Patent Application
20110181987
The present invention relates to a magnetic head mounted on a magnetic recording/reproducing apparatus, and particularly to a magneto-resistive head for reproducing information recorded on a magnetic medium.
In recent years, the magnetic recording/reproducing apparatus such as an HDD (Hard Disk Drive) has been required to quickly increase areal density, and the magnetic head and the magnetic media and the like are also required to provide high areal density. The magneto-resistive head mounted on the magnetic recording/reproducing apparatus as the reproducing sensor uses a structure called a spin-valve using the magneto-resistive effect of a multilayer film formed by laminating ferromagnetic metal-layers with a nonmagnetic metal layer sandwiched therebetween. The magneto-resistive effect is a phenomenon in which the electrical resistance varies depending on the angle between the magnetizations of two ferromagnetic layers sandwiching a nonmagnetic intermediate layer. The spin-valve using the magneto-resistive effect has a structure of an antiferromagnetic layer/a ferromagnetic layer/a nonmagnetic intermediate layer/a ferromagnetic layer. This structure provides an output by substantially fixing the magnetization of the ferromagnetic layer contacting the antiferromagnetic layer by an exchange coupling field generated in the interface between the antiferromagnetic layer and the ferromagnetic layer and by freely rotating the magnetization of the other ferromagnetic layer by an external field. The ferromagnetic layer whose magnetization is substantially fixed by the antiferromagnetic layer is called a reference layer. The ferromagnetic layer whose magnetization is rotated by the external field is called a free layer.
Conventionally, for the spin-valve using the magneto-resistive effect, a CIP (Current In the Plane)-GMR (Giant Magneto-Resistive) head used to flow current in the in-plane direction of the laminated film has been adopted. Currently, the CIP-GMR head is being replaced with a TMR (Tunneling Magneto-Resistive) head and a CPP (Current Perpendicular to the Plane)-GMR head used to flow current in the film thickness direction of the laminated film.
There are two major reasons for the replacement of the CIP-GMR head with the TRM head and the CPP-GMR head. The first reason is that the TMR head and CPP-GMR head can increase the read output more than the CIP-GMR head, and thereby can provide high SNR (output/noise ratio). The second reason is that the CPP type of flowing current in the perpendicular direction of the laminated film is more advantageous than the CIP type of flowing current in the in-plane direction of the laminated film in terms of increasing the linear density. The linear density is the bit density in the circumferential direction of magnetic medium. Note that the bit density in the radius direction of the magnetic medium is called a track density. An increase in both the linear density and the track density improves the areal density of the magnetic recording/reproducing apparatus. The increase in the linear density requires improvement in the resolution. The resolution is an index indicating how high the read output can be maintained in high density recording, compared to in low density recording.
Note that the current magneto-resistive head has a structure (so-called shield-type-read head) in which a magneto-resistive film is sandwiched between a lower magnetic shield and an upper magnetic shield. The resolution in the linear density direction depends largely on the gap (Gs) between the upper and lower magnetic shields. In other words, the smaller the gap between the upper and lower magnetic shields is, the higher the resolution in the linear density direction is, and thus high areal density can be achieved.
The conventional CIP-GMR head needs to electrically isolate the magneto-resistive film from the upper and lower magnetic shields and thus needs to interpose an insulating film between the upper and lower magnetic shields and the magneto-resistive film respectively. For this reason, it has been difficult to reduce the gap between the upper and lower magnetic shields. On the other hand, the TMR and CPP-GMR heads flowing current in the film thickness direction of the laminated film do not need to interpose an insulating layer between the upper and lower magnetic shields and the magneto-resistive film, which is advantageous in reducing the gap between the upper and lower magnetic shields. For this reason, the magneto-resistive head is shifting from the CIP-GMR head to the TMR and CPP-GMR heads, to increase the output and to improve resolution.
However, it is thought that it is impossible to reduce the film thickness of the CPP type magneto-resistive film to about 30 nm or less, and that the resolution improvement will reach a limit in the near future. The reason is that the film thickness of the above described magneto-resistive film (an antiferromagnetic layer/a ferromagnetic layer/a nonmagnetic intermediate layer/a ferromagnetic layer) has a physical limit of about 30 nm. For this reason, the read head of the current structure imposes a physical limit of about 30 nm on the gap between the upper and lower magnetic shields, which is a major impediment to providing high areal density.
A so-called differential read head has been proposed as means for improving the resolution in the linear density direction. In the in-plane magnetic recording system, a signal field is generated only from a magnetization reversal region with respect to a recorded bit written in a magnetic medium, while in the perpendicular magnetic recording system, a signal field is always generated from each recorded bit. For this reason, the perpendicular magnetic recording system is suitable for use in the differential read head.
