JP2005209274A - How to measure erase bandwidth - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure an erase band width in a short time by reading and writing on a magnetic disk medium by a magnetic head.
After DC erasing around a test track whose erase band width is to be measured, test track recording steps 101 and 102 for recording a periodic signal of a predetermined frequency on the test track, and an erase position adjacent to the test track are determined. While gradually moving to the center of the test track, each erase position is sequentially DC erased, and each time the erase position is DC erased, the residual signal is reproduced at the track edge of the test track and the signal strength of the residual signal is calculated. Erase residual signal measurement steps 103 to 110 for measuring media noise and recording these, and erase band width calculation for calculating the width of the erase band based on the signal strength of the residual signal at each erase position and the measured data of the media noise Steps 111-113 are included.
[Selection] Figure 6

Description

  The present invention relates to an erase band width measuring method for measuring a width of an erase band formed at an end of a track when a signal is recorded on a magnetic disk medium by a magnetic head.

A hard disk device is known as a large-capacity external storage device that reads and writes digital information by floating a magnetic head on a magnetic disk medium that rotates at high speed. In such a hard disk device, the magnetic disk medium is placed on the same spindle shaft. Using one or more stacked ones, an arm equipped with at least one magnetic head corresponding to each surface of the magnetic disk medium is provided, and this is moved in the radial direction to select a target track. Recording and playback.
As a write (recording) head for recording, an inductive head as shown at 20 in FIG. 2 is mainly used. The inductive head has a structure in which a coil 22 is wound around a part of a ring-shaped core 21. A gap 24 is provided at one end of the core 21, and both ends of the gap 24 form a magnetic pole. Recording on the magnetic disk medium 1 is performed using a leakage magnetic field from the gap 24 generated when a write current is passed through the coil 22.

On the other hand, an MR (Magneto Resistive) element (magnetoresistive element) that converts a change in magnetic field into a change in electrical resistivity is generally used for the read (reproducing) head. Further, recently, GMR (Giant Magneto Resistive) elements having a sensitivity twice as high as that of MR elements have been used.
Incidentally, the magnetic field generated from the gap 24 of the write head 20 spreads on both sides of the track due to the edge effect. Since the magnetic field is weaker at the end of the spread, the magnetic disk medium 1 is not saturated and magnetized. Therefore, as shown in FIG. 3, erase bands 31 are formed at both ends of the track 32 on which a signal is recorded. The erase band 31 is a region where magnetic moments are randomly arranged. In other words, media noise is dominant in this area. Media noise is noise based on irregularities and fluctuations in the magnetization transition state.

By the way, when erasing a track on which a signal is recorded, DC (direct current) erase is generally performed. DC erase is a process in which a track is saturated and magnetized in one direction by supplying a relatively large DC current to the write head, and an erase band is not normally formed in a track on which DC erase has been performed.
The width of the erase band is determined mainly by the shape of the recording head (gap width, write width, pole length, etc.) and the characteristics of the magnetic pole material. The width also changes depending on the recording conditions (recording current, recording frequency, etc.). Incidentally, in a recent head having a write width of 200 nm to 300 nm, the width of the erase band is about 10 nm to 20 nm.
Such an erase band increases the total track width, thus limiting the storage capacity per magnetic disk medium. Therefore, in the research and development of heads and disks for increasing the recording density of magnetic disk media, it is important to evaluate the characteristics by measuring the erase bandwidth.

Conventionally, several methods have been used to measure the erase bandwidth. One of them is a method using a magnetic force microscope (MFM). A magnetic force microscope is a device that scans and detects the magnetic properties (magnetic domain state, etc.) of a measurement sample with a probe in a non-contact manner, and images this on a monitor.
Another method is disclosed in Non-Patent Document 1. This method uses a spinstand and a spectrum analyzer. The method first DC erases the periphery of the test track. Next, two reference tracks having the same linear recording density are recorded adjacent to each other by the recording head. Next, test tracks having different linear recording densities are recorded at the centers of the two reference tracks. Next, a track scan is executed around the test track.
At this time, the reproduction signal intensity of the two reference tracks and the test track is measured using a spectrum analyzer, and the respective track profiles are obtained. Further, the erase band width is obtained by data processing of the obtained three track profiles.
JP 2000-339601 A JP 2000-195012 A JP 2002-93088 A "Effects of Current and Frequency on Write, Read, and Erase Widths for Thin-Film Inductive and Magnetoresistive Heads" (IEEE Transactions on Magnetics, Vol. 25, No. 1, January 1989)

However, the above-described MFM method has a problem that it takes time to adjust, measure, and post-process the apparatus, and the method disclosed in Non-Patent Document 1 has an advantage that the measurement time is shorter than the MFM method. Since two reference tracks having different linear recording densities are required in addition to the test track, there is a problem that the processing becomes complicated.
In view of the above points, the present invention enables an erase band that enables measurement in a short time by reading and writing to a magnetic disk medium by a magnetic head, and at that time without requiring an extra reference track. It aims at providing the measuring method of width.

