JP2004005838A - Perpendicular magnetic disk unit - Google Patents

Abstract

Provided is a perpendicular magnetic disk device that avoids a non-linear response of a GMR element and does not deteriorate error rate.
A perpendicular magnetic recording medium having a perpendicular recording layer, and a reproducing head including a magnetoresistive element for reading out magnetization recorded on the perpendicular magnetic recording medium, wherein between the reproducing head and the recording layer. The magnetic spacing S (nm) of the following equation is 0.0532L + 32.65>S> 0.0532L + 2.65
(Where L is the longest bit length (nm))
Perpendicular magnetic disk drive that meets the requirements.
[Selection] Fig. 2

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a perpendicular magnetic disk drive.
[0002]
[Prior art]
Magnetic disk drives continue to dramatically increase recording density. This is largely due to user needs for large capacity and miniaturization, and this trend is expected to continue in the future.
[0003]
The recording density improving technology includes a technology relating to the recording / reproducing ability of each of the head and the medium, and a technology relating to performance as a magnetic disk device. The miniaturization of the magnetic particles constituting the recording layer in the current longitudinal recording medium is also an important technique that greatly contributes to the improvement of the recording density. That is, when the magnetic particles are miniaturized, the width of the magnetization transition can be narrowed, and high-resolution reproduction can be performed, which contributes to higher density. However, when the magnetic particles are miniaturized, the influence of thermal fluctuation becomes large, and there is a possibility that the recording magnetization disappears. Therefore, it is difficult to further miniaturize the recording particles. This is considered to be the limit of the longitudinal recording medium, and a new technique for overcoming this is required.
[0004]
Perpendicular recording is one of the technologies that exceeds the limit of longitudinal recording media. In the perpendicular recording method, since the recording magnetization direction is different from that in the longitudinal recording method, there is theoretically no recording density limit due to thermal fluctuation, and a higher recording density can be realized than in the longitudinal recording method. Further, there is an advantage that the magnetization transition width is narrow and a large output is obtained as a differential waveform at the steep magnetization transition. For this reason, it is expected that magnetic disk devices in the future will adopt the perpendicular recording method. Here, also in the perpendicular magnetic disk device, it is assumed that a magnetoresistive element such as a giant magnetoresistive element (GMR element) is used for the reproducing head as in the longitudinal recording type.
[0005]
However, it has been found that in a perpendicular magnetic disk drive using a reproducing head including a GMR element, a problem of deterioration of an error rate accompanying non-linear reproduction occurs. Hereinafter, this point will be described.
[0006]
The GMR element has a laminated structure including an antiferromagnetic layer, a soft magnetic layer (pin layer), a non-magnetic layer, and a soft magnetic layer (free layer), depending on whether the magnetization of the pin layer and the free layer is parallel or antiparallel. By utilizing the fact that the electrical resistance changes (GMR effect), the reproducing magnetic field is detected by the change in the resistance value.
[0007]
On the other hand, as a magnetic disk of a perpendicular magnetic disk device, a magnetic disk in which a soft magnetic underlayer and a perpendicular recording layer are laminated is generally used. When reproducing the recorded magnetization of such a magnetic disk, magnetic coupling occurs between the GMR element and the soft magnetic underlayer. For this reason, the perpendicular recording method can obtain a high reproduction magnetic field and a high reproduction output, which are about twice that of the longitudinal recording method, and are considered to be advantages over the longitudinal recording method.
[0008]
However, since the magnetization of the free layer of the GMR element is finite, if the reproducing magnetic field is too large, the response of the free layer becomes dull or unresponsive. This is called non-linear reproduction. In addition, as the dimensions of the GMR element become smaller, a reproduction nonlinear response is more likely to occur. When a non-linear response occurs, a reproduced waveform is distorted, and optimal signal processing cannot be performed in a channel, thereby causing a deterioration in an error rate. Thus, in the GMR element for converting the reproducing magnetic field (H) into the reproducing output (ρ), it is apparent that the ρ-H characteristic desirably has a linear relationship.