Patent Document 1 discloses a read head structure in which a pair of magneto-resistive films is coupled in series with a conductive layer sandwiched therebetween for differential operation in a magnetic recording/reproducing apparatus using the perpendicular magnetic recording system. The two free layers of the pair of magneto-resistive films are disposed adjacent to and facing each other via the conductive layer to serve as a magnetic sensing unit for sensing a signal field, and the resistance change characteristics of the pair of magneto-resistive films have opposite polarity to the magnetic field in the same direction, which enables differential operation. In this case, the resolution in the linear density direction is more influenced by the inside distance between the free layers than the gap between the upper and lower magnetic shields. Therefore, even if the gap between the upper and lower magnetic shields cannot be reduced, a high resolution in the linear density direction can be obtained by reducing the film thickness of the conductive layer interposed between the pair of magneto-resistive films.
Further, Patent Document 2 discloses a detailed structure of the differential read head in which two free layers have resistance change characteristics of opposite polarity to the magnetic field in the same direction. Furthermore, Patent Document 3 discloses a structure of the read head which provides high resolution without the upper and lower magnetic shields.
Patent Document 1: JP 2002-183915 A
Patent Document 2: JP 2003-69109 A
Patent Document 3: JP 2004-227749 A
Non Patent Document 1: H. N. Bertram, Theory of magnetic recording (1994)
The differential read head has a problem in that when there is difference between the output characteristics (except the polarity to the magnetic field) of the two magneto-resistive sensors, a base line shift occurs in the waveform. There have been no reports as to how the base line shift affects the read/write characteristics of a magnetic disk apparatus. In light of this, the present inventors studied the effects of the base line shift on the read/write characteristics and have found that the base line shift does not affect the read output, resolution, SNR, or the like, but deteriorates the bit error rate.
Therefore, the differential head needs to control the output of the two magneto-resistive sensors as equally as possible. The output of each magneto-resistive sensor is in proportion to the product of the utilization e, the maximum resistance change DR, and the sense current Is. Here, the utilization is defined as dR/DR which is a ratio between the resistance change amount dR when a medium field is applied to the individual magneto-resistive sensors and the maximum resistance change DR.
When the read head is a CPP-type, the sense current flowing in the individual magneto-resistive sensors is constant. Therefore, the difference between the outputs of the individual magneto-resistive sensors is caused only by the difference between the maximum resistance change of the individual magneto-resistive sensors and the utilization thereof. The utilization can be controlled by changing the magnetic domain control field applied to the individual free layers. A general method of controlling the magnetic domain control field includes adjustment of the film thickness of a magnetic domain control layer provided on both sides in the track width direction of the magneto-resistive sensor and the distance between a magneto-resistive sensor and a magnetic domain control layer.
However, if the distance in the track width direction between the free layer and the magnetic domain control layer and the geometric positional relation in the film thickness direction between the free layer and the hard magnetic layer cannot be made identical, there has been invented a structure including a bias field application layer which sandwiches a laminated structure containing a ferromagnetic layer between nonmagnetic layers and is used for the magneto-resistive sensor to apply a bias field along the track direction. This configuration has a structure in which each magneto-resistive sensor has the same maximum resistance change.
Meanwhile, the maximum resistance change has a problem in that even if a first magneto-resistive film and a second magneto-resistive film are made under the same conditions, a difference in maximum resistance change occurs. The maximum resistance change is sensitive to the smoothness of the film thickness of each magneto-resistive sensor, the crystal orientation of the underlying film, and other conditions. Regarding the smoothness of the film thickness, the first magneto-resistive sensor to be made first tends to be better than the second magneto-resistive sensor. Thus, the maximum resistance change of the first magneto-resistive sensor is often larger than the maximum resistance change of the second magneto-resistive sensor. However, when the second magneto-resistive film has a good underlying orientation, the maximum resistance change of the second magneto-resistive sensor tends to be larger than the maximum resistance change of the first magneto-resistive sensor. The underlying layer of the second magneto-resistive film corresponds to an intermediate layer between the first magneto-resistive film and the second magneto-resistive film and has a relatively thick film thickness of several 10 nm. For this reason, the second magneto-resistive film is likely to have a good orientation. Note that there is a possibility that the maximum resistance change of the individual magneto-resistive sensors can be substantially equal by independently adjusting the materials, the film thickness, and like of the free layer, the intermediate layer, and the reference layer. However, if the individual magneto-resistive sensor has a widely different configuration of the free layer, the intermediate layer, and the reference layer, the individual magneto-resistive sensor has a different magnetic characteristic. Thus, it is easy to expect that a problem will occur.
