JPH0985738A - Cutting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the removing work of an adherent wax remaining in respective grooves which are provided on the affixing surface of a jig, and in addition, surely prevent chippings on a block from generating when each chip is cut out by applying a cutting process on each block being cut out from a wafer. SOLUTION: A solid adherent wax is dissolved with a volatile organic solvent to make a liquid adhesive, and after applying the liquid adhesive on an affixing surface 34a of a jig 34, a low bar 42 is mounted on the applicable affixing surface 34a. At the same time, the applied liquid adhesive is heated, and the low bar 42 is bonded and fixed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cutting method in which each block cut out from a wafer is cut into a predetermined width and each chip is cut out. The present invention relates to a cutting method for cutting each slider individually from a non-magnetic block formed into a film.

[0002]

2. Description of the Related Art In recent years, as hard disk drives have become smaller and larger in capacity, in particular, for applications that are considered to be applied to portable computers typified by notebook personal computers, for example, about 2.5 inches. There is a growing demand for smaller hard disk drives.

[0003] In such a small hard disk, the medium speed becomes slow depending on the disk diameter. Therefore, in the conventional inductive magnetic head in which the reproduction output depends on the medium speed, the reproduction output is reduced and the increase in capacity is hindered. It has become.

On the other hand, a magnetoresistive head (hereinafter referred to as a magnetoresistive head) which detects a change in resistance of a magnetic layer (hereinafter, simply referred to as an MR element) having a magnetoresistive effect whose resistivity changes according to a magnetic field as a reproduction output voltage. , Which is simply referred to as an MR head.) Has a feature that its reproduction output does not depend on the medium speed and that a high reproduction output can be obtained even at a low medium speed. Therefore, it is noted as a magnetic head that realizes a large capacity in a small hard disk. Has been done.

[0005] This MR head is a reproducing magnetic head utilizing a so-called magnetoresistance effect phenomenon, in which the electric resistance changes depending on the angle between the direction of the magnetization observed in the transition metal and the direction of the current flowing inside the transition metal. That is, when the MR element receives the leakage magnetic flux from the magnetic recording medium, the direction of the magnetization of the MR element is reversed by the magnetic flux, and the MR element
It has an angle corresponding to the magnetic amount with respect to the direction of the current flowing inside the element. Therefore, the electric resistance value of the MR element changes, and a voltage change corresponding to the change amount appears on the electrodes at both ends of the MR element through which the current flows. Therefore, a magnetic recording signal can be read using this voltage change as a voltage signal.

The MR head is formed by forming the MR element, the electrode film, the insulating layer, etc. on a substrate by a thin film technique and etching them into a predetermined shape by a photolithography technique. In order to prevent unwanted magnetic flux from entering the MR element by defining the above, a shield structure in which a lower magnetic layer and an upper magnetic layer, which serve as shield materials, are arranged vertically is adopted.

Specifically, for example, in a so-called vertical MR head device in which a sense current flows in a direction orthogonal to the track width direction, a lower magnetic layer which is a soft magnetic film on a non-magnetic substrate, and Al ₂ O. Insulating layers made of ₃ or SiO ₂ etc. are sequentially laminated, and the MR element is formed on the insulating layer.
It is arranged such that its longitudinal direction is perpendicular to the surface facing the magnetic recording medium (the magnetic recording medium running surface), and one end face of the magnetic recording medium is exposed to the magnetic recording medium running surface a. Further, on the both ends of the MR element, the MR
A front electrode and a rear electrode for providing a sense current to the element are provided, and an insulating layer made of Al ₂ O ₃ or SiO ₂ is formed on the MR element. A bias conductor is arranged on the insulating layer so as to face the MR element, an insulating layer is further formed on the bias conductor, and an upper magnetic layer, which is a soft magnetic film, is stacked on the insulating layer to form an MR head portion. It is configured. Here, in the MR element, a region between the front end electrode and the rear end electrode serves as an effective magnetic sensing part.

Then, a predetermined groove is formed in the slider surface, which is a surface substantially orthogonal to the MR head forming surface of the non-magnetic substrate, and a slider rail is formed to constitute the MR head device.

