JP4504928B2 - Method for evaluating characteristics of write element of thin film magnetic head - Google Patents

Description

  The present invention relates to a method of evaluating the characteristics of a write element of a thin film magnetic head, and more particularly to a method of measuring the sharpness of magnetization transition.

  The surface recording density of hard disk devices has been improved year by year. However, since it is becoming difficult to improve the performance of the writing element, it is gradually difficult to improve the surface recording density. One of the causes is the characteristic evaluation method of the writing element.

  FIG. 8 is a schematic diagram showing a range in which magnetization information is recorded in a recording medium of the hard disk device. Magnetization information is recorded for each bit on a plurality of concentric tracks. Ideally, the magnetization range of each bit has a rectangular shape corresponding to the magnetization range 101 in FIG. At this time, the edges E1a and E1b of the magnetization range 101 in the track width direction have a linear shape. However, due to the characteristics of the write element, the magnetization range does not become linear, but edges E2a and E2b whose periphery is distorted as in the magnetization range 102 in FIG. When magnetized in the shape of the edges E2a and E2b, the recording magnetization does not change stepwise in the track width direction (see B in the figure) as shown in FIG. Become. On the other hand, when the ideal edges E1a and E1b are formed, the signal waveform becomes sharp (see A in the figure). In particular, as the arrangement pitch (TPI) of the track in the radial direction of the medium increases as in recent years and the track width decreases, the influence of edge distortion in the track width direction relatively increases and noise further increases. To do. For these reasons, there is an increasing need to more accurately evaluate the shape of the magnetization range of each bit, the track width, and the like recorded by the writing element.

  As a technique which has been conventionally used as such a technique, there is a method using an MFM (magnetic force microscope) (see Patent Document 1). According to this technique, a signal is first recorded on a recording medium using a recording head. Next, the recorded signal pattern is reproduced using MFM. Next, the track width is measured for the reproduced pattern. By using MFM, magnetic recording can be visualized.

The track width can also be measured using a so-called DP test (see Patent Document 2). According to this technique, while scanning the MR head in the radial direction of the recording medium, the test data written on the recording medium is read at a predetermined measurement pitch, and the output voltage is plotted as a function of the radial direction. As a result, an off-track profile curve is generated, and the effective track width (radial range in which the output voltage is equal to or greater than half the maximum output voltage) is calculated.
Japanese Patent Laid-Open No. 11-16164 Japanese Patent Laid-Open No. 10-97711 JP-A-6-223339

  However, the method using MFM is no longer practical due to the limitation of the resolution of MFM, and will become more difficult to apply as TPI increases in the future. The DP test is effective for calculating the effective track width, but is not effective for estimating the edge shape. As described above, in spite of the need to measure the shape of the edge, an effective method has not been developed.

  In view of the above situation, an object of the present invention is to provide a method for evaluating the characteristics of a write element of a thin film magnetic head. In particular, an object of the present invention is to provide a technique capable of more accurately evaluating the shape of an edge facing the width direction of a track in the magnetization range of a recording medium.

In the method for evaluating characteristics of a write element of a thin film magnetic head according to the present invention, an isolated reproduction wave is applied as an input signal to the write element of the thin film magnetic head, and magnetization information corresponding to the isolated reproduction wave is recorded on a predetermined track of the recording medium. A thin film magnetic head having a recording step and a reading element is used to scan a range including a predetermined track of the recording medium in a direction across the width of the track, so that the magnetization information recorded by the writing element is recorded at each scanning position . A step of measuring the signal output and a predetermined harmonic component and a primary component are extracted from the signal output of the magnetization information, and a ratio of the predetermined harmonic component to the primary component in the signal output is calculated as a function of the scanning position. A harmonic component ratio calculating step.

