloy layers containing at least one element selected from cobalt and nickel and the tungsten alloy layer containing cobalt can provide a similar or identical effect, there is no particular restriction. The amorphous structure of the alloy layers was identified based on the fact that it showed no distinct diffraction peak other than the hallo pattern in an X-ray diffraction curve using Cu Kα1 X-ray, or based on the fact that the average grain size obtained from lattice images photographed by a high resolution electron microscope was 5 nm or less. When an alloy layer having a body centered cubic structure comprising Cr as a main ingredient is formed on the amorphous alloy layers, the Cr alloy layer can be oriented in (100) plane.
The magnetic layer formed on the Cr alloy layer containing Ti and B is preferred since the crystal grains are refined to reduce the medium noise. Instead of the Cr alloy, it is also possible to use a Cr alloy containing at least one element selected from Ti, molybdenum (Mo), and W, or an alloy having a body centered cubic structure comprising Cr as a main ingredient. Alternatively, a multi-layered structure comprising the alloy layers such as (Cr—Mo)/(Cr—Ti) may also be used.
The first magnetic layer (14) is a Co-based alloy. The film thickness is preferably reduced to such an extent as capable of anti-ferromagnetically coupling, although it depends on the composition of the magnetic film. It is preferred that the first magnetic layer is a Co-based alloy containing Cr or a Co-based alloy containing Cr and Pt to give easily in-plane orientation magnetically on the underlayer.
The first intermediate layer (15) for attaining the anti-ferromagnetical exchange coupling between the first and second magnetic layers (14, 16) comprises ruthenium (Ru) as a main ingredient. When a layer comprising Ru as the main ingredient at a thickness of 1.5 nm or less is formed by using a sputtering target containing Ru, the layer sometimes contains the constituent elements in the upper and lower layers. For the first intermediate layer, an alloy comprising at least one element selected from Ru, iridium (Ir) and rhodium (Rh) or the elements described above as the main ingredient can be used, for instance. The thickness is preferably from 0.5 to 0.8 nm since the first magnetic layer and the second magnetic layer tend to be anti-ferromagnetically coupled with each other to give less thermal fluctuation. The first magnetic layer and the first intermediate layer are preferred to give small Br t with enough coercivity even when the thickness of the second magnetic layer is thicker compared with the case of not forming the first magnetic layer and the first intermediate layer.
Each of the second magnetic layer (16) and the third magnetic layer (18) is a Co-based alloy containing Pt, Cr and B. This is because Pt is essential to increase the coercivity, and Cr and B are essential to reduce the medium noise. Further, the concentration of chromium contained in the third magnetic layer is less than that in the second magnetic layer, and the concentration of chromium contained in the third magnetic layer is 15 at. % or less.
The second intermediate layer (17) disposed between the second and third magnetic layers (16, 18) to attain anti-ferromagnetical coupling between both the layers contains Ru. The protective layer (19) comprises carbon as a main ingredient and the lubricant layer (20) comprises a perfluoro alkyl polyether as a main ingredient.
At first, to achieve a high areal recording density, a structure of a head optimal to this medium has been studied. The medium used as specimens was manufactured as described below. An alumino silicate glass substrate 10 chemically strengthened at the surface was put to alkali cleaning and drying, then an argon (Ar) gas was introduced in a vacuum, and a 15 nm-thick Ti-40 at. % Co-10 at. % Ni alloy layer as a first underlayer 11 and a 3 nm-thick W-30 at. % Co alloy layer as a second underlayer 12 were formed on the substrate by a sputtering method at room temperature. Then, after heating the substrate by using a lamp heater, a 10 nm-thick Cr-10 at. % Ti-3 at. % B alloy layer as a third underlayer 13 was formed. Further, a 3 nm-thick first magnetic layer 14 comprising a Co-16 at. % Cr-9 at. % Pt alloy layer, a 0.6 nm-thick first intermediate layer 15 comprising Ru, a second magnetic layer 16 comprising a Co-16 at. % Cr-12 at. % Pt-8 at. % B alloy, a 0.8 nm-thick second intermediate layer comprising Ru, and a third magnetic layer 18 comprising a Co-14 at. % Cr-14 at. % Pt-8 at. % B alloy were formed in sequence, and a 3 nm-thick carbon film 19 was formed as a protective layer.