Along with this vertical type MR head part, a so-called horizontal type MR head part in which a sense current flows in a direction parallel to the track width direction is also used. In this horizontal MR head, the MR element is arranged such that its longitudinal direction is parallel to the magnetic recording medium running surface with the magnetic recording medium.

Since the MR head part has a structure in which the MR element is sandwiched between the upper magnetic layer and the lower magnetic layer, the resolution is improved, and the reproduction output S is higher than that without the upper and lower magnetic layers. / N and recording density can be improved.

Now, a method of manufacturing the MR head device will be described.

First, a plurality of the above-mentioned MRs are formed at predetermined intervals on a wafer made of a non-magnetic material such as Al ₂ O ₃ —TiC.
The head portion is formed into a film by a thin film forming technique such as sputtering.

Then, after trimming the wafer to cut off unnecessary portions of the outer peripheral portion of the wafer,
The thin film (protective film) portion formed on the cutting line of the wafer is cut off.

Then, the above-mentioned wafer is cut into individual MRs.
A plurality of non-magnetic blocks (row bars) having head portions formed in one row are manufactured. This row bar has a rectangular parallelepiped shape, and one main surface thereof is the MR head portion forming surface.
One surface that is substantially orthogonal to the MR head portion forming surface becomes the slider surface on which the slider rail is formed.

Next, the solid adhesive wax is heated to a high temperature to be softened, and the wax is applied to the attachment surface of a predetermined jig. Then, the row bar is placed on the sticking surface and fixed by adhesion with the adhesive wax.

Subsequently, a diamond cup wheel is used to roughly grind the slider surface to a depth of several .mu.m, and then the slider surface is grooved to form a slider rail.

Then, the row bar is ground by using a rotary grindstone so as to correspond to the grooves formed on the attachment surface of the jig, and each head chip is cut, and the depth is set on the slider surface. After polishing, taper processing and air inflow groove processing are performed to a specified head depth value.

Thereafter, the head chip is removed from the jig to complete the MR head device.

[0019]

[Problems to be Solved by the Invention]
When the bar is ground and cut into each head chip, specifically, as shown in FIG.
1 on the attachment surface 102a of the jig 102
The adhesive wax applied to a is fixed by adhesion. At this time, since the adhesive wax has a high viscosity even when it is softened by high temperature, the adhesive wax is cut on the attaching surface 102a of the jig 102 as shown in the drawing.
It will remain in b.

In this state, as shown in FIG. 19, each groove 10
The low bar 10 by the rotating grindstone 103 corresponding to 2b
Since 1 is ground, when the rotary grindstone 103 that cuts the row bar 101 passes through the groove 102b, the rotary grindstone 103 passes through the adhesive wax solidified in the groove 102b. Therefore, the rotary grindstone 103
In addition to clogging, the grinding accuracy is deteriorated, and chipping (chip chipping) t occurs especially on the surface of the row bar 101 where the MR head is formed.

To prevent the chipping t from occurring,
After applying the adhesive wax to the application surface 102a, each groove 1
It is necessary to remove the residual adhesive wax in 02b, thus causing a reduction in processing efficiency.

Therefore, the present invention has been made in view of the above-mentioned problems, and an object thereof is to attach a jig when cutting each block cut out from a wafer to cut out each chip. An object of the present invention is to provide a cutting method that does not require the work of removing the adhesive wax remaining in each groove formed in the surface and can reliably suppress the occurrence of chipping in the block. .

[0023]

The object of the present invention is a cutting method in which each block cut out from a wafer is cut to a predetermined width to cut out each chip.

According to the present invention, a solid adhesive wax is dissolved in a volatile organic solvent to form a liquid adhesive, the liquid adhesive is applied to the sticking surface of the jig, and then the block is mounted on the sticking surface. Placing and placing a volatile organic solvent contained in the applied liquid adhesive to volatilize and adhere and fix,
Corresponding to each groove cut on the pasting surface of the jig,
A step of grinding the above block using a rotary grindstone and cutting each chip.

In this case, the block is mainly a non-magnetic block formed by forming a plurality of thin film magnetic head portions by a vacuum thin film forming technique, and adheres to the attaching surface of the jig as described above. After a predetermined groove is formed on a slider surface of the fixed non-magnetic block that is substantially orthogonal to the thin-film magnetic head portion forming surface, the non-magnetic block is cut to cut out each head chip.