  Since the isolated reproduction wave is given as an input signal to the writing element, the signal output read from a predetermined track on which magnetic information by the isolated reproduction wave is recorded is essentially rectangular regardless of the position in the track width direction. It should be. However, due to the recording characteristics of the writing element, the rectangular shape generally tends to be more easily collapsed near the edge in the track width direction. On the other hand, the rectangular wave has a property that the harmonic component is more excellent than the primary component. Therefore, by calculating the signal output of the magnetization information as a ratio of a predetermined harmonic component to the primary component for each scanning position, it is possible to know how close the shape of the signal output near the edge is to a rectangle. it can.

  Desirably, the predetermined harmonic component is selected from the 5th and 11th order components. In particular, the seventh-order component is suitable as the predetermined harmonic component.

  In the harmonic component ratio calculating step, a predetermined harmonic component and a primary component may be extracted from the output of the measured isolated reproduction wave by a notch filter.

  The recording step may include recording the solitary reproduction wave on different tracks of a single recording medium or on a plurality of recording media with different write currents.

  The recording step may include recording the solitary reproduction wave with different skew angles on different tracks or a plurality of recording media of one recording medium.

  As described above, according to the present invention, the shape of the edge facing the width direction of the track can be more accurately evaluated. For this reason, even if the TPI increases and the track width decreases, the characteristics of the write element of the thin film magnetic head can be more accurately evaluated, which can contribute to further improvement of the performance of the write element. Become.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention can be implemented using a conventionally used spinstand. FIG. 1 shows an example of a spin stand used in this embodiment. The spin stand 1 includes a base 2 as a support base for the apparatus. The recording medium 3 that is a magnetic disk is rotated at an arbitrary number of rotations by a spindle motor (not shown) provided on the base 2. The spinstand 1 also includes a thin film magnetic head 4 that records and reproduces magnetic information on the recording medium 3. The thin film magnetic head 4 is supported by a carriage 5, and the rotary stage 6 on which the carriage 5 is mounted rotates to scan the recording medium 3 in a direction across a predetermined width of the measurement track T. The rotary stage 6 is mounted on a linear stage 7 that moves in parallel, and the distance between the rotation center of the recording medium 3 and the rotation center of the carriage 5 can be changed. Connected to the thin-film magnetic head 4 is a processing device 9 equipped with a notch filter described later, a display for displaying the result, a memory, a CPU, and the like. Further, although not shown, a load / unload mechanism for loading and unloading the thin film magnetic head 4 from the recording medium 3 is provided. The spin stand itself is not particularly limited as long as it is a tester capable of performing a general DP test, and the above-described notch filter and the like need only be added as necessary.

  Next, a method for evaluating the characteristics of the write element of the thin film magnetic head using the present spin stand will be described. FIG. 2 is a flowchart of the characteristic evaluation method described below.

  (Step S1) First, magnetic information is recorded on the recording medium 3 by the writing element of the thin film magnetic head 4 (recording step). Specifically, an isolated reproduction wave is given as an input signal to the writing element of the thin film magnetic head 4, and magnetization information corresponding to the isolated reproduction wave is recorded on the measurement track T of the recording medium. By applying a rectangular wave having a sufficiently low frequency as an input current to the write element, a large number of magnetization ranges having the same shape and the same pitch are formed in the circumferential direction to the extent that the influence of magnetism from adjacent bits can be ignored. In order to suppress the influence of residual magnetic information from the measurement track T and its peripheral tracks, it is preferable to erase (erase) the magnetic information of these tracks before writing.

  (Step S2) Next, the magnetic information recorded on the recording medium 3 is measured using the above-mentioned isolated reproduction wave while scanning the measurement track T in the direction across the track width. Specifically, the signal output of the measurement track T is acquired including the front and rear regions in the track width direction while passing a sense current through the reading element of the thin film magnetic head 4. FIG. 3 is a conceptual diagram showing a scanning method. The reading element of the thin-film magnetic head 4 is sequentially scanned at a predetermined scanning position from the radial position R1 on the inner circumference side of the measurement track T to the radial position Rn on the outer circumference side, and the signal voltage at each radial position. Measure.