  In order to achieve the above object, the present invention provides an erase band width measuring method for measuring the width of an erase band formed at an end of a track when a signal is recorded on a magnetic disk medium by a magnetic head. A test track recording step of recording a periodic signal of a predetermined frequency on the test track by the magnetic head after DC erasing the periphery of the test track of the magnetic disk medium whose width of the erase band is to be measured; Each erasure position is sequentially DC erased by the magnetic head while gradually moving the erase position adjacent to the test track to the center of the test track, and each time the erase position is DC erased, the test track Play the residual signal at the track edge An erase residual signal measuring step for measuring signal strength and media noise of the residual signal and recording them, and the width of the erase band based on the signal strength and media noise measurement data of the residual signal at each erase position. And an erasing bandwidth calculating step of calculating.

  Here, the erase bandwidth calculating step calculates a first erase position at which the signal strength starts to decrease due to DC erase from the measurement data of the signal strength of the residual signal for each erase position; A step of calculating a second erase position where the media noise starts to decrease due to DC erase from the measured data of the media noise of the residual signal with respect to the erase position, and a difference between the first erase position and the second erase position Preferably, the magnetic head includes a recording head and a reproducing head, and the DC erasing and recording of a periodic signal having a predetermined frequency are performed using the recording head. Preferably, the residual signal is reproduced using the reproducing head.

According to the present invention, the erase band width is measured by reading and writing to the magnetic disk medium by the magnetic head. Therefore, the erase band width can be measured in a short time, and an extra reference track is required. The processing is simple and easy to implement.
Therefore, the characteristic evaluation of the magnetic head and / or magnetic disk medium based on the erase band width can be made efficient and labor-saving.

As an embodiment of the present invention, it is preferable to apply the measurement method of the present invention by mounting a magnetic head and a magnetic disk medium including a recording head and a reproducing head on a read / write test apparatus including a spin stand.
The erase band width (erase band width calculated in the erase band width calculation step) measured according to the present invention indicates a combination characteristic of a magnetic head and a magnetic disk medium mounted on the read / write test apparatus. If the standard one is used for one of the media, the other characteristic is exhibited.

Next, examples of the present invention will be described. FIG. 1 shows a configuration of a read / write test apparatus used in an embodiment of an erase bandwidth measuring method according to the present invention. The read / write test apparatus 9 includes a spin stand 3, a signal generator 6, a spectrum analyzer 7, and a controller 11.
The spin stand 3 includes a spindle motor 8 for rotating the magnetic disk medium 1, a head slider 2 as a magnetic head, a load / unload mechanism 15 for loading / unloading the head slider 2, and the head slider 2 as a magnetic disk. The head positioning mechanism 10 for positioning to an arbitrary track on the medium 1 and a read / write amplifier 14 are configured.
The head slider 2 includes an inductive write head 20 and a read head (not shown) using an MR element.

The read / write amplifier 14 includes a write amplifier (not shown) for generating a write current and a read amplifier (not shown) for amplifying a head signal. The write current output terminal of the read / write amplifier 14 is connected to the coil of the write head 4 via the write current signal line 17. The output of the read head is connected to the amplifier input terminal of the read / write amplifier 14 via the MR signal line 16.
The controller 11 is connected to the spin stand 3, the signal generator 6, and the spectrum analyzer 7 through a communication line 12, and can be remotely controlled by various commands. The controller 11 includes a personal computer, an operating system, and a control program for the read / write test apparatus 9.
Next, the erase bandwidth measurement procedure of this embodiment will be described. FIG. 6 is a flowchart showing a procedure for measuring the erase bandwidth of the embodiment. In this measurement procedure, steps 101 and 102 are the test track recording step of the present invention, steps 103 to 110 are the erase residual signal measurement step of the present invention, and steps 111 to 113 are the erase bandwidth calculation step of the present invention. It is composed.

First, as shown in step 100 of FIG. 6, preparation for measurement is first performed. Therefore, first, the magnetic disk medium 1 is set on the spin stand 3 and rotated at a predetermined rotational speed. When the magnetic disk medium 1 reaches a steady rotation speed (for example, 4500 rpm), the head positioning mechanism 10 moves the head slider 2 to a predetermined load position (for example, the outer peripheral portion of the recording surface of the magnetic disk medium 1). Then, the head slider 2 is lowered onto the recording surface of the magnetic disk medium 1 by the load / unload mechanism 15 and floated. Thus, preparation for measurement is completed.
Next, as shown in step 101 of FIG. 6, the periphery of the test track is DC erased. DC erase is a process of saturation magnetization of the entire track in the same direction. The DC erase can be performed by supplying a DC current of about 50 mA to 60 mA to the coil of the write head 4 for a certain period of time. As a test track, an arbitrary track in the recording surface of the magnetic disk medium 1 can be selected. In this step, not only the test track but also the tracks around this track are collectively DC erased.

