Patent Application
20180254059
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2017-040688, filed Mar. 3, 2017, the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a disk-like magnetic recording medium and a magnetic recording and reproducing device.
Among magnetic recording and reproducing devices, not only high recording capacity but also high data access performance is required of magnetic recording and reproducing devices which are designed for enterprises. In particular, an improvement of linear recording density (BPI) is required of sequential access performance.
In a magnetic recording and reproducing device using a conventional magnetic recording medium, the problem is that performance of a write operation in a high-speed transfer operation tends to decline in an outer circumferential area where a circumferential speed is high and this prevents an improvement of BPI.
To solve this problem, a method of compensating the decline of the performance of the write operation in the outer circumferential area by increasing a recording current to be applied to a recording head and increasing a magnetic flux to be produced from the recording head has been proposed.
However, the increase of the recording current leads to magnetic saturation of a magnetic shield which surrounds the magnetic head. For example, in a circumferential direction, a magnetic field gradient is decreased to deteriorate an S/N ratio due to magnetic saturation of a write shield, and in a radial direction, recorded information of adjacent tracks or tracks over a wide region is degraded or erased due to magnetic saturation of a side shield.
In general, according to one embodiment, a magnetic recording medium has the shape of a disk, and includes a disk-like substrate, a multilayer soft magnetic layer, and a magnetic recording layer.
The multilayer soft magnetic layer used in the embodiment includes a first soft magnetic layer, a nonmagnetic spacer layer, and a second soft magnetic layer which is antiferromagnetically exchange-coupled (AFC) with the first soft magnetic layer via the nonmagnetic spacer layer.
The magnetic recording medium of the embodiment can be divided into the following three types in terms of the strength of the exchange coupling magnetic field and the thickness of the nonmagnetic spacer layer.
In the magnetic recording medium of the first embodiment, the strength of the exchange coupling magnetic field Hbias decreases from the inner circumferential area toward the outer circumferential area of the disk-like magnetic recording medium.
In the magnetic recording medium of the second embodiment, the thickness x of the nonmagnetic spacer layer decreases from the inner circumferential area toward the outer circumferential area.
In the magnetic recording medium of the third embodiment, the thickness x of the nonmagnetic spacer layer increases from the inner circumferential area toward the outer circumferential area.
Further, the second embodiment and the third embodiment are further limited to the extent that the value of the exchange coupling magnetic field Hbias changes periodically with respect to the thickness x of the nonmagnetic spacer layer, and a relationship expressed as 0<x≤a is satisfied in the second embodiment, and a relationship expressed as a≤x<b is satisfied in the third embodiment, where a is a thickness of the nonmagnetic spacer layer when the exchange coupling magnetic field Hbias has a maximum value (first peak), c is a thickness of the nonmagnetic spacer layer when the exchange coupling magnetic field Hbias has a maximum value (second peak) after the first peak, and b is a thickness of the nonmagnetic spacer layer when the exchange coupling magnetic field Hbias has a minimum value between the first peak and the second peak.
Here, the exchange coupling magnetic field Hbias represents the degree of antiferromagnetic coupling between the first soft magnetic layer and the second soft magnetic layer.
The exchange coupling magnetic field Hbias can be measured by a vibrating sample magnetometer (VSM) manufactured by, for example, Toei Industry Co., Ltd. After the first soft magnetic layer, the nonmagnetic spacer layer, and the second soft magnetic layer are sequentially formed on the substrate.
Note that, for example, when a disk-like magnetic recording medium having an opening is divided into an area including an opening edge, an area including an outer edge, and an intermediate area therebetween, the inner circumferential area corresponds to the area including the opening edge. Further, the outer circumferential area corresponds to the area including the outer edge.
It is possible to combine the first embodiment with the second embodiment or combine the first embodiment with the third embodiment.
In the first embodiment, the strength of the exchange coupling magnetic field can be gradually reduced from the inner circumferential area toward the outer circumferential area.
In the second and third embodiments, the thickness of the nonmagnetic spacer layer can be gradually reduced or gradually increased from the inner circumference toward the outer circumference.
According to the embodiments, it is possible, by reducing Hbias from the inner circumferential area toward the outer circumferential area of the magnetic recording medium or reducing or increasing the thickness of the nonmagnetic spacer layer from the inner circumference toward the outer circumference in a range where Hbias can be reduced, to prevent the decline of the performance of the write operation in the high-speed transfer operation and improve the linear recording density in the outer circumferential area of the disk-like magnetic recording medium while maintaining or improving the capacity.
Embodiments will be described hereinafter with reference to the accompanying drawings.