  (Step S3) Next, predetermined harmonic components and primary components are extracted from the acquired signal output. Specifically, a notch filter that is a bandpass filter that passes only frequency components of a predetermined bandwidth is used. Alternatively, the acquired signal output may be Fourier transformed. The predetermined harmonic component is preferably a 5th order or more and 11th order or less, and particularly preferably a 7th order component. The reason will be described later.

  (Step S4) Next, the ratio of the acquired signal output to the primary component of the predetermined harmonic component (hereinafter referred to as transition quality) is calculated as a function of the scanning position (harmonic component ratio calculating step). If the graph is drawn with the horizontal axis as the scanning position and the vertical axis as the transition quality, the subsequent analysis and evaluation are easy.

  (Embodiment) Next, a method for evaluating the characteristics of the write element of the thin film magnetic head of the present invention will be described in more detail based on the embodiment. As the writing element, a general inductive electromagnetic transducer having a tip width of about 0.09 μm was used. The tester used was a single arm tester manufactured by Canon-Gdig. Texas Instruments TI1972 was used for the preamplifier. The measurement was performed at the outer periphery of the recording medium (radius 44.14 mm, skew angle 16.0 degrees, writing frequency 535.3 MHz). Considering the write current, write current overshoot, and overshoot duration as parameters, multiple combinations were implemented. Here, overshoot refers to passing a current exceeding the original write current when writing magnetic recording near the edge in order to intentionally create linearity (sharpness) near the edge of the magnetization range.

  FIG. 4 shows the result of plotting the output voltage of the primary component. The reason for the multiple lines is that multiple cases with different combinations of write current, write current overshoot, and overshoot duration were implemented. From these figures, it can be seen that a mountain-shaped distribution centered around the center of the graph is obtained. FIG. 5 shows the result of plotting the output voltage of the seventh-order component. Similarly, although a mountain-shaped distribution centered around the center of the graph is obtained, it can be seen that the output voltage value is small overall and the variation in each case is large.

  FIG. 6 is a plot of transition quality with the horizontal axis as the scan position in the track width direction. The two minimum value regions A1 and A2 substantially correspond to both ends of the magnetization range of the track. A maximum value region B between the minimum value regions A1 and A2 substantially corresponds to the center of the magnetization range of the track.

  Here, the meaning of the shape of the graph is considered as follows. When the magnetization range is obtained in a beautiful rectangular shape as shown in FIG. 8A, the signal output at each position in the track width direction is also a beautiful rectangular shape. As a general property when the rectangular wave is Fourier-expanded, the harmonic component appears more prominently as the signal output is closer to the rectangular shape, and the primary wave component is relatively reduced. Therefore, it can be estimated that the higher the transition quality, the closer the signal output is to a rectangle, and the smaller the value, the farther away from the rectangle, that is, the magnetization range is distorted.

  Since the local maximum region B corresponds to the substantially central position C in the track width direction of the track T to be measured (see FIG. 8B), the influence of the edges E2a and E2b in the track width direction (see FIG. 8B). And the rectangular shape is most easily maintained. For this reason, harmonic components appear outstandingly, and the transition quality becomes a maximum value. On the other hand, the minimum value areas A1 and A2 correspond to substantially both ends of the measurement target track T in the track width direction, that is, the positions of the edges E2a and E2b in the track width direction. Since the rectangular shape of the signal output along the edges E2a and E2b is most easily collapsed, the harmonic component is relatively attenuated, and the transition quality becomes the minimum value. Therefore, by comparing the absolute values of the minimum value regions A1 and A2, it is possible to estimate whether the sharpness of the edges E2a and E2b in the track width direction, that is, whether the magnetization range is formed closer to a rectangle. Alternatively, whether or not the magnetization range is close to a rectangle can also be estimated by determining the ratio of the transition quality in the minimum value regions A1 and A2 to the transition quality in the maximum value region B. In addition, the width of the magnetization range, that is, the track width can be measured from the interval between the minimum value regions A1 and A2.

  The fifth to eleventh order components are used as the harmonic components because the signal output becomes small and the signal-to-noise ratio deteriorates when the component is too high, whereas the sharpness of the edge appears as a numerical value when the component is the fourth or lower. This is because it is difficult. The 7th order wave is the middle of the 5th to 11th orders, and is balanced and optimal.