After formation of the carbon film, a 1.8 nm-thick lubricant layer 20 comprising perfluoro alkyl polyether as a main ingredient was coated. The multi-layered film described above was formed by using a single-wafer sputtering apparatus (MDP250B) manufactured by Intevac Corp. The base vacuum pressure of the sputtering apparatus was 1.0 to 1.2×10−5 Pa, and the tact time was set to 7 sec. From the first underlayer to the third magnetic layer were formed in Ar gas atmosphere at 0.93 Pa, and the carbon protective film was formed in a mixed gas atmosphere comprising Ar with addition of 10% nitrogen. The substrate was heated in a mixed gas atmosphere comprising Ar with addition of 1% oxygen, and the heating temperature was controlled such that the coercivity of the manufactured magnetic recording medium was within a range from 300 to 320 kA/m.
The magnetic properties and the R/W performance of the manufactured magnetic recording medium were evaluated by the following method. The magnetic properties were evaluated by using vibrating sample magnetometer (VSM) while applying 796 kA/m at the maximum in the circumferential direction at room temperature. The R/W performance was evaluated by a spin stand having a combination of an electromagnetic inductive writing head and a spin valve type reading magnetic head. The writing gap length (GI) was 100 nm, the inter-shield gap length (Gs) was 56 nm, and the geometrical reading track width (Twr) was 100 nm, and the geometrical writing track width (Tww) was 180 nm for the head used for the evaluation of the R/W performance. After writing at a signal at 5.31 kFC/mm (135 kFCI) as an 1F signal for low recording density, a signal at 31.9 kFC/mm (810 kFCI) as a 2F signal for high recording density were overwritten to determine an overwrite characteristic (O/W) based on the decay ratio of the 1F signal. S/Nd was defined as: S/Nd=20 log (So/Nd2F) by using the medium noise (Nd2F) at the high recording density which is 34.9 kFC/mm and the isolated pulse signal amplitude (So).
Assuming the film thickness and the residual magnetic flux density of the first magnetic layer as t1 and Br1, respectively, the film thickness and the residual magnetic flux density of the second magnetic layer as t2 and Br2, respectively, and the film thickness and the residual magnetic flux density of the third magnetic layer as t3 and Br3, respectively, Br·t in this example is about: Br t=Br3—t3+Br2−t2−Br1·t1. When the thickness of each of the second and the third magnetic layers was changed such that Br·t was substantially equal by using the magnetic alloy target described above, the absolute value of O/W was maximized and the signal decay due to thermal fluctuation was improved under the condition where the thickness of each of the layers was: about Br3·t3=Br2−t2−Br1−t1.
The magnetic recording medium whose Br·t was in a range from 4T·nm to 10T·nm by controlling the thicknesses of the second and third magnetic layers was formed such that substantially Br3·t3=Br2−t2−Br1·t1 by using the magnetic alloy target described above. In this case, the absolute value of O/W was decreased monotonously along with increase of Br·t. This tendency of O/W did not depend on the film composition of the magnetic layers. Br·t and O/W had a relation as: O/W=−35 dB at Br·t=6T·nm and O/W=−27 dB at Br·t=10T·nm. The signal decay due to thermal fluctuation was improved along with increase of Br·t. In the medium described in this example, the signal decay was about from −1.4%/decade to 1.5%/decade so long as Br·t was 7.5 T·nm or more, which was sufficiently stable against thermal fluctuation and had no problem from the view point of the reliability. The thermal decay at 65° C. was evaluated by the decay rate of the signal amplitude when the medium was left for 1 sec to 1000 sec after recording. The R/W performance was evaluated by using heads with changing the writing gap length (Gl), the inter-shield gap length (Gs), geometrical reading track width (Twr), and the geometrical writing track width (Tww) at a low recording density as IF signal which is 5.31 kFC/mm (135 kFCI) and at a high density recording as 2F signal which is 31.9 kFC/mm (810 kFCI). While O/W was somewhat deteriorated in the head with increased writing gap length (Gl) (specimen No. (SAMPLE #)003), it was within an allowable range. S/Nd was somewhat deteriorated in the head with increased inter-shield gap length (Gs) (specimen No. (SAMPLE #)005), but it was within an allowable range. S/Nd was somewhat deteriorated in the head with increased geometrical reading track width (Twr)(specimen No. (SAMPLE #)006), but it was within an allowable range. O/W was somewhat deteriorated in the head with increased geometrical reading track width (Twr)(specimen No. (SAMPLE #)008), but it was within an allowable range.