An object of the present invention is to provide a magneto-resistive head which is a differential magneto-resistive head having a high resolution in a linear density direction and provides a good bit error rate without base line shift even if two magneto-resistive sensors have a different maximum resistance change by independently controlling a magnetic domain control field to be applied to the two magneto-resistive sensors.
In order to solve the above problems, a read head according to the present invention has a differential read head having a laminated structure in which a first magneto-resistive sensor having a first free layer, a differential gap layer, a second magneto-resistive sensor having a second free layer are laminated. Further, in order to provide a structure for obtaining a waveform without base line shift, any one of the following two configurations is adopted.
(A) A configuration having a magneto-resistive film and a magnetic control film in which magnetic domain control field HB1 applied to a first magneto-resistive sensor is larger than magnetic domain control field HB2 applied to a second magneto-resistive sensor in a differential read head in which maximum resistance change DR1 of the first magneto-resistive sensor is larger than maximum resistance change DR2 of the second magneto-resistive sensor.
(B) A configuration having a magneto-resistive film and a magnetic control film in which magnetic domain control field HB2 applied to the second magneto-resistive sensor is larger than magnetic domain control field HB1 applied to the first magneto-resistive sensor in a differential read head in which maximum resistance change DR2 of the second magneto-resistive sensor is larger than maximum resistance change DR1 of the first magneto-resistive sensor.
Here, a more detailed configuration for achieving (A) will be described below.
1) A configuration in which when a distance between a center in an end portion in a track width direction of a first free layer and a center of a bias film adjacent to the first free layer is set to D1, a distance between a center in an end portion in a track width direction of a second free layer and a center of a bias film adjacent to the second free layer is set to D2, a product of saturation magnetization of the first free layer and film thickness thereof is set to Ms1t1, and a product of saturation magnetization of the second free layer and film thickness thereof is set to Ms2t2, DR1/DR2 is equal to or greater than 1.05 and equal to or less than 5.0, Ms1t1/Ms2t2 is equal to or greater than 0.25 and equal to or less than 4.0, and D1 is greater than D2.
2) A configuration in which Ms1t1/Ms2t2 is equal to or greater than 0.25 and equal to or less than 4.0, DR1/DR2 is equal to or greater than 1.05 and equal to or less than 5.0, and the relation between DR1/DR2 and HB1/HB2 satisfies the following relation.
0.86×(DR1/DR2)<(HB1/HB2)
3) A configuration in which when the saturation magnetization of a region adjacent to the first free layer is set to MsHB1, and the saturation magnetization of a region adjacent to the second free layer is set to MsHB2, DR1/DR2 is equal to or greater than 1.05 and equal to or less than 5.0, and DR1/DR2, MsHB2 and HB1/HB2 satisfy the following relational expression.
0.8×(DR1/DR2)<(MsHB1/MsHB2)
Hereinafter, a more detailed configuration for achieving (B) will be described below.
1) A configuration in which when a distance between a center in an end portion in a track width direction of a first free layer and a center of a bias film adjacent to the first free layer is set to D1, a distance between a center in an end portion in a track width direction of a second free layer and a center of a bias film adjacent to the second free layer is set to D2, a product of saturation magnetization of the first free layer and film thickness thereof is set to Ms1t1, and a product of saturation magnetization of the second free layer and film thickness thereof is set to Ms2t2, DR1/DR2 is equal to or greater than 0.25 and equal to or less than 0.95, Ms1t1/Ms2t2 is equal to or greater than 0.25 and equal to or less than 4.0, and D1 is less than D2.
2) A configuration in which Ms1t1/Ms2t2 is equal to or greater than 0.25 and equal to or less than 4.0, DR1/DR2 is equal to or greater than 0.25 and equal to or less than 0.95, and the relation between DR1/DR2 and HB1/HB2 satisfies the following relation.
(HB1/HB2)<1.15×(DR1/DR2)
3) A configuration in which when the saturation magnetization of a region adjacent to the first free layer is set to MsHB1, and the saturation magnetization of a region adjacent to the second free layer is set to MsHB2, DR1/DR2 is equal to or greater than 0.25 and equal to or less than 0.95, DR1/DR2, MsHB1 and MsHB2 satisfy the following relational expression.
(MsHB1/MsHB2)<1.2×(DR1/DR2)
According to the present invention, a magnetic read/write head having a differential read head using two magneto-resistive sensors can provide a differential read head without base line shift by controlling a magnetic domain control field applied to the two magneto-resistive sensors. Further, the magnetic recording/reproducing apparatus can achieve a high linear density and a good bit error rate by mounting a magnetic read/write head combining such differential read head and write head on the magnetic recording/reproducing apparatus.