[0009]
Since the reproducing magnetic field is small in the longitudinal magnetic disk device, nonlinear reproduction has not been a problem so far. That is, the above problem is a problem peculiar to a perpendicular magnetic disk device having a large reproducing magnetic field. On the other hand, when focusing on the reproducing element, the above problem is a common problem that occurs not only in the GMR element but also in the tunnel magnetoresistive element (TMR element).
[0010]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a perpendicular magnetic disk drive which avoids a non-linear response of a GMR element and does not cause an error rate degradation.
[0011]
[Means for Solving the Problems]
A magnetic disk drive according to one aspect of the present invention includes a perpendicular magnetic recording medium having a perpendicular recording layer, and a read head including a magnetoresistive element for reading magnetization recorded on the perpendicular magnetic recording medium, and The magnetic spacing S (nm) between the head and the recording layer is expressed by the following equation: 0.0532L + 32.65>S> 0.0532L + 2.65
(Where L is the longest bit length (nm))
Is satisfied.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail.
In order to prevent non-linear reproduction from occurring in the perpendicular magnetic disk device, it is conceivable to increase the linear region of the reproduction output (ρ) of the GMR element with respect to the reproduction magnetic field (H) or reduce the reproduction magnetic field. As the former approach of expanding the linear region, it is conceivable to (1) moderate the slope of the ρ-H characteristic. The latter approach for reducing the reproducing magnetic field includes: (2) adjusting the position, shape, and material of the reproducing shield constituting the reproducing head to increase the reproducing magnetic field introduced into the reproducing shield; and (3) between the reproducing head and the medium. And (4) reducing the residual magnetization of the medium.
[0013]
Here, in the development process of the magnetic disk device so far, there has been a tendency to reduce the flying height of the magnetic head in order to cope with a decrease in the reproducing magnetic field and a decrease in the resolution accompanying the improvement in the recording density. For this reason, the perpendicular magnetic disk device is also designed to have a flying height as low as possible by adopting a design adapted to a region where the reproduction output in the longitudinal recording method is low. On the other hand, if the flying height is increased in the perpendicular magnetic disk drive, the magnetic field between the read head and the medium in (3) can be increased to reduce the read magnetic field, and the reliability and manufacturability of the drive can be improved. So desirable.
[0014]
In the present invention, as described above, the magnetic spacing S (nm) is
S> 0.0532L + 2.65
(Where L is the longest bit length (nm))
Wide to meet. However, if the magnetic spacing is too wide, the bit error rate (BER) deteriorates.
0.0532L + 32.65> S
The upper limit of the magnetic spacing S is set so as to satisfy the following. The derivation of these equations will be described in detail in the section of Examples.
[0015]
In addition, as a known example which regulates a magnetic spacing between a magnetic head and a perpendicular recording layer in a perpendicular magnetic disk device, there are Japanese Patent No. 3039033 and Japanese Patent Laid-Open No. 6-267221.
[0016]
Japanese Patent No. 3039033 discloses a technique for reducing fluctuations in reproduction output with respect to minute fluctuations in spacing between a leading end face of a main pole of a single pole type magnetic head and a perpendicular recording film surface of a perpendicular magnetic recording medium having a two-layer film structure. It discloses that the spacing is appropriately set for stabilization. From the expression described in the claims of this publication, it is understood that the upper limit value of the spacing is set according to the characteristics of the perpendicular recording film.
[0017]
JP-A-6-267221 discloses that the spacing between the medium and the head at the time of recording is made smaller than the spacing between the medium and the head at the time of reproduction in order to avoid a decrease in the reproduction output of the perpendicular recording medium. are doing. Also, in this publication, an upper limit value is specified for the spacing between the medium and the head during reproduction.
[0018]
However, none of the above known examples disclose the problem of avoiding non-linear reproduction, and in order to solve this problem, the present invention of increasing the magnetic spacing between the medium and the reproduction head as compared with the conventional apparatus. Does not suggest the technical idea.