Films were formed directly on a glass substrate by using the three kinds of targets described above, and the compositions of the films were analyzed by inductively coupled plasma spectroscopy (ICPS). As a result, the compositions of the targets are almost the same as the compositions of the films.
The specimen in which only the first underlayer was formed and the second and subsequent layers were not formed showed no distinct diffraction peak other than the hallo pattern on the X-ray diffraction curve using Cu Kα1 X-ray. An X-ray diffraction curve for a specimen in which the layers were formed as far as the protective film showed no distinct diffraction peak except for 200 diffraction peak attributable to the third underlayer having a body centered cubic structure, and 11.0 diffraction peak attributable to the first magnetic layer, the second magnetic layer and the third magnetic layer having the hexagonal close-packed structure.
A magnetic recording medium was formed in the same manner as the magnetic recording media described in Example 1 except for using a Co-16 at. % Cr-14 at. % Pt-8 at. % B alloy for the third magnetic layer.
That is, after an alumina silicate glass substrate 10 chemically strengthened at the surface was alkali cleaned and dried, an argon gas was introduced in a vacuum, and a 15 nm-thick Ti-40 at. % Co-10 at. % Ni alloy layer as the first underlayer 11 and a 3 nm-thick W-30 at. % Co alloy layer as the second underlayer 12 were formed on the substrate by a sputtering method at room temperature. Then, the substrate was heated by a lamp heater and a 10 nm-thick Cr-10 at. % Ti-3 at. % B alloy layer as the third underlayer 13, a 3 nm-thick first magnetic layer 14 comprising a Co-16 at. % Cr-9 at. % Pt alloy, a 0.6 nm-thick first intermediate layer 15 comprising Ru, a second magnetic layer 16 comprising a Co-16 at. % Cr-12 at. % Pt-8 at. % B alloy, a 0.8 nm-thick second intermediate layer 17 comprising Ru, and a third magnetic layer 18 comprising a Co-16 at. % Cr-14 at. % Pt-8 at. % B alloy were formed in sequence, and a 3.0 nm-thick carbon film 19 was formed as a protective layer.
The thicknesses of the second and third magnetic layers were controlled such that Br3·t3=Br2−t2−Br1·t1 at about Br·t=8 T·nm.
In this case, Ku·v/kT (Ku: crystal magnetic anisotropy constant, v: volume of a magnetic crystal grain, k: Boltzmann's constant, T: absolute temperature) was determined by fitting the time dependence of the remanence coercivity from 7.5 to 240 sec at room temperature to Sharrock's formula. From the studies made by the present inventors, the signal decay caused by thermal fluctuation could be suppressed enough to result in no problem in view of the reliability when Ku·v/kT determined by the method described above was about 71 or more. All the media in this example had Ku·v/kT of 71 or more, with no problem of reliability against thermal fluctuation.
In view of
In view of
That is, in a case where the geometrical writing track width, etc. of the head were relatively small, better S/Nd was obtained when the Cr concentration of the third magnetic layer was 14 at. % and, on the other hand, in a case where the geometrical writing track width of the head, etc. were relatively large, better S/Nd was obtained when the Cr concentration of the third magnetic layer was 16 at. %.