As shown in the drawing, a magnetic recording medium 10 includes a substrate 1, a soft magnetic undercoating layer (SUL) 5 which includes a first soft magnetic layer 2, a nonmagnetic spacer layer 3, and a second soft magnetic layer 4 which is antiferromagnetically coupled (AFC) via the nonmagnetic spacer layer 3 sequentially on the substrate 1, and a magnetic recording layer 6 on the soft magnetic undercoating layer (SUL) 5.
As the substrate, a glass substrate, an Al alloy substrate, a ceramic substrate, a carbon substrate, a single crystalline Si substrate having an oxidized surface, or the like can be used.
As the first soft magnetic layer, a Co alloy containing Co and at least one of Zr, Hf, Nb, Ta, Ti and Y such as a CoZr alloy, a CoZrNb alloy or a CoZrTa alloy can be used.
As the nonmagnetic spacer layer, Ru, a Ru alloy, Pd, Cu, Pt or the like can be used.
As the second soft magnetic layer, a Co alloy containing Co and at least one of Zr, Hf, Nb, Ta, Ti and Y such as a CoZr alloy, a CoZrNb alloy or a CoZrTa alloy can be used. The composition of the first soft magnetic layer may be the same as that of the second soft magnetic layer and may also be different from that of the second soft magnetic layer.
As the magnetic recording layer, a material mainly containing Pt and either one of Fe and Co can be used.
For example, the magnetic recording layer has a granular structure which contains CoCrPt, FePt, CoPt, CoCrTa, SmCo or TbFeCo, and an oxide such as SiO2 or TiO2 as a grain boundary segregation material between the magnetic grains.
As shown in the drawing, except that an intermediate layer 6 is further provided between the soft magnetic undercoating layer 5 and the magnetic recording layer 7, and a protection layer 8 and a lubrication layer 9 are further provided sequentially on the magnetic recording layer 7, the structure of a magnetic recording medium 20 is the same as the structure shown in
As the intermediate layer, a Ru alloy, a Ni alloy, a Pt alloy, a Pd alloy, a Ta alloy, a Cr alloy, a Si alloy, a Cu alloy or the like can be used.
The protection film contains C.
As the lubricant, perfluoropolyether, fluoroalcohol or fluorinated carboxylic acid can be used.
The magnetic recording medium of the embodiment can be manufactured by the following processes.
Firstly, a substrate is accommodated in a film deposition chamber of a DC magnetron sputtering device, and an air is discharged from the film deposition chamber.
Then, inert gas such as Ar gas is introduced into the film deposition chamber, and a first soft magnetic layer, a nonmagnetic spacer layer, a second soft magnetic layer, an intermediate layer, and a recording layer are sequentially formed on an Al alloy substrate.
After that, a DLC protection layer is formed by a CVD method, and a lubricant is applied by a dipping method.
An example of the process for reducing Hbias from the inner circumferential area toward the outer circumferential area of the disk-like magnetic recording medium will be described below.
The strength of Hbias relies on the thickness of the nonmagnetic spacer layer and peaks when the nonmagnetic spacer layer has a predetermined thickness as shown in a graph 303.
It is possible, by increasing the thickness x of the nonmagnetic spacer layer from the inner circumferential area toward the outer circumferential area of the disk-like magnetic recording medium in such a manner as to satisfy an inequality defined as a≤x<b, where a is a thickness of the nonmagnetic spacer layer when Hbias has a maximum value (the first peak), c is a thickness of the nonmagnetic spacer layer when Hbias is at the second peak, and b is a thickness of the nonmagnetic spacer layer when Hbias has a minimum value between the first peak and the second peak, to reduce Hbias from the inner circumferential area toward the outer circumferential area of the disk.
It is also possible, by reducing the thickness x of the nonmagnetic spacer layer from the inner circumferential area toward the outer circumferential area of the disk-like magnetic recording medium in such a manner as to satisfy an inequality defined as 0<x≤a, where a is a thickness of the nonmagnetic spacer layer when Hbias has a maximum value, to reduce Hbias from the inner circumferential area toward the outer circumferential area of the disk.
In the magnetic recording medium of the second embodiment, a film thickness control method for forming the nonmagnetic spacer layer whose thickness decreases from the inner circumferential area toward the outer circumferential area will be described with reference to
As shown in
To satisfy the inequality defined as 0<x≤a, it is possible to make adjustments, for example, by setting a sputtering rate to 0.5 nm/s and setting a sputtering time to 2 seconds.
As shown in
As shown in
Further, when a film deposition process is performed in the arrangement shown in
When a film deposition process is performed in the arrangement shown in
In the magnetic recording medium of the third embodiment, a film thickness control method for forming the nonmagnetic spacer layer whose thickness increases from the inner circumferential area toward the outer circumferential area will be described with reference to
As shown in
As shown in
As shown in
Further, when a film deposition process is performed in the arrangement shown in
When a film deposition process is performed in the arrangement shown in
As shown in the drawing, a magnetic recording and reproducing device 130 includes a housing 131 which has the shape of a rectangular box whose upper surface is open, and a top cover (not shown) which is secured to the housing 131 with a plurality of screws and closes the upper end opening of the housing.