Next, as shown in step 102 of FIG. 6, the periodic signal is recorded for one round on the test track. Therefore, first, the write head 4 is moved to the center position of the test track. Next, a square wave signal having a predetermined frequency (for example, 10 MHz) is generated from the signal generator 5. The read / write amplifier 14 converts the square wave signal into a write current whose polarity is inverted at a constant cycle. The write current is supplied to the coil of the write head 4 via the write current signal line 17, and the leakage magnetic field generated from the gap changes the magnetization direction of the track under the gap based on the polarity of the write current. As a result, the data track 32 shown in FIG. 3 and the erase band 31 adjacent thereto are recorded on the magnetic disk medium 1 as test tracks.
Next, as shown in step 103 of FIG. 6, the first erase position is set to the radial position on the inner circumference side of the test track. Here, it is desirable that the first erase position has a sufficient distance from the test track. At least a distance that does not erase the test track (including the erase band) by DC erase is necessary. For example, as indicated by reference numeral 35 in FIG. 4, it is set at a position on the inner circumference side by 1.5 times the recording width of the write head 20 from the center of the test track.

Next, as shown in step 104 of FIG. 6, the write head is moved to the newly set erase position, and DC erase is performed for one round.
Next, as shown in step 105 in FIG. 6, the read head (center thereof) is moved to the track edge on the inner periphery side of the test track (the edge position of the data track 32 indicated by 33 in FIG. 4). Play back the residual signal after erasure. The reproduction signal is input to the read / write amplifier 14 via the MR signal line 16 and amplified to an amplitude of about 100 to 200 mVpp. This signal is input to the signal input terminal of the spectrum analyzer 7 via the lead signal line 13.
Next, as shown in step 106 in FIG. 6, the spectrum analyzer 7 performs frequency analysis of the reproduction signal to obtain a spectrum. Therefore, first, the analysis frequency range of the spectrum analyzer 7 is set to, for example, 0 Hz to 200 MHz, and the analysis frequency resolution is set to 100 Hz. Then, sweep of the spectrum analyzer 7 is executed, and a spectrum image is displayed on the monitor screen of the spectrum analyzer 7. As shown in FIG. 5, this spectrum includes a signal component of a 10 MHz fundamental wave (H1) and odd harmonics (H3, H5, H7,...), And a noise component 50 that extends substantially in the analysis frequency range. It is out.

Next, as shown in step 107 of FIG. 6, the signal strength of the reproduction signal is measured. Therefore, the peak amplitude value of the 10 MHz fundamental wave component (H1) is read from the spectrum image on the monitor screen of the spectrum analyzer 7. This is recorded as a value corresponding to the erase position.
Next, as shown in step 108 of FIG. 6, it is determined whether or not the end condition is satisfied. As the end condition, for example, the reduction rate of the signal strength of the residual signal in step 107 and the distance between the current erase position and the center position of the test track are set as conditions. In the former case, for example, it is determined that the termination condition is satisfied when the signal strength of the residual signal is reduced to less than 50% with respect to the maximum value.
If the end condition is not satisfied, the measurement is continued, and the media noise of the residual signal is calculated as shown in Step 109 of FIG. Therefore, the area of the portion indicated by hatching in the spectrum of the residual signal obtained in step 106 in FIG. 6 is obtained. This is recorded as a value corresponding to the erase position.

Next, as shown in step 110 of FIG. 6, the erase position is moved in the outer peripheral direction (test track direction) by a minute amount to set a new erase position. Next, returning to step 104 in FIG. 6, the write head is moved to the newly set erase position, and erase is performed again for one round.
Similarly, the processing from step 104 to step 110 in FIG. 6 is repeated. As the number of repetitions increases, the erase position gradually approaches the center of the test track. As a result, the test track is gradually erased from the inner peripheral side, the signal strength of the residual signal is reduced, and the measured value of the media noise is also gradually reduced.
Therefore, as shown in FIG. 4, the value of the erase position vs. signal intensity data 40 and the value of the erase position vs. media noise data 41 both show a characteristic that decreases monotonously from a certain head position. As shown in FIG. 4, the head position where the value of the erase position vs. media noise data 41 starts to decrease is smaller than the head position where the value of the erase position vs. signal strength data 40 starts to decrease. It is closer to the inner circumference by 31.