The phenomena described above can be explained as below. Since magnetization of the third magnetic layer increases by decreasing the Cr concentration in the third magnetic layer from 16 at. % to 14 at. %, the thickness of the third magnetic layer can be reduced when the medium is formed so that Br·t is generally equal. Accordingly, in a case of using a head with a small geometrical writing track width having a relatively low writing performance, good O/W and good S/Nd could be obtained on a medium using the Co-14 at. % Cr-14 at. % Pt-8 at. % B for the third magnetic layer of a smaller thickness (specimen No. (SAMPLE #)101). On the other hand, for a medium using Co-16. at. % Cr-14 at. % Pt-8 at. % B for the third magnetic layer which has a larger thickness, since enough O/W could not be obtained and a substantial writing width was decreased, S/Nd was deteriorated because of reading the track edge noise.
On the contrary, in a case of using a head with a large writing track width having relatively high writing performance, sufficient O/W can be obtained even on the medium using Co-16. at. % Cr-14 at. % Pt-8 at. % B for the third magnetic layer which has larger thickness (sample No. (SAMPLE #)102). In this case, the medium noise was decreased more and higher S/Nd could be obtained because higher concentration of Cr is effective to reduction of the medium noise.
Accordingly, an intended recording density can be obtained by the combination of the medium described above and a magnetic head having the ratio (Tww/Gl) of the writing gap length to the geometrical writing track width being about 1.5 to 2.1. Specifically, a particularly excellent recording density can be attained by combining the medium to be described below and a magnetic head constituting the magnetic recording apparatus having a magnetic head whose writing gap length was about 115 nm or less, inter-shield gap length was about 64 nm or less, geometrical reading track width was about 122 nm or less and geometrical writing track width was about 206 nm or less.
Then, to demonstrate the effect of the Cr concentration in the second magnetic layer (16) and the third magnetic layer (18) on the R/W performance, media whose content of the second and third magnetic layers was changed were formed in the same manner described above. As the materials for use in the second magnetic layer 16 comprising Co as the main ingredient, the following three kinds of alloy targets were used:
Magnetic recording media were formed by controlling the film thickness of the second and the third magnetic layers so that Br3·t3=Br2·t2−Br1·t1 at about Br·t=8 T·nm.
In view of
It is preferred that the concentration of chromium contained in the third magnetic layer is less than that in the second magnetic layer and that the concentration of chromium contained in the third magnetic layer is about 15 at. % or less. This is because reduction of the medium noise, i.e., higher S/Nd and overwrite characteristics are compatible. Elements such as Cr and B are added for refining the crystal grain size of the magnetic film to attain high S/Nd while keeping the thermal stability, and S/Nd can be improved while keeping good overwrite characteristic when the concentration of chromium contained in the third magnetic layer is less than that in the second magnetic layer. When the concentration of Cr contained in the third magnetic layer is higher than about 15 at. %, the magnetic layer becomes excessively thick in order to keep the thermal stability. As a result, the overwrite characteristic is deteriorated and the medium noise increase. Further, when the concentration of Cr contained in the third magnetic layer is higher than that in the second magnetic layer, the exchange interaction between crystal grains in the second magnetic layer becomes stronger than the exchange interaction between the crystal grains in the third magnetic layer. As the exchange interaction between the crystal grains becomes stronger, higher writing field is required for magnetization reversal. Therefore, when the writing field in the second magnetic layer whose exchange interaction between the crystal grains was relatively small, noise due to the second magnetic layer increases and also noise of the entire medium increases.
As has been described above, when the concentration of Cr in the third magnetic layer is about 15 at. % or less and the concentration of Cr in the third magnetic layer is less than that in the second magnetic layer, a magnetic recording medium having an adequate S/Nd to attain an areal recording density of 150 or more Mbit per mm2, and enough O/W characteristic and sufficient stability against thermal fluctuation can be obtained.
The concentration of cobalt (Co) and platinum (Pt) contained in the third magnetic layer (18) was studied in view of S/Nd, overwrite characteristic and thermal stability. In the study, the following alloy targets whose Pt content was fixed and ratio of Co, Cr, and B was changed were used for the third magnetic layer 18 comprising Co as the main ingredient, and magnetic recording media were formed by using the same manufacturing method as described in Example 1.