[0019]
A perpendicular magnetic recording medium used in a magnetic disk device according to an embodiment of the present invention has a soft magnetic underlayer and a perpendicular recording layer formed on a substrate. Note that an underlayer such as a crystal control layer may be provided between the soft magnetic underlayer and the perpendicular recording layer. Usually, a protective layer is provided on the perpendicular recording layer.
[0020]
The soft magnetic underlayer is desirably a material having both high magnetic permeability and high saturation magnetic flux density. As the material of the soft magnetic underlayer, a material containing a 3d transition metal such as Fe or Co is used, and specific examples thereof include CoZrNb and FeAlSi.
[0021]
The perpendicular recording layer is preferably made of a material having perpendicular magnetic anisotropy and satisfying low coercive force, high remanence magnetization and high squareness ratio. If the coercive force is too high, good recording may not be possible depending on the capability of the recording head. In consideration of the recording performance of the current recording head, the coercive force of the perpendicular recording layer is desirably about 3 to 6 kOe. The perpendicular recording layer desirably has a high remanent magnetization for a high reproduction output and a high squareness ratio for a high recording holding ability. Specific examples of the material of the perpendicular recording layer include a CoCr-based alloy and an artificial lattice film in which Co layers and nonmagnetic layers are alternately stacked.
[0022]
The reproducing head used in the magnetic disk drive of the embodiment of the present invention includes a magnetoresistive element as a reproducing element. Specific examples of the magnetoresistive element include a giant magnetoresistive element (GMR element) and a tunnel magnetoresistive element (TMR element) that can realize high-sensitivity reproduction.
[0023]
The GMR element has a laminated structure including an antiferromagnetic layer, a soft magnetic layer (pin layer), a metal non-magnetic layer, and a soft magnetic layer (free layer). The TMR element has a laminated structure including an antiferromagnetic layer, a soft magnetic layer (pin layer), a dielectric layer, and a soft magnetic layer (free layer). Usually, these reproducing elements are sandwiched between a pair of shields.
[0024]
The reproducing head is formed together with the recording head. A typical example of the recording head is a single pole head suitable for perpendicular magnetic recording. The magnetic pole material is desirably a material that satisfies high magnetic permeability and high saturation magnetic flux density, and specific examples include permalloy. The magnetic pole shape is desirably machined so that the ABS surface becomes trapezoidal in order to reduce the magnetization transition width.
[0025]
The read signal read by the read head is subjected to signal processing in a channel including a differentiating circuit and is converted into a differential signal.
[0026]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0027]
FIG. 1 is a perspective view showing the internal structure of the perpendicular magnetic disk drive in this embodiment. A magnetic disk 10 is rotatably mounted on a spindle motor 11 in the housing 1. On the other hand, an arm 13, a suspension 14, and a slider 15 are attached to a shaft 12 near the magnetic disk 10, and a magnetic head (not shown in FIG. 1) including a reproducing head and a recording head is formed at the tip of the slider 15. . The arm 13 is movable in the radial direction of the magnetic disk 10 by a voice coil motor 16. At the time of recording / reproducing, a magnetic head including a reproducing head and a recording head is arranged on a predetermined track formed on the surface of the magnetic disk 10 in a floating state. The magnetic head is connected to a circuit board on which a preamplifier circuit, a read / write channel, a controller and the like are mounted via a flexible printed circuit.
[0028]
FIG. 2 is a sectional view showing the magnetic disk and the magnetic head during recording / reproduction. The magnetic disk 10 has a structure in which a soft magnetic underlayer 102, a crystal control layer 103, a perpendicular recording layer 104, and a protective layer 105 are formed on a nonmagnetic substrate 101. On the vertical recording layer 104, the longest bit length L is displayed.
[0029]
The magnetic head 20 includes a reproducing head 21 and a recording head 22. The reproducing head 21 has a structure in which a GMR element 202 is interposed between a pair of shields 201 and 203 via an insulating layer on a head substrate (not shown). GMR element 202 includes an antiferromagnetic layer, a pinned layer, a metal nonmagnetic layer, and a free layer. A single pole head 204 is formed on one shield 203 via an insulating film. The single pole head 204 is magnetically coupled to the shield 203 at a position retracted from the medium facing surface. An exciting coil (not shown) is embedded in an insulating film between the shield 203 and the single pole head 204. A protective layer 205 is formed on the entire surface of the magnetic head 20.