In the housing 131, a magnetic recording medium 132 of the embodiment, a spindle motor 133 as a driving means which supports and rotates the magnetic recording medium 132, a magnetic head 134 which records and reproduces a magnetic signal with respect to the magnetic recording medium 132, a head actuator 135 which includes a suspension whose tip is provided with the magnetic head 134, and movably supports the magnetic head 134 with respect to the magnetic recording medium 132, a rotating shaft 136 which rotatably supports the head actuator 135, a voice coil motor 137 which rotates and positions the head actuator 135 via the rotating shaft 136, a head amplifier circuit board 138, and the like.
Examples of the embodiments will be described in details.
The magnetic recording medium of the embodiment can be manufactured by the following processes.
Firstly, an Al alloy substrate of 3.5 inches is accommodated in a film deposition chamber of a DC magnetron sputtering device, and an air is discharged from the film deposition chamber.
Next, inert gas such as Ar gas is introduced into the film deposition chamber, and a first soft magnetic layer of CoFeTaZr, a nonmagnetic spacer layer of Ru, a second soft magnetic layer of CoFeTaZr, an intermediate layer of Ru, and a magnetic recording layer of CoCrPt—SiO2 are sequentially formed on the Al alloy substrate.
After that, a DLC protection layer is formed by a CVD method, a lubricant is applied by a dipping method, and a perpendicular magnetic recording medium of 3.5 inches is obtained.
The obtained perpendicular magnetic recording medium has a structure similar to the structure shown in
In the process of forming the nonmagnetic spacer layer in the example 1, as shown in
The thickness of the nonmagnetic spacer layer in the outer circumferential area is 1.5 nm, and the exchange coupling magnetic field (Hbias) is 50 Oe, while the thickness of the nonmagnetic spacer layer in the inner circumferential area is 1.0 nm, and Hbias is 135 Oe.
In the perpendicular magnetic recording medium of the example 1, the thickness of the nonmagnetic spacer layer increases from the inner circumferential area toward the outer circumferential area of the disk, and the strength (Hbias) of the exchange coupling magnetic field decreases from the inner circumferential area toward the outer circumferential area of the disk-like magnetic recording medium.
In
In
The magnetic recording medium of each of the example 1, the comparative example 1 and the comparative example 2 is mounted on the magnetic recording and reproducing device, and the overwrite characteristics (OW1 and OW2), the linear recording density (BPI), the track recording density (TPI), and the areal recording density (ADC) which is expressed as a product of BPI and TPI are evaluated.
Note that the evaluation is carried out under the condition that, in the magnetic recording medium of 3.5 inches, the outer circumferential area is located in a radius of 44 mm, and the inner circumferential area is located in a radius of 19 mm.
In OW1, when an overwrite operation is performed at a frequency higher than that of a single frequency pattern which is recorded as a foundation, a ratio between signal output of the foundation before and after the overwrite operation is shown. As OW1 increases, the performance of the high-frequency write operation improves.
On the other hand, in OW2, when an overwrite operation is performed at a frequency lower than that of a single frequency pattern which is recorded as a foundation, a ratio between signal output of the foundation before and after the overwrite operation is shown. As OW2 increases, the performance of the low-frequency write operation improves.
The measurement results are shown in the following table 1.
In the outer circumferential area, both OW1 and OW2 are improved in each of the example 1 and the comparative example 2 with respect to the comparative example 1, and BPI is increased by 4.5%. On the other hand, as OW is improved, write bleeding in a track width direction is increased, and therefore TPI is reduced by 2.8%. However, since a large improvement is made in BPI in each of the example 1 and the comparative example 2 with respect to the comparative example 1, ADC is increased by 1.6%.
In the inner circumferential area, since Hbias of the example 1 is the same as that of the comparative example 1, the performance remains the same. In the comparative example 2, although both OW1 and OW2 are improved with respect to the comparative example 1, since the circumferential speed of the inner circumferential area is lower than that of the outer circumferential area, the improvement in OW1 is small, and the improvement in BPI is also small as compared to the outer circumferential area and the increase remains at 1.8%. On the other hand, the write bleeding in the track width direction is greatly influenced by OW2 of the performance of the low-frequency write operation, and TPI is reduced by 3.6%. In the comparative example 2, ADC is reduced by 1.8%.
As compared to the comparative example 1, the example 1 shows an increase of 1.6% in ADC in the outer circumferential area and the inner circumferential area in total, and also shows an improvement in BPI in the outer circumferential area.
As compared to the comparative example 1, the comparative example 2 shows an improvement in BPI in the outer circumferential area but also shows a decrease of 0.2% in ADC in the outer circumferential area and the inner circumferential area in total.