Magnetic recording media were formed by controlling the film thickness of the second and third magnetic layers so that Br3·t3=Br2·t2−Br1−t1 at about Br·t=8T·nm.
In view of
As has been described above, when the total content of Co and Pt in the third magnetic layer is about 74 at. % or more and about 80 at. % or less, a magnetic recording medium having an adequate S/Nd to attain an areal recording density of 150 or more Mbit per mm2, an excellent O/W characteristic and sufficient stability against thermal fluctuation can be obtained.
The concentration of chromium (Cr) in the third magnetic layer (18) was studied in view of S/Nd, an overwrite characteristic and thermal stability. Magnetic recording media were formed in the same manner as described in Example 1 except for changing the composition of the third magnetic layer. The following seven alloy targets were used for the third magnetic layer.
Magnetic recording media were formed by controlling the film thicknesses of the second and third magnetic layers so that Br3·t3=Br2·t2−Br1·t1 at about Br·t=8 T·nm.
Ku·v/kT of 71 or more and the good absolute value of O/W which was 30 dB or more were obtained on all the specimens in
As has been described above, a magnetic recording medium having an adequate S/Nd to attain an areal recording density of 150 or more Mbit per mm2, an excellent O/W characteristic and sufficient stability against thermal fluctuation can be obtained.
The concentration of Boron (B) in the third magnetic layer (18) was studied in view of S/Nd, an overwrite characteristic and thermal stability. Magnetic recording media were formed in the same manner as described in Example 1 except for changing the composition of the third magnetic layer. The following seven alloy targets were used for the third magnetic layer.
The magnetic recording media were formed by controlling the film thicknesses of the second and third magnetic layers so that Br3·t3=Br2·t2−Br1·t1 at about Br·t=8 T·nm.
It is difficult to add B with high concentration in excess of about 16 at. % to the third magnetic layer due to the problem with the workability of the target. When an alloy containing B at a concentration exceeding about 16 at. % is to be fabricated into a target after vacuum melting, it is difficult to be fabricated as the target because the target tends to be cracked.
From the results described above, B added to the third magnetic layer is preferably about 7 at. % or more for reducing the medium noise. Further, it is preferably about 16 at. % or less in view of the target fabrication. As has been described above, a magnetic recording medium having an adequate S/Nd to attain an areal recording density of 150 or more Mbit per mm2, an excellent O/W characteristic and sufficient stability against thermal fluctuation can be obtained.
The concentration of platinum (Pt) in the third magnetic layer (18) was studied from the view point of S/Nd, an overwrite characteristic and thermal stability. In the study, R/W performance of media whose Pt concentration of the third magnetic layer (MAGLAY3) was changed was measured. Magnetic recording media were formed in the same manner as described in Example 1 except for changing the composition of the third magnetic layer. The following five alloy targets were used for the third magnetic layer.
Magnetic recording media were formed by controlling the film thicknesses of the second and third magnetic layers so that Br3·t3=Br2·t2−Br1·t1 at about Br·t=8 T·nm.
Ku·v/kT of 71 or more was obtained in all the media in
Accordingly, it is preferred that the concentration of Pt contained in the third magnetic layer is about 15 at. % or less. This is because the overwrite characteristic tends to be deteriorated by the increase of the anisotropic magnetic field in the magnetic film as the Pt concentration is higher than that described above.
As has been described above, when the concentration of Pt in the third magnetic layer is about 15 at. % or less, a magnetic recording medium having an adequate S/Nd to attain an areal recording density of 150 or more Mbit per mm2, an excellent O/W characteristic and sufficient stability against thermal fluctuation can be obtained.
The effect of adding tantalum (Ta) to the third magnetic layer (18) was studied from the view point of S/Nd, an overwrite characteristic and thermal stability. In the study, R/W performance of media whose Ta concentration in the third magnetic layer (MAGLAY3) was changed was measured. Magnetic recording media were formed in the same manner as described in Example 1 except for changing the composition of the third magnetic layer. The following six alloy targets were used for the third magnetic layer.