[0030]
FIG. 2 shows the flying height FH of the magnetic head and the magnetic spacing S between the head and the recording layer.
[0031]
The recording magnetic field generated from the single pole head 204 forms a closed magnetic path through the perpendicular recording layer 104 and the soft magnetic underlayer 102, and a recording magnetic field is applied to the perpendicular recording layer 104 in a direction perpendicular to the film surface. The read signal read by the GMR element 202 is converted into a differentiated signal through a channel including a differentiating circuit and subjected to signal processing.
[0032]
FIG. 3 shows a relationship (ρ-H characteristic) between the reproduction output TAA (μV) of the GMR element and the reproduction magnetic field. This figure examines the characteristics of the GMR element alone. The same measurement was performed for the five GMR elements. In each case, the same tendency was shown, and FIG. 3 shows a representative example.
[0033]
As shown in FIG. 3, the GMR element can be considered to have a linear response when the reproducing magnetic field is in a range from about -250 Oe to about 200 Oe. However, when the reproducing magnetic field exceeds about -250 Oe or about 200 Oe, the reproducing output of the GMR element is saturated and the slope becomes gentle. Here, the limit of the linear region is defined as Hs. From FIG. 3, it can be seen that this magnetic head has a reproduction output of 1600 μV (H = 200 Oe) or more and performs reproduction using the nonlinear region of the ρ-H characteristic (non-linear reproduction).
[0034]
When nonlinear reproduction is performed, the signal is distorted, which causes an increase in error rate during signal processing in a channel. Hereinafter, in order to prevent this problem in the present invention, a means for performing linear reproduction without using a nonlinear region of the ρ-H characteristic will be described.
[0035]
FIG. 4 shows the dependence of the reproduction output on the recording frequency in the perpendicular magnetic disk device of this embodiment. As shown in FIG. 4, when the recording frequency is increased, the reproduction output decreases. For this reason, it can be understood that it is sufficient to consider a condition that non-linear reproduction is not performed when reproducing a signal having the lowest recording frequency at which a large reproduction output is obtained.
[0036]
FIG. 5 shows an enlarged view of the low recording frequency region of FIG. 4 in order to examine the reproduction output at the lowest recording frequency in detail. From FIG. 5, the relationship between the reproduction output TAA (μV) at a low recording frequency and the recording frequency f (kFCI) is as follows.
TAA = -1.62f + 1750
It can be seen that a linear approximation can be made.
[0037]
The recording frequency on the horizontal axis in FIG. 5 is converted into the longest bit length L, and the relationship between the reproduction output TAA (μV) and the longest bit length L (nm) is shown in FIG. From FIG. 6, the relationship between the reproduction output TAA (μV) and the longest bit length L (nm) is as follows.
TAA = 0.159 L + 1577
It can be seen that can be linearly approximated by
[0038]
By substituting TAA = 1600 μV, which is the limit of the linear region obtained in FIG. 3, into the above equation, it can be seen that non-linear reproduction is performed with recording bits longer than 145 nm. Therefore, if the reproduction output can be reduced by (L-145) × 0.159 (μV), it can be said that the non-linear reproduction is eliminated.
[0039]
Here, it is considered that the reproduction output is reduced by widening the magnetic spacing S to eliminate nonlinear reproduction.
[0040]
FIG. 7 shows the relationship between the increment ΔS of the magnetic spacing S and the normalized reproduction output. FIG. 7 shows that increasing the magnetic spacing by 1 nm reduces the reproduction output by 1%. In the magnetic head of the present embodiment, since the reproduction output of 1% corresponds to 17.5 μV, the increment ΔS of the magnetic spacing to be increased to suppress the head saturation is ΔS = (L−145) × 0.159) / 17 .5
It becomes.
[0041]
FIG. 8 shows the relationship between the magnetic spacing Sc and the longest bit length L in the current design. The relationship of the broken line in FIG.