Hereinafter, a read head to which the present invention is applied, and a magnetic head and a magnetic recording apparatus having the same will be described in detail by referring to the drawings.
As illustrated in
As illustrated in
The following description focuses on a configuration example of the first reference layer 230 and the second reference layer 330 so that the first magneto-resistive sensor 200 and the second magneto-resistive sensor 300 exhibit opposite phase resistance changes in the same external magnetic field direction. The first reference layer 230 is a laminated film of the first antiferromagnetic layer 236 and a so-called synthetic ferry structure in which a number m (m: odd number) of ferromagnetic layers and an m−1 number of antiferromagnetic exchange coupling layers are alternately laminated. The second reference layer 330 is a laminated film of the second antiferromagnetic layer 334 and a so-called synthetic ferry structure in which a number n (n: even number) of ferromagnetic layers and an n−1 number of antiferromagnetic exchange coupling layers are alternately laminated. By doing so, the magnetization of the ferromagnetic layers (components of the first reference layer 230 and the second reference layer 330) contacting the first antiferromagnetic layer 236 and the second antiferromagnetic layer 334 is fixed to the same direction. In this case, the magnetization of the ferromagnetic layers (components of the first reference layer 230 and the second reference layer 330) contacting the first intermediate layer 220 and the second intermediate layer 320 substantially contributing to the magneto-resistive effect is fixed to the antiparallel direction. Therefore, the first magneto-resistive film 200 and the second magneto-resistive film 300 exhibit opposite phase resistance change characteristics to the signal fields in the same direction. Note that n may be an odd number and m may be an even number, which is not regarded as a departure from the spirit and scope of the present invention.
Now, the specific composition and film thickness of each component of the differential read head 20 illustrated in
The sputtering method is preferred for forming the first magneto-resistive film 200/the differential gap layer 100/the second magneto-resistive film 300 from the viewpoint of the controllability of film thickness and alloy composition as well as the mass production efficiency. A preferred configuration example of the first magneto-resistive film 200 is, for example, Ni85Fe15(2)/Co90Fe10(1)/MgO(1)/Co90Fe10(2.5)/Ru(0.45)/Co90Fe10(4)/Ru(0.45)/Co75Fe25(1.5)/Mn80Ir20(6). The numbers in parenthesis indicate the layer thickness in nm. The unit of each alloy composition indicated by the corresponding element suffix is at %. Mn80Ir20(6) corresponds to the first antiferromagnetic layer 236; Co75Fe25(2)/Ru(0.45)/Co90Fe10(2.5)/Ru(0.45)/Co90Fe10(2.5) corresponds to the first reference layer 230; MgO(1) corresponds to the first intermediate layer 220; and Co90Fe10(1)/Ni85Fe15(3) corresponds to the first free layer 210 respectively.
Note that Ta(3)/Ru(2) may be formed as an underlying layer of the first antiferromagnetic layer 236. Note also that here is shown an example of a TMR film using MgO as the first intermediate layer. However, in addition to MgO, an oxide containing Mg, Al, Si, Ti, V, Mn, Zr, Nb, Hf, Ta, and the like, or a nitride thereof, may also be used as the intermediate layer material. When the first intermediate layer is made of Cu, Ag, Au, or an alloy mainly containing such elements, the layer can be used as a CPP-GMR film as it is. Further, the first intermediate layer may be formed as a so-called “current-screen-type” structure in which a conductive path by a metallic pinhole such as Cu is formed in an insulating material such as Al2O3.
Likewise, a preferred configuration example of the second magneto-resistive film 300 may be Ni85Fe15(2)/Co90Fe10(1)/MgO(1)/Co90Fe10(2.5)/Ru(0.45)/Co90Fe10(3)/Mn80Ir20(6). A substantially symmetrical configuration of the first magneto-resistive film 200 in terms of the laminating order can provide substantially the same magnetic resistance change characteristics. In order to finely adjust the areal resistance and the magnetic resistance change ratio, mainly the film thickness of the intermediate layer may be appropriately optimized. The only difference is in the configuration of the reference layer. The second reference layer 330 in the second magneto-resistive film 300 is assumed as Co90Fe10(2.5)/Ru(0.45)/Co90Fe10(3). Both are configured as “synthetic ferry” in which a Co—Fe ferromagnetic layer and an Ru layer for antiferromagnetic exchange coupling are alternately laminated. The difference is that the first reference layer 230 in the first magneto-resistive film 200 includes a three-layered Co—Fe layer and the second reference layer 330 in the second magneto-resistive film 300 includes a two-layered Co—Fe layer. More specifically, the first reference layer 230 has a synthetic ferry structure in which a number m (m: odd number) of ferromagnetic layers and an m−1 number of antiferromagnetic exchange coupling layers are alternately laminated. The second reference layer 330 has a synthetic ferry structure in which a number n (n: even number) of ferromagnetic layers and an n−1 number of antiferromagnetic exchange coupling layers are alternately laminated.