By repeating the process from step 104 to step 110 in FIG. 6 several times, the end condition in step 108 described above is satisfied, and the process is completed to calculate the erase bandwidth from the measurement data after completing the repetition. Move.
First, as shown in step 111 of FIG. 6, the head position (first erase position) P1 at which the signal intensity starts to decrease is obtained from the erase position versus signal intensity data 40. Therefore, first, as shown in FIG. 4, at each data point of the erase position versus signal strength data 40, a straight line L1 that approximates a data point having a signal strength in the range of, for example, 50% to 90% of the maximum value is obtained. Next, at each data point of the erase position versus signal intensity data 40, a straight line L2 that approximates several data points on the inner circumference side is obtained. Further, the intersection of L1 and L2 is calculated, and the head position P1 at the intersection is obtained.

Next, as shown in step 112 of FIG. 6, the head position (second erase position) P2 at which the media noise starts to decrease is obtained from the erase position versus media noise data 41. Therefore, first, as shown in FIG. 4, at each data point of the erase position versus media noise data 41, a straight line L3 that approximates a data point in which the media noise is in the range of 50% to 90% of the maximum value is obtained. Next, at each data point of the erase position versus media noise data 41, a straight line L4 that approximates several data points on the inner circumference side is obtained. Further, the intersection of L3 and L4 is calculated, and the head position P2 at the intersection is obtained.
Finally, as shown in step 113 of FIG. 6, the absolute value of the difference between P1 and P2 is calculated, and this is set as the erase bandwidth.
The series of processes described above are performed almost automatically by the program of the controller 11 shown in FIG. The time required for measurement is about several minutes per time. On the other hand, the conventional MFM method requires 30 to 40 minutes including the adjustment time of the apparatus.

In the present embodiment, an example is described in which measurement is performed while gradually shifting the erase position toward the outer periphery from the inner periphery of the test track toward the center of the test track, but from the outer periphery of the test track to the center of the test track. The measurement may be performed while gradually shifting the erase position in the inner circumferential direction.
In this embodiment, the case of longitudinal recording in which the track is magnetized in the circumferential direction has been described. However, this method can also be applied to perpendicular recording. The measurement method in that case is the same as that for longitudinal recording.

  According to the present invention, the erase band width is measured by reading / writing the magnetic disk medium with a magnetic head. Therefore, the characteristics of the magnetic head or / and the magnetic disk medium are evaluated based on the measurement result to increase the recording density. Can be used for research and development.

It is a block diagram which shows the read / write test apparatus used for the Example which concerns on this invention. It is explanatory drawing which shows the recording principle to the magnetic disc medium by the write head of a magnetic head. It is a schematic diagram which shows a data track and an erase band. It is explanatory drawing which shows the calculation method of the erase bandwidth of the Example which concerns on this invention. It is a spectrum which shows the residual signal of the Example which concerns on this invention. It is a flowchart which shows the measurement procedure of the erase bandwidth of the Example which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic disk medium 2 Magnetic head 3 Spin stand 9 Read / write test apparatus 20 Recording head 31 Erase band 32 Data track 101,102 Test track recording step 103-110 Erase residual signal measurement step 111-113 Erase band width calculation step P1 1st Erase position of P2 Second erase position

Claims (3)

In the erase band width measuring method for measuring the width of an erase band formed at the end of a track when a signal is recorded on a magnetic disk medium by a magnetic head,
A test track recording step of recording a periodic signal of a predetermined frequency on the test track by the magnetic head after DC erasing at least the periphery of the test track of the magnetic disk medium whose width of the erase band is to be measured;
Each erase position is sequentially DC erased by the magnetic head while the erase position adjacent to the test track of the magnetic disk medium is gradually moved to the center of the test track, and each erase position is subjected to DC erase. Erasing the residual signal at the track edge of the test track, measuring the signal strength and media noise of the residual signal, and recording the recorded residual signal;
An erase bandwidth calculation method, comprising: an erase bandwidth calculation step of calculating the width of the erase band based on measurement data of the signal strength of the residual signal and media noise for each erase position. The erase bandwidth calculating step includes:
Calculating from the measurement data of the signal strength of the residual signal for each erase position, a first erase position where the signal strength starts to decrease due to DC erase;
Calculating a second erase position where the media noise starts to decrease due to DC erase from the measurement data of the media noise of the residual signal for each erase position;
The method according to claim 1, further comprising: calculating an absolute value of a difference between the first erase position and the second erase position as an erase band width.   The magnetic head includes a recording head and a reproducing head, the DC erase and recording of a periodic signal of a predetermined frequency are performed using the recording head, and the residual signal is reproduced using the reproducing head. The method for measuring an erase bandwidth according to claim 1 or 2.

Images