Furthermore, the present invention is preferably applied to a magnetoresistive effect type magnetic head part having a magnetoresistive effect element having a magnetoresistive effect in which the resistivity changes according to a signal magnetic field from a magnetic recording medium, as the thin film magnetic head part. Is.

In the present invention, the concentration of the adhesive wax in the liquid adhesive is 10% by weight or more and 70% by weight or more.
The wax concentration is preferably the following, and more preferably, the wax concentration is set to 30% by weight or more and 50% by weight or less. Here, when the wax concentration is less than 10% by weight, the adhesive strength is deteriorated, and when the wax concentration is more than 70% by weight, the adhesion in each groove cut on the sticking surface of the jig after heating. This is inconvenient because the filling rate of the wax is high.

As described above, in the present invention, the liquid adhesive prepared by dissolving the solid adhesive wax in the volatile organic solvent is applied to the attachment surface of the jig, and the block is placed and applied. The volatile organic solvent contained in the liquid adhesive is volatilized by heating or the like to bond and fix. In this case, the liquid adhesive is in a state of being diluted with the volatile organic solvent when the block is placed on the attachment surface of the jig, but by heating the liquid adhesive, the volatile organic solvent which is the solvent It completely volatilizes and has a wax concentration equivalent to that of a normal solid adhesive wax. Therefore, since the volatile organic solvent is completely volatilized by heating the liquid adhesive accumulated in each groove cut on the attachment surface of the jig, the filling rate of the adhesive wax remaining in the groove is Small, even when the rotating grindstone cuts the block and enters the groove during cutting of the block, since the adhesive wax hardly remains, clogging of the rotating grindstone is prevented, and The chipping that tends to occur in blocks is suppressed.

In the liquid adhesive, the mixing ratio of the volatile organic solvent which is a solvent and the adhesive wax which is a solute can be freely changed. Therefore, the wax concentration should be adjusted according to various conditions. Is possible.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments in which the cutting method according to the present invention is applied to a magnetoresistive effect magnetic head device (MR head device) will be described in detail below with reference to the drawings.

In this MR head device, as shown in FIG. 1, a magnetoresistive effect head portion A which is a constituent element of the MR head device.
The (MR head portion A) is formed so that its longitudinal direction is orthogonal to the magnetic recording medium running surface a and exhibits a magnetoresistive effect M.
The R element 1 is structured so as to be sandwiched between the lower magnetic layer 2 and the upper magnetic layer 3, and is configured as a so-called vertical MR magnetic head portion.

Specifically, Ni--Fe is formed on one main surface of the nonmagnetic substrate 11 made of a nonmagnetic material such as Al ₂ O ₃ --TiC.
A lower magnetic layer 2 which is a shield magnetic film made of, for example, is provided, and an insulating layer 12 made of silicon dioxide (SiO ₂ ) or the like is laminated on the lower magnetic pole 2.

Further, the MR element 1 is formed on the insulating layer 12, and the insulating layer 13 made of SiO ₂ or the like is formed on the MR element 1. That is, in the MR head, the MR element 1 is arranged such that its longitudinal direction is perpendicular to the surface facing the magnetic recording medium, that is, the running surface a of the magnetic recording medium, and the front end surface of the MR element 1 runs. It is exposed on the surface a.

The MR element 1 is provided on the insulating layer 13.
Bias conductor 1 for applying a predetermined bias magnetic field to the
5 is formed, and the insulating layer 16 is formed on the bias conductor 15. Here, the bias conductor 15 is formed so as to be embedded in the insulating layer 16.

Here, one end of the MR element 1 on the side of the magnetic recording medium running surface a and the other end separated by a predetermined distance from the one end are electrodes made of a conductive film (front end electrode 14a and rear end electrode 14b). Are formed. These front end electrodes 14
The a and the rear end electrode 14b are formed for the purpose of flowing a sense current along the longitudinal direction of the MR element 1 (that is, in the direction orthogonal to the magnetic recording medium running surface a). That is, the MR element 1 is sandwiched by the front-end electrode 14a and the rear-end electrode 14b.
The area between the front and rear electrodes 14a and 14b serves as an effective magnetic sensing section exhibiting a magnetoresistive effect. At this time, the distance from the running surface a of the magnetic recording medium to the effective magnetic sensing portion via the front end electrode 14a is the depth length.