By doing so, the magnetization of the ferromagnetic layers (components of the first reference layer 230 and the second reference layer 330) contacting the first antiferromagnetic layer 236 and the second antiferromagnetic layer 334 is fixed to the same direction. In this case, the magnetization of the ferromagnetic layers (components of the first reference layer 230 and the second reference layer 330) contacting the first intermediate layer 220 and the second intermediate layer 320 substantially contributing to the magneto-resistive effect is fixed to the antiparallel direction. Therefore, the first magneto-resistive film 200 and the second magneto-resistive film 300 exhibit opposite phase resistance change characteristics to the signal fields in the same direction, which is suitable for differential operation. Note that m may be an even number and n may be an odd number without causing any hindrance.
The specific composition of the differential gap layer 100 may include Cr, Cu, Pd, Ag, Ir, Pt, Au, Mo, Ru, Rh, Ta, W, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, or Er, or an alloy containing these elements. It should be noted that the material should be selected so as not to generate magneto-resistive effect between the first free layer 210 and the second free layer 310 through the differential gap layer 100. The metals which can be used for the differential gap layer 100 can be classified into the following three major groups: A (Cr, Cu, Pd, Ag, Ir, Pt, Au), B (Mo, Ru, Rh, Ta, W), and C (Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er). The differential read head using any of the metals of Group A has characteristics that the electrical resistance is lower than the other metals of Group B or C. The metals of Group B have characteristics that the resistance to physical polishing is greater than the other metals of Group A or C. The metals of Group C have characteristics that the spin torque noise caused by spin torque is smaller than the other metals of Group A or B. These elements can be appropriately selected according to the recording density of the magnetic recording/reproducing apparatus, which is the track width of the differential read head, the sensor size such as G1, and the electrical resistance value thereof.
The base line shift reduction effect characterizing the present invention's structure will be described below.
The cause for the base line shift will be described by referring to
Now, the description will focus on the cause for the difference between the outputs of the two magneto-resistive sensors and the method of reducing the difference between the outputs characterizing the present invention. The output of the individual magneto-resistive sensors is expressed by the following expression (1).
S
1,2
=DR
1,2
×e
1,2 (1)
Here, S1,2 denotes the output of the first and second magneto-resistive sensors 200 and 300. DR1,2 denotes the maximum resistance change of the first and second magneto-resistive sensors 200 and 300. e1,2 denotes the utilization of the first and second magneto-resistive sensors 200 and 300. The utilization indicates the sensitivity of the individual magneto-resistive sensor to the external magnetic field. The stronger the magnetic domain control field, the smaller the utilization is. In the configuration example of the present invention and the configuration example of the conventional structure illustrated in
In order to substantially equalize S1 and S2, in the present invention, the present invention's structure controls e1 and e2 independently according to the difference between DR1 and DR2. In the present configuration example, e1 is 20% and e2 is 25%. In general, the base line shift can be reduced using a configuration in which when DR1 is larger than DR2, e1 is smaller than e2, and when DR1 is smaller than DR2, e1 is larger than e2. In the present embodiment, DR1 is larger than DR2, and thus a configuration is used in which e1 is smaller than e2.
In order to make e1 smaller than e2, the HB1/HB2 ratio between the magnetic domain control field HB1 applied to the first magneto-resistive sensor 200 and the magnetic domain control field HB2 applied to the second magneto-resistive sensor 300 satisfies the following expression (2) according to the DR1/DR2 ratio between DR1 and DR2.
5≧DR1/DR2≧1.05 and HB1>HB2 (2)
Here, it is assumed that the Ms1t1/Ms2t2 ratio between the product Ms1t1 of the saturation magnetization Ms1 of the first free layer and the film thickness t1 and the product Ms2t2 of the saturation magnetization MS2 of the second free layer and the film thickness t2 is equal to or greater than 0.25 and equal to or less than 4.0. Further, it is assumed that HB1 and HB2 are an average value of the magnetic domain control fields in the film surfaces of the free layers. The size of the magnetic domain control field can be calculated by numerical calculation using finite element method from the magnetic domain control layer 450, the geometric shape of the laminated film structure, and the saturation magnetization of the magnetic domain control layer 450.
The reason why the utilization can be controlled by controlling the magnetic domain control field will be described using the following expression (3) and
e
1
/e
2
=HB
2
/HB (3)
Next,
The advantages of the present invention will be described below.