The above results show that, when Hbias of the outer circumferential area is lower than that of the inner circumferential area, BPI improves while the capacity remains the same or improves.
Next, when the sputtering time of the nonmagnetic spacer layer is changed from 2 seconds to 3 seconds and Hbias of the inner circumferential area is changed from 135 Oe to 30 Oe, BPI of the outer circumferential area is measured. A condition for the upper limit of Hbias of the outer circumferential area which can improve BPI in the outer circumferential area and will not degrade ADC in the outer circumferential area and the inner circumferential area in total are examined.
Hbias (ID_Hbias) of the inner circumferential area is plotted on the horizontal axis, and the upper limit of Hbias (OD_Hbias) of the outer circumferential area under the condition that ADC in the outer circumferential area and the inner circumferential area in total will not be degraded is plotted on the vertical axis, and a graph 101 is obtained.
As shown in the graph 101, since the upper limit of the OD_Hbias under the condition changes linearly with respect to the ID_Hbias, the upper limit of the OD_Hbias with respect to the ID_Hbias can be set within a range which satisfies the following inequality (1):
OD_Hbias<1.16×ID_Hbias−22.8 (1)
where ID_Hibas≥30.
An Al alloy substrate of 3.5 inches is accommodated in a film deposition chamber of a DC magnetron sputtering device, and an air is discharged from the film deposition chamber.
Next, inert gas such as Ar gas is introduced into the film deposition chamber, and on an Al alloy substrate, a soft magnetic undercoating layer (SUL) which is composed of a first soft magnetic layer of CoFeTaZr, a nonmagnetic spacer layer, and a second soft magnetic layer of CoFeTaZr is formed, and on the SUL, an intermediate layer and a magnetic recording layer of CoCrPt—SiO2 are sequentially formed.
After that, a DLC protection layer is formed by a CVD method, a lubricant is applied by a dipping method, and a magnetic recording medium is obtained.
The obtained perpendicular magnetic recording medium has a structure similar to the structure shown in
In the process of forming the nonmagnetic spacer layer in the example 2, as shown in
The thickness of the nonmagnetic spacer layer in the outer circumferential area is 0.5 nm, and the exchange coupling magnetic field (Hbias) is 50 Oe, while the thickness of the nonmagnetic spacer layer in the inner circumferential area is 1.0 nm, and Hbias is 135 Oe. In the magnetic recording medium of the comparative example 1, Hbias is 135 Oe both in the outer circumferential area and in the inner circumferential area. In the magnetic recording medium of the comparative example 2, Hbias is 50 Oe both in the outer circumferential area and in the inner circumferential area.
The magnetic recording medium of each of the example 1, the comparative example 1 and the comparative example 2 is mounted on the magnetic recording and reproducing device, and the overwrite characteristics (OW1 and OW2), the linear recording density (BPI), the track recording density (TPI), and the areal recording density (ADC) which is expressed as a product of BPI and TPI are evaluated. Note that the evaluation is carried out under the condition that the outer circumferential area is located in a radius of 44 mm, and the inner circumferential area is located in a radius of 19 mm.
The measurement results are shown in the following table 2.
In the outer circumferential area, both OW1 and OW2 are improved in each of the example 2 and the comparative example 2 with respect to the comparative example 1, and BPI is increased by 4.5%. On the other hand, as OW is improved, the write bleeding in the track width direction is increased, and therefore TPI is reduced by 2.8%. However, since a large improvement is made in BPI in each of the example 2 and the comparative example 2 with respect to the comparative example 1, ADC is increased by 1.6%.
In the inner circumferential area, since Hbias of the example 2 is the same as that of the comparative example 1, the performance remains the same. In the comparative example 2, although both OW1 and OW2 are improved with respect to the comparative example 1, since the circumferential speed of the inner circumferential area is lower than that of the outer circumferential area, the improvement in OW1 is small, and the improvement in BPI is also small as compared to the circumference and the increase remains at 1.8%. On the other hand, the write bleeding in the track width direction is greatly influenced by OW2 of the performance of the low-frequency write operation, and TPI is reduced by 3.6%. In the comparative example 2, ADC is reduced by 1.8%.
As compared to the comparative example 1, the example 2 shows an increase of 1.6% in ADC in the outer circumferential area and the inner circumferential area in total, and also shows an improvement in BPI in the outer circumferential area. As compared to the comparative example 1, the comparative example 2 shows an increase in BPI in the outer circumferential area but also shows a decrease of 0.2% in ADC in the outer circumferential area and the inner circumferential area in total.
The above results show that, when Hbias of the outer circumferential area is lower than that of the inner circumferential area, BPI improves while the capacity remains the same or improves.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-040688 | Mar 2017 | JP | national |