The MR head portion A is constructed by laminating the upper magnetic layer 3 of a magnetic film such as Ni--Fe so as to sandwich the MR element 1 on the front end electrode 14a.

Here, as shown in FIG. 2, the nonmagnetic substrate 11 is, for example, a surface which is substantially orthogonal to the MR head portion forming surface 22 on which the pair of MR head portions A and the wiring connecting portions 21 are formed. It has a certain slider surface 23. The MR head device is constructed by forming a groove portion 24, which is an air inflow groove, in a substantially central portion of the slider surface 23 in parallel with the longitudinal direction of the non-magnetic substrate 11 to form a pair of slider rails 25 and 26. ing.

The method of manufacturing the MR head device will be described below.

First, a plurality of the above-mentioned MRs are formed at predetermined intervals on a wafer made of a non-magnetic material such as Al ₂ O ₃ —TiC.
The head portion A is formed into a film by a thin film forming technique such as sputtering.

That is, first, a lower magnetic layer made of a soft magnetic material, an insulating layer 12 made of SiO ₂ or the like for forming a magnetic gap, and Ni--Z are formed on one main surface of the wafer.
An MR film made of n or the like is sequentially formed. Then, the MR film is subjected to predetermined patterning by photolithography and etched to form a plurality of MR elements 1.

Next, after forming the insulating layer 13 on the MR element 1, a connection hole leading to the rear end of the MR element 1 is formed in the insulating layer 13, and the MR element 1 is formed on the rear end. A back electrode 14b is formed to provide a sense current.

Then, the MR is inserted through the insulating layer 13.
Bias conductor 1 for applying a bias magnetic field to the element 1
5 is formed, and the insulating layer 16 is laminated on the rear end electrode 14b and the bias conductor 15.

After forming a connection hole in the insulating layer 13 to the front end of the MR element 1, the MR is formed on the front end.
The front end electrode 14a for providing a sense current to the element 1 is formed, and the upper magnetic layer 3 is formed on the front end electrode 14a, whereby the MR head portion A is completed.

Then, as shown in FIG. 3, the rotary grinding machine 3 is used.
Wafer trimming using 1 to wafer 4
After cutting off the unnecessary portion 41a of the outer peripheral portion of 1, the thin film (protective film) formed on the cutting line of the wafer 41 in the low scribing step by using the rotary grinding machine 32 as shown in FIG. ) Cut off the part.

Then, as shown in FIG. 5, the rotary grinding machine 3 is used.
3, the wafer 41 is cut, and a plurality of non-magnetic blocks (row bar 4) in which each MR head part A is formed in one row
2) is prepared. The row bar 42 has a rectangular parallelepiped shape, and one main surface thereof is the MR head portion formation surface 22. One surface that is substantially orthogonal to the MR head portion forming surface 22 is the slider surface on which the slider rails 25 and 26 are formed.

Next, as shown in FIG. 6, a solid adhesive wax is dissolved in a volatile organic solvent to form a liquid adhesive,
After the liquid adhesive is applied to the sticking surface 34a of the jig 34, the row bar 42 is placed on the sticking surface 34a, and the applied liquid adhesive is heated and bonded and fixed.

The concentration of the adhesive wax in the liquid adhesive is preferably 10% by weight or more and 70% by weight or less, more preferably 30% by weight or more and 50% by weight or less. Set to. Here, when the wax concentration is less than 10% by weight, the adhesive strength is deteriorated, and when the wax concentration is more than 70% by weight, the inside of each groove 34b cut on the attachment surface 34a of the jig 34 after heating. However, the filling rate of the adhesive wax is high, which is inconvenient.

Then, as shown in FIG. 7, the row bar 4
Two jigs 34 to which the adhesive 2 is fixed are collectively fixed, and after the slider surface 23 is roughly ground to a depth of several μm using a diamond cup wheel 35, as shown in FIG. 23 is grooved and the slider rails 25 and 26 are cut.