Baseline shift=b/a×100 (4)
As understood from
A specific configuration example according to the present invention will be described below. In the configuration example of the present invention illustrated in
On the contrary, in the configuration example of the conventional structure illustrated in
Finally, the description will focus on how the DR difference between the two magneto-resistive sensors is observed in the actual differential read head.
Another configuration example of the present invention will be described. Unlike the first embodiment, the present configuration example is configured such that DR1 is smaller than DR2. One of the reasons that the maximum resistance change of the second magneto-resistive sensor is larger is that the second magneto-resistive film has a good underlying orientation. This is because the underlying film of the second magneto-resistive film corresponds to the intermediate layer between the first magneto-resistive film and the second magneto-resistive film and has a relatively thick film thickness of several 10 nm which tends to have a good orientation.
Like the configuration of the first embodiment, the present configuration example can reduce the base line shift caused by the difference between DR1 and DR2 by controlling HB1 and HB2.
A specific structure of the present configuration example for reducing the base line shift will be described below. The present configuration example is the same as the configuration of the first embodiment except for the parameters HB1 and HB2, and thus the detailed configuration is omitted. In the present configuration, the positional relation between the magnetic domain control film and the magneto-resistive sensor is adjusted such that HB1/HB2 falls within the range illustrated in
HB
1
<HB
2 under 0.95≧DR1/DR2≧0.25 (5)
The reason why DR1/DR2 needs to be smaller than 0.95 is that when DR1/DR2 is smaller than 1.0 and larger than 0.95, the magnetic domain control film needs to be controlled so that HB1/HB2 is also smaller than 1.0 and larger than 0.95, but it is difficult to suppress the positional errors and the magnetic characteristic variations of the magnetic control film so as to fall within this range. Further, when DR1/DR2 is smaller than 0.25, HB1/HB2 also needs to be smaller than 0.25, but this is difficult because of the shape of the magnetic domain control film and the physical limitation of the material. Therefore, when DR1/DR2 is equal to or greater than 0.25 and equal to or less than 0.95, the configuration is made such that HB2 is larger than HB1.
Another configuration example of the present invention will be described. Like the first embodiment, the present configuration example can reduce the base line shift in the differential read head in which DR1 is larger than DR2. In the third embodiment, a particularly detailed description will be given of the method of controlling the magnetic domain control field of the two magneto-resistive sensors not described in the first embodiment. Regarding the method of controlling the magnetic domain control field, the relative positional relation and the geometric shape of the magnetic domain control layer 450 and the first and second free layers of the differential read head are set. The configuration of the two magneto-resistive sensors and the differential gap layer in the present configuration example is the same as that of the first embodiment, and thus the description duplicating the first embodiment will be omitted. In the present configuration example, in order to control the HB1/HB2 ratio of the magnetic domain control fields applied to the two free layers, the distance between the two free layers and the magnetic domain control layer 450 is controlled.
There are two major methods of controlling the distance between the two free layers and the magnetic domain control layer 450. One is a method of offsetting the magnetic domain control layer 450 in the film thickness direction like the configuration example illustrated in
First, a configuration example for the first method will be described.
D1<D2 (6)
Note that in the present configuration example, DR1/DR2 is equal to or greater than 1.05 and equal to or less than 5.0, Ms1t1/Ms2t2 is equal to or greater than 0.25 and equal to or less than 4.0. The reason for this is the same as described in the first embodiment. The range between DR1/DR2 and D1/D2 which is a condition of the present configuration is illustrated in
In the configuration example illustrated in
A configuration example for the second method is illustrated in
tr1<tr2 (7)
The range between DR1/DR2 and tr1/tr2 which is a condition of the present configuration is illustrated in
The first and second structures are the same in that the distance between the magnetic domain control layer 450 and the free layer is controlled. However, from the point of view of the reproduction process, the first structure has an advantage in that it is easier to position and can control HB1/HB2 relatively accurately. Meanwhile, the second structure has an advantage in that it can increase the difference between HB1 and HB2 more than the first structure. This is because the dependency of the distance between the magnetic domain control layer 450 and the free layer is stronger than that of the offset of the magnetic domain control layer 450. Thus, it is preferable that when the difference between DR1 and DR2 is small, the first method is used and when the difference between DR1 and DR2 is large, the second method is used.
Another configuration example of the present invention will be described. The present configuration example is used when DR1 is smaller than DR2. Like the configuration of the third embodiment, the present configuration example controls the shape of the magnetic domain control film and the magneto-resistive sensor to reduce the base line shift caused by the difference between DR1 and DR2 by controlling HB1 and HB2.