Magnetic recording media were formed by controlling the film thicknesses of the second and third magnetic layers so that Br3·t3=Br2·t2−Br1·t1 at about Br·t=8 T·nm.
As shown in
As the results of the study described above, to ensure the overwrite characteristic, the concentration of Ta added to the third magnetic layer is preferably about 4 at. % or lower. Further, the concentration of Ta added to the third magnetic layer is preferably about 1 at. % or higher since the thermal stability is improved. This can be explained as below. When Ta is added to the Co-based alloy containing Pt, Cr and B, the melting point is lowered. This leads to the effect of decreasing the stacking faults during film growth in the sputtering and result in the improvement of the thermal stability. However, since magnetization of the magnetic layer decreases when the concentration of Ta added to the third magnetic layer is excessive, the film thickness increases for ensuring a constant Br·t and the overwrite characteristic is deteriorated.
As described above, a magnetic recording medium having an adequate S/Nd to attain an areal recording density of 150 or more Mbit per 1 m2, an excellent O/W characteristic and higher thermal stability can be obtained. Further, application of a bias voltage from −100 to −400 V to the substrate during the film formation of the third magnetic layer is preferred in this example since Ku·v/kT increases more.
The effect of adding copper (Cu) to the third magnetic layer (18) was studied from the view point of S/Nd, an overwrite characteristic and thermal stability. In the study, the R/W performance of media whose Cu concentration in the third magnetic layer (MAGLAY3) was changed was measured. Magnetic recording media were formed in the same manner as described in Example 1 except for changing the composition of the third magnetic layer. The following six alloy targets were used for the third magnetic layer.
Magnetic recording media were formed by controlling the film thicknesses of the second and third magnetic layers so that Br3·t3=Br2·t2−Br1 t1 at about Br·t=8 T·nm.
In all of media in the example shown in
As a result of the study described above, to ensure the overwrite characteristic, the concentration of Cu added to the third magnetic layer is preferably about 4 at. % or less. Further, the concentration of Cu added to the third magnetic layer is preferably about 1 at. % or more since the thermal stability is improved. This can be explained as below. When Cu is added to the Co-based alloy containing Pt, Cr and B, since the segregation of Cr during film formation is promoted and the anisotropic energy of the magnetic film is increased, the thermal stability is improved. However, when the concentration of Cu added to the third magnetic layer is excessive, since magnetization of the magnetic layer decreases, the film thickness increases for keeping Br·t constant, and the overwrite characteristic is deteriorated.
As described above, a magnetic recording medium having an adequate S/Nd to attain an areal recording density of 150 or more Mbit per 1 m2, an excellent O/W characteristic and higher thermal stability could be attained. Further, application of a bias voltage from −100 to −400 V to the substrate during film formation of third magnetic layer is preferred in this example since Ku·v/kT increases more.
The effect of adding tantalum (Ta) and copper (Cu) to the third magnetic layer (18) was studied from the view point of S/Nd, an overwrite characteristic and thermal stability. In the study, the R/W performance of media whose Cu concentration in the third magnetic layer (MAGLAY3) was changed was measured. Magnetic recording media were formed in the same manner as described in Example 1 except for changing the composition of the third magnetic layer. The following four alloy targets were used for the third magnetic layer.
Magnetic recording media were formed by controlling the film thicknesses of the second and third magnetic layers so that Br3·t3=Br2·t2−Br1·t1 at about Br·t=8 T·nm.
As shown in
As a result of the study described above, to ensure the overwrite characteristic, it is preferred that the total content of Ta and Cu added to the third magnetic layer is about 4 at. % or less. Further, it is preferred that the total content of Ta and Cu added to the third magnetic layer is about 1 at. % or more since the thermal stability is improved. Thus, a magnetic recording medium having an adequate S/Nd to attain an areal recording density of 150 or more Mbit per mm2, an excellent O/W characteristic and higher thermal stability can be obtained.