Then, as shown in FIGS. 9 and 10, the row bar 42 is ground by using a rotary grindstone 36 in correspondence with the grooves 34b formed in the attachment surface 34a of the jig 34. And each head chip 51 is cut.

At this time, the liquid adhesive is in a state of being diluted with the volatile organic solvent when the row bar 42 is placed on the attaching surface 34a of the jig 34, but the solvent is heated by heating the liquid adhesive. The volatile organic solvent is completely vaporized, and the wax concentration becomes equivalent to that of a normal solid adhesive wax. Therefore, as shown in FIG.
The liquid adhesive accumulated in each groove 34b formed in the attachment surface 34a of No. 4 completely volatilizes the volatile organic solvent by heating, so that the filling rate of the adhesive wax remaining in the groove 34b is small. , The row bar 42, as shown in FIG.
Even if the rotary grindstone 36 cuts the row bar 42 and enters into the groove 34b during the cutting process, the clogging of the rotary grindstone 36 is prevented because almost no adhesive wax remains. Therefore, chipping that tends to occur in the row bar 42 is suppressed.

Then, as shown in FIG.
The row bar 42 is fixed so that the slider surface 23 thereof comes into contact with the casting surface plate 37, and the polishing machine 37 is swung and the casting surface plate 37 is rotated to move the slider surface 23 onto the slider surface 23. Depth polishing is performed to obtain a specified head depth value.

Then, as shown in FIG. 14, the slider surface 23 is tapered at a predetermined angle (here, 50 °) on the casting surface plate 38, and as shown in FIG.
After performing the air inflow groove processing using No. 9, the head chip 51 is removed from the jig 34 as shown in FIG. 16, and the MR head device is completed through a predetermined post process.

As described above, according to the cutting method of this embodiment, when the row bars 42 cut out from the wafer 41 are cut and the head chips 51 are cut out, the jig 34 is attached. It is not necessary to remove the adhesive wax remaining in the grooves 34b formed in the surface 34a, and it is possible to reliably prevent the row bar 42 from chipping.

Further, since it is possible to reduce the number of times of dressing (dressing) the rotary grindstone 36, it is possible to suppress the deterioration of the shape of the rotary grindstone 36 due to the dressing and improve the life of the rotary grindstone 36. It will be possible.

Further, the above liquid adhesive has excellent fluidity, and can be applied to an extremely narrow place without causing bubbles, and it is possible to prevent uneven application which tends to occur during application. .

Here, one experimental example will be described.
In this experiment, when the concentration of the adhesive wax (wax concentration) in the liquid adhesive shown in the above-mentioned embodiment is changed, the adhesive wax remains in each groove 34b cut on the attachment surface 34a of the jig 34. Both the filling rate of the adhesive wax and the adhesive strength of the liquid adhesive at this time were examined.

Here, in order to quantitatively measure the filling rate and the adhesive strength, as a sample of the jig 34, as shown in FIG. 17, the groove 52 corresponding to the groove 34b and the attaching surface 34a.
The jig 54 formed with a groove 53 shallower than the groove 52 for checking the state of the portion to which the row bar 42 of FIG.

First, the results of examining the above-mentioned filling rate are shown in Table 1 below. Here, the filling rates of the groove 52 and the groove 53 were measured. The numbers of the grooves 52 and the grooves 53 are 14 and 13, respectively, and of these, the filling rate in the groove in which the adhesive wax remains is shown.

[0059]

[Table 1]

From Table 1, the wax concentration is 70% by weight.
More than half of the grooves 52 remain with the adhesive wax, and the rotating grindstone 36 comes into contact with the solidified adhesive wax in the grooves 34 during the cutting process of the row bar 42 to easily cause chipping. In consideration of safety, it is considered preferable to set the content to 50% by weight or less. Further, in consideration of the state of the groove 53, when the wax concentration is less than 30% by weight, the number of the adhesive wax remaining in the groove 53 becomes 0. Therefore, the wax concentration is preferably 30% by weight or more. .

Next, the results of examining the above-mentioned adhesive strength are shown in Table 2 below. Here, the adhesive strength (Kg) was measured about five samples, and the average value M of these was calculated.