D1>D2 (8)
Note that in the present configuration example, DR1/DR2 is equal to or greater than 0.25 and equal to or less than 0.95 and Ms1t1/Ms2t2 is equal to or greater than 0.25 and equal to or less than 4.0. The reason for this is the same as described in the second embodiment. The present configuration can reduce the base line shift by controlling the positional relation between the magnetic domain control film and the magneto-resistive sensor.
There are two major methods of controlling the distance between the two free layers and the magnetic domain control layer 450. One is a method of offsetting the magnetic domain control layer 450 in the film thickness direction like the configuration example illustrated in
tr1>tr2 (9)
From the expression (9), tr1 and tt2 fall in the range illustrated in
Another configuration example of the present invention will be described below. The configuration example of a differential read head according to the fifth embodiment modifies the configuration example in the first embodiment or the third embodiment in such a manner that the range of HB1/HB2 is particularly made appropriate so that the size of the base line shift fall within 20%. In the fifth embodiment, the configuration of the two magneto-resistive sensors, the differential gap layer, and the magnetic domain control layer 450 is the same as described in the first embodiment, and thus the description is omitted.
The present invention's structure can always reduce the size of the base line shift to within 20%, and thus can suppress the deterioration amount of the bit error rate to at most 10−0.8 or less. It is a preferred range as the magnetic recording apparatus that the size of the line shift is within 20%.
The condition illustrated in
0.86×(DR1/DR2)<(HB1/HB2)<1.15×(DR1/DR2) (10)
Note that in the present configuration example, like the first embodiment or the third embodiment, DR1/DR2 is equal to or greater than 1.05 and equal to or less than 5.0 and Ms1t1/Ms2t2 is equal to or greater than 0.25 and equal to or less than 4.0. The reason for this is the same as described in the first embodiment, and thus the description is omitted.
The reason why the size of the base line shift can be reduced to within 20% by satisfying the expression (10) will be described below.
Next, a specific positional relation between the magnetic domain control layer 450 and the first and second free layers for satisfying the expression (10) will be described.
1.7×(DR1/DR2)<a tan α/a tan β+1<2.3×(DR1/DR2)
a tan α={a tan((tHB/2+to−G1/2)/tr1)+a tan((tHB/2−to+G1/2)/tr1)}
a tan β={a tan((tHB/2+to+G1/2)/tr2)+a tan((tHB/2−to−G1/2)/tr2)} (11)
Here, as illustrated in
The expression (11) can be easily derived by solving the simple simultaneous equations of the expression (12) and the expression (10).
HB
1
/HB
2=0.5×a tan α/a tan β+0.5 (12)
Here, HB1/HB2 is derived by calculating a large number of magnetic domain control fields of different shaped magnetic domain control films by finite element method and the calculated results are illustrated in
The reason why HB1/HB2 is in proportion to a tan α/a tan β will be described using
In the configuration example illustrated in
Another configuration example of the present invention will be described. The present configuration example is used when DR1 is smaller than DR2. Like the configuration of the fifth embodiment, the present configuration example reduces the base line shift caused by the difference between DR1 and DR2 to within 20% by controlling HB1 and HB2. The present configuration example is the same as the configuration of the fifth embodiment except the positional relation between the magnetic domain control film and the magneto-resistive film, and thus the detailed description of the configuration is omitted.
Like the second embodiment or the fourth embodiment, DR1/DR2 is equal to or greater than 0.25 and equal to or less than 0.95 and Ms 1t1/Ms2t2 is equal to or greater than 0.25 and equal to or less than 4.0.
Next, a specific positional relation between the magnetic domain control layer 450 and the first and second free layers for satisfying the expression (10) will be described. When the center of the magnetic domain control layer 450 is located closer to the second free layer than to the first free layer, the present configuration example is configured to satisfy the expression (13).
1.7×(DR2/DR1)<a tan α/a tan β+1<2.3×(DR2/DR1)
a tan α={a tan((tHB/2+to−G1/2)/tr2)+a tan((tHB/2−to+G1/2)/tr2)}
a tan β={a tan((tHB/2+to+G1/2)/tr1)+a tan((tHB/2−to−G1/2)/tr1)} (13)
Like the fifth embodiment, the range of a tan α/a tan β according to DR1/DR2 derived from the expression (13) is as illustrated in
Another configuration example of the present invention will be described below. The present embodiment is different from the configuration of the first embodiment only in the range of Ms1t1/Ms2t2. Therefore, DR1/DR2 is assumed to be equal to or greater than 1.05 and equal to or less than 4.0. Here, the description other than the configuration of the first and second free layers regarding Ms1t1/Ms2t2 is omitted. The present configuration is used when Ms1t1/Ms2t2 is larger than 4.0 or smaller than 0.25 in
Control is made in such a manner that when Ms1t1/Ms2t2 is equal to or greater than 4.0, the following expression (14) is satisfied and when Ms1t1/Ms2t2 is less than 0.25, the expression (15) is satisfied.