Sc = 0.0441L + 3.964
It becomes. However, non-linear regeneration occurs in this design. For this reason, in the present invention, the magnetic spacing S is made wider than the current Sc by at least ΔS. That is, magnetic spacing S> (Sc + ΔS). By substituting the above Sc and ΔS into this equation, the relationship between the magnetic spacing S and the longest bit length L in the present invention can be obtained. That is,
S> 0.0532L + 2.65
(Where L is the longest bit length (nm))
This equation is shown by a solid line in FIG. If the magnetic spacing S is designed so as to satisfy this equation, nonlinear reproduction can be eliminated.
[0042]
Next, the upper limit of the magnetic spacing S will be discussed. FIG. 9 shows the flying height (ΔFH) dependency of the bit error rate (BER) of the perpendicular magnetic disk drive. As shown in FIG. 9, when the flying height increases by 1 nm, the BER deteriorates by about 0.1. As can be seen from this figure, if the flying height is increased more than necessary, the BER deteriorates and the HDD performance does not meet the specifications. The BER initial value of the HDD is about 6.0, and if this value is close to 3.0, the BER improvement is significantly deteriorated even if signal processing is performed thereafter. Therefore, when the BER degradation becomes 3.0 or more, the demerit is clearly large. This value corresponds to a ΔFH of 30 nm. Therefore, in the present invention, the upper limit of the magnetic spacing S (nm) is
0.0532L + 32.65> S
(Where L is the longest bit length (nm))
It is preferable that
[0043]
As described above, in the perpendicular magnetic disk drive designed so that the magnetic spacing satisfies the above expression, the nonlinear reproduction can be eliminated.
[0044]
【The invention's effect】
As described in detail above, according to the present invention, it is possible to provide a perpendicular magnetic disk drive that avoids the non-linear response of the GMR element and does not deteriorate the error rate.
[Brief description of the drawings]
FIG. 1 is a perspective view showing the internal structure of a perpendicular magnetic disk drive according to an embodiment of the present invention.
FIG. 2 is a sectional view showing a magnetic disk and a magnetic head during recording / reproduction.
FIG. 3 is a diagram showing a relationship between a reproduction output TAA of a GMR element and a reproduction magnetic field.
FIG. 4 is a diagram showing the recording frequency dependence of the reproduction output of the perpendicular magnetic disk device according to the embodiment of the present invention.
FIG. 5 is an enlarged view showing a low recording frequency region in FIG. 4;
FIG. 6 is a diagram showing a relationship between a reproduction output TAA and a maximum bit length L.
FIG. 7 is a diagram showing a relationship between an increment ΔS of a magnetic spacing S and a normalized reproduction output.
FIG. 8 is a diagram showing the relationship between the magnetic spacing Sc and the longest bit length L in the current design, and the relationship between the magnetic spacing S and the longest bit length L in the present invention.
FIG. 9 is a diagram showing the flying height dependency of the bit error rate of the perpendicular magnetic disk device in the embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Case 10 ... Magnetic disk 11 ... Spindle motor 12 ... Axis 13 ... Arm 14 ... Suspension 15 ... Slider 16 ... Voice coil motor 20 ... Magnetic head 21 ... Reproduction head 22 ... Recording head 101 ... Non-magnetic substrate 102 ... Soft magnetism Backing layer 103 Crystal control layer 104 Perpendicular recording layer 105 Protective layers 201 and 203 Shield 202 GMR element 204 Single pole head 205 Protective layer

Claims (2)

A perpendicular magnetic recording medium having a perpendicular recording layer; and a reproducing head including a magnetoresistive element for reading magnetization recorded on the perpendicular magnetic recording medium, wherein a magnetic spacing between the reproducing head and the recording layer is provided. S (nm) is the following formula: 0.0532L + 32.65>S> 0.0532L + 2.65
(Where L is the longest bit length (nm))
A perpendicular magnetic disk drive characterized by satisfying the following. 2. The perpendicular magnetic disk drive according to claim 1, wherein the perpendicular recording layer is formed of a CoCr-based alloy.

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