[0062]

[Table 2]

From this Table 2, the wax concentration is 10% by weight.
When it is below the range, the adhesive strength is reduced to the half value at 30% by weight. Therefore, in order to obtain a relatively stable adhesive strength exceeding 2 kg, it is necessary to set the wax concentration to a value of 10% by weight.

From the above results, the wax concentration in the liquid adhesive is preferably in the range of 10 to 70% by weight, and more preferably in the range of 30 to 50% by weight. preferable.

[0065]

According to the cutting method of the present invention, when each block cut out from a wafer is cut and each chip is cut out, it remains in each groove cut on the attachment surface of the jig. The work of removing the adhesive wax becomes unnecessary, and furthermore, the occurrence of chipping in the block can be surely suppressed.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view schematically showing an MR head part which is a component of an MR head device manufactured in this embodiment.

FIG. 2 is a perspective view schematically showing an MR head device manufactured in this embodiment.

FIG. 3 is a perspective view schematically showing a wafer trimming process on a wafer.

FIG. 4 is a perspective view schematically showing a state of a low scribing process.

FIG. 5 is a perspective view schematically showing how a row bar is cut from a wafer.

FIG. 6 is a perspective view schematically showing how a row bar is bonded and fixed to a jig using a liquid adhesive.

FIG. 7 is a perspective view schematically showing a front grinding step.

FIG. 8 is a perspective view schematically showing a slider rail processing step.

FIG. 9 is a perspective view schematically showing a state of a head chip cutting step.

FIG. 10 is an enlarged schematic perspective view of each separated non-magnetic substrate.

FIG. 11 is a cross-sectional view schematically showing a state in a groove cut on the attachment surface of the jig.

FIG. 12 is a cross-sectional view schematically showing a state where a rotary grindstone obtained by cutting a row bar has entered a groove formed in the attachment surface of the jig.

FIG. 13 is a side view schematically showing a state of a depth polishing process.

FIG. 14 is a side view schematically showing a state of a taper processing step.

FIG. 15 is a perspective view schematically showing a state of an air inflow groove processing step.

FIG. 16 is a perspective view schematically showing a state where the head chip is removed from the jig.

FIG. 17 is a cross-sectional view schematically showing a jig in which two types of grooves are cut.

FIG. 18 is a cross-sectional view schematically showing a state in a groove cut on a bonding surface of a jig when performing a conventional cutting method.

FIG. 19 is a cross-sectional view schematically showing a state in which a rotary grindstone that has cut a row bar enters a groove formed in the attachment surface of the jig and chipping occurs in the row bar. .

[Explanation of symbols]

 A MR head part 1 MR element 2 Lower magnetic layer 3 Upper magnetic layer 11 Nonmagnetic substrate 12, 13, 16 Insulating layer 15 Bias conductor 14a Front end electrode 14b Rear end electrode 21 Wiring connection part 22 MR head part forming surface 23 Slider surface 24 Grooves 25, 26 Slider rail 34 Jig 34a Attachment surface 34b Groove 36 Rotating whetstone 41 Wafer 42 Low bar 51 Head chip

Claims (5)

[Claims] 1. When each block cut out from a wafer is cut to a predetermined width and each chip is cut out, a solid adhesive wax is dissolved in a volatile organic solvent to form a liquid adhesive, and this liquid adhesion is performed. Applying the agent to the sticking surface of the jig, placing the block on the sticking surface, and volatilizing the volatile organic solvent contained in the applied liquid adhesive to bond and fix the adhesive; Corresponding to each groove cut on the sticking surface of
And a step of cutting the above blocks by using a rotating grindstone and cutting each block into chips. 2. The cutting method according to claim 1, wherein the concentration of the adhesive wax in the liquid adhesive is 10% by weight or more and 70% by weight or less. 3. The cutting method according to claim 2, wherein the concentration of the adhesive wax in the liquid adhesive is 30% by weight or more and 50% by weight or less. 4. Each block is a non-magnetic block formed by forming a plurality of thin-film magnetic head parts by a vacuum thin-film forming technique, and the thin-film magnetic head part of the non-magnetic block adhered and fixed to a sticking surface of a jig. 2. The cutting method according to claim 1, wherein each head chip is cut by cutting the non-magnetic block after performing a predetermined groove processing on the slider surface substantially orthogonal to the