0.86×(DR1/DR2)<(HB1/HB2)×1/(0.003×((Ms1t1)/(Ms2t2))2+0.997)<1.15×(DR1/DR2) (14)
0.86×(DR2/DR1)<(HB2/HB1)×1/(0.003×((Ms2t2)/(Ms1t1))2+0.997)<1.15×(DR2/DR1) (15)
As the present configuration example,
Another embodiment of the present invention will be described below. The present embodiment is different in configuration from the seventh embodiment only in that the range of DR1/DR2 is equal to or greater than 0.25 and equal to or less than 0.95. Here, the description other than the configuration of the first and second free layers regarding Ms1t1/Ms2t2 is omitted. Like the seventh embodiment, the present configuration example controls such that when Ms1t1/Ms2t2 is equal to or greater than 4.0, the expression (14) is satisfied, and when Ms1t1/Ms2t2 is less than 0.25, the expression (15) is satisfied. As the present configuration example,
Another embodiment of the present invention will be described below. The present embodiment is different in configuration from the first embodiment only in that the saturation magnetization is different between a region contacting the first free layer of the magnetic domain control layer 450 and a region contacting the second free layer thereof. Here, the description other than the configuration regarding the saturation magnetization of the magnetic domain control layer 450 is omitted. In order to control HB1/HB2, the present configuration example controls MsHB1/MsHB2 which is a ratio between the saturation magnetization MsHB1 of the magnetic domain control layer 450 of a region close to the first free layer and the saturation magnetization MsHB2 of the magnetic domain control layer 450 of a region close to the second free layer. More specifically, the differential read head is configured so as to satisfy the following expression (16).
0.86×(DR1/DR2)<(MsHB1/MsHB2)<1.15×(DR1/DR2) (16)
Next, a specific control method for MsHB1 and MsHB2 will be described. The easiest method of controlling MsHB1 and MsHB2 independently is to change the material of the magnetic domain control layer 450 of a region close to the individual magneto-resistive sensors. This is because the saturation magnetization of the magnetic domain control layer 450 depends greatly on the material thereof. Example materials for the magnetic domain control layer 450 include CoCrPt alloy thin film (about 1000 gausses), Fe—Cr—Co alloy (about 13000 gausses), PtCo alloy (about 7000 gausses), and Sm—Co alloy (about 8000 to 10000 gausses).
Any material can be selected from the above typical magnetic materials so as to satisfy the expression (16). The control method for the saturation magnetization of the magnetic domain control layer 450 may include another method of controlling film formation conditions. Any control method for the saturation magnetization may be used as long as the control method is not regarded as a departure from the spirit and scope of the present invention. For example, the method of controlling the film formation conditions includes a method of increasing only the saturation magnetization of the lower magnetic domain control layer 450 by performing thermal treatment only before film formation of the upper film of the magnetic domain control layer 450; and a method of controlling the saturation magnetization by changing the underlying layer of the lower and upper magnetic domain control layers 450.
Another embodiment of the present invention will be described below. The present embodiment is different in configuration from the ninth embodiment only in that the range of DR1/DR2 is equal to or greater than 0.25 and equal to or less than 0.95. Like the ninth embodiment, the present configuration example controls so as to satisfy the expression (16).
Another configuration example of the present invention will be described below. The present embodiment is different from the configuration of the first embodiment only in that the current conducting direction is not a direction perpendicular to the surface of the laminated film 400, but the in-plane direction of the laminated film 400. Here, the description other than the current conducting direction is omitted.
A typical configuration example according to the present invention is illustrated in
According to DR1/DR2 which is a ratio between DR1 and DR2, HB1/HB2 which is a ratio between the magnetic domain control field HB1 applied to the first magneto-resistive sensor 200 and the magnetic domain control field HB2 applied to the second magneto-resistive sensor 300 is configured to satisfy the expression (2) or the expression (5). Note that it is assumed that Ms 1t1/Ms2t2 which is a ratio between the product Ms1t1 of the saturation magnetization Ms1 of the first free layer and the film thickness t1 and the product Ms2t2 of the saturation magnetization Ms2 of the second free layer and the film thickness t2 is equal to or greater than 0.25 and equal to or less than 4.0. Even if the individual magneto-resistive sensors have a different DR, the differential read head of the present configuration example can reduce the size of the base line shift and can suppress the deterioration of the bit error rate.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-151224 | Jun 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/059158 | 5/19/2009 | WO | 00 | 3/30/2011 |