Further, application of a bias voltage from −100 to −400 V to the substrate during film formation of the third magnetic layer is preferred in this embodiment since Ku·v/kT is further increased.
The concentration of platinum (Pt) in the second and third magnetic layers (16, 18) was studied from the view point of S/Nd, an overwrite characteristic and thermal stability. Magnetic recording media were formed in the same manner as described in Example 1 except for changing the composition of the second magnetic layer. The following four alloy targets were used for the second magnetic layer.
Magnetic recording media were formed by controlling the film thicknesses of the second and the third magnetic layers so that Br3·t3=Br2·t2−Br1·t1 at about Br·t=8 T·nm.
Ku·v/kT of 71 or more was obtained on all media of this example in
As described above, when the concentration of Pt contained in the second magnetic layer is less than that in the third magnetic layer, the overwrite characteristic and S/Nd are improved. In particular, it is not preferred the concentration of Pt contained in the second magnetic layer is greater than that in the third magnetic layer since the overwrite characteristic is deteriorated. Thus, a magnetic recording medium having an adequate S/Nd to attain an areal recording density of 150 or more Mbit per mm2, an excellent O/W characteristic and sufficient stability against thermal fluctuation can be obtained.
A suitable thickness for the second intermediate layer (17) that attains anti-ferromagnetical coupling between the second and third magnetic layers (16, 18) was studied from the view point of S/Nd, an overwrite characteristic and thermal stability. In the study, magnetic recording media were formed in the same manner as described in Example 1 except for setting the film thickness of the second intermediate layer on 0 nm, 0.3 nm, 0.5 nm, 0.7 nm, 0.9 nm, 1.0 nm, 1.2 nm, 1.5 nm and 2.0 nm.
From the results of the study described above, a magnetic recording medium having an adequate S/Nd to attain an areal recording density of 150 or more Mbit per mm2, an excellent O/W characteristic and sufficient stability against thermal fluctuation can be attained by setting the film thickness (Th) of the second intermediate layer within a range from about 0.5 to 1.2 nm.
The dependence on the film thickness of the second intermediate layer (17) attaining the anti-ferromagnetical coupling between the second and third magnetic layers (16, 18) was studied from the view point of S/Nd, an overwrite characteristic and thermal fluctuation. Instead of the 0.8 nm-thick second intermediate layer comprising Ru in Example 1, Ru-10 at. % Cr, Ru-20 at. % Cr, Ru-30 at. % Cr, Ru-10 at. % Fe, Ru-20 at. % Fe, and Ru-30 at. % Fe were each formed on a thickness of 0.3 nm, 0.5 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1.0 nm, 1.2 nm, 1.5 nm and 2.0 nm. Magnetic recording media were formed in the same manner as described in Example 1 except for the foregoing. S/Nd, O/W, and Ku·v/kT of the media were evaluated.
It is preferred that the second intermediate layer (17) formed between the second magnetic layer and the third magnetic layer is an alloy comprising Ru as the main ingredient and has a thickness of from about 0.5 to 1.2 nm. Also in a case of forming the second intermediate layer by sputtering a target containing Ru, the layer may sometimes contain the constituent elements in the upper and lower layers. When the thickness of the second intermediate layer is about 0.5 nm or less, medium noise attributable to the increase of the exchange coupling increases, and S/Nd decreases extremely. S/Nd is improved most when the thickness of the second intermediate layer is set on from about 0.5 nm to 1.2 nm. When the thickness of the second intermediate layer is more than about 1.2 nm, the S/Nd and the overwrite characteristic are gradually lowered. Accordingly, it is preferred that the second intermediate layer comprises Ru as the main ingredient and has a thickness within a range from about 0.5 to 1.2 nm. As described above, a magnetic recording medium having an adequate S/Nd to attain an areal recording density of 150 or more Mbit per mm2, an excellent O/W characteristic and sufficient stability against thermal fluctuation.
It is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims alone with their full scope of equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-262853 | Sep 2004 | JP | national |