  In some cases, a second maximum value region C appears between the maximum value region B and the minimum value region A2. This indicates that the signal output does not transition smoothly with the scanning position. That is, it means that some irregular magnetization pattern exists in the vicinity of the second maximum value region C. In this embodiment, the write current is increased little by little in the range of 21 mA to 45 mA. In FIG. 6, the second maximum value region C appeared in the two cases with the largest write current. Thus, if a plurality of recording media are used to record magnetic recording with different write currents and the same test is performed, these characteristics appear more clearly and the reliability of the test can be improved. Of course, at this time, the same result can be obtained even when magnetic recording is recorded on different tracks of one recording medium with different write currents.

  Next, a similar test was performed using the skew angle as a parameter. In order to change the skew angle, in addition to the outer peripheral portion of the recording medium described above, the inner peripheral portion (radius 19.21 mm, skew angle −9.03 degrees, writing frequency 271.9 MHz), near the center (radius 28.87 mm, skew) A similar test was performed at an angle of 3.23 degrees and a writing frequency of 381.6 MHz. Here, the skew angle is an angle difference between the tangential direction of the track at the position where the magnetic head is present and the axial direction of the magnetic head (see symbol s in FIG. 1). FIG. 7 shows the transition quality of each case (the vertical axis is indicated as TQ). From this, it can be seen that the maximum value region C2 appears in the measurement at the outer peripheral portion having a large skew angle. Therefore, it is considered effective to effectively carry out the present invention to record magnetic recording on different tracks of a recording medium or on a plurality of recording media with mutually different skew angles.

It is a schematic block diagram of the spin stand used in this embodiment. It is a flowchart of the write element characteristic evaluation method of the thin film magnetic head by this invention. It is a conceptual diagram which shows the scanning method. It is a graph which shows the result of having plotted the output voltage of the primary component. It is a graph which shows the result of having plotted the output voltage of the 7th-order component. It is a graph which shows the result of having plotted transition quality. It is a comparison figure of transition quality using skew angle as a parameter. It is a schematic diagram which shows the range in which the magnetization information is recorded in the recording medium of a hard disk device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Spin stand 3 Recording medium 4 Thin film magnetic head A1, A2 Local minimum area B Local maximum area C Second local maximum area C2 Local maximum area E2a, E2b, E1a, E1b Edge R1-Rn Radial position T Measurement track

Claims (6)

A recording step of applying an isolated reproduction wave as an input signal to the writing element of the thin film magnetic head and recording magnetization information corresponding to the isolated reproduction wave on a predetermined track of the recording medium;
The magnetization information recorded by the writing element at each scanning position by scanning a range including the predetermined track of the recording medium in a direction across the width of the track with a thin film magnetic head having a reading element. Measuring the signal output of
The removed and the predetermined harmonic component from the signal output and the first-order component of the magnetic information, the ratio of the primary component of the predetermined harmonic component in the signal output, harmonics calculated as a function of the scan position A component ratio calculating step;
A method for evaluating characteristics of a write element of a thin film magnetic head, comprising:   The characteristic evaluation method according to claim 1, wherein the predetermined harmonic component is a component of 5th order or more and 11th order or less.   The characteristic evaluation method according to claim 2, wherein the predetermined harmonic component is a seventh-order component.   The harmonic component ratio calculating step includes extracting the predetermined harmonic component and the first-order component from the measured output of the isolated reproduction wave by a notch filter. The characteristic evaluation method according to any one of the above items.   5. The recording step according to claim 1, wherein the recording step includes recording the isolated reproduction wave on a different track or a plurality of recording media of one recording medium with a writing current having a different magnitude. The property evaluation method described in 1.   5. The recording method according to claim 1, wherein the recording step includes recording the solitary reproduction wave on different tracks of a single recording medium or on a plurality of recording media with mutually different skew angles. 6. Characterization method.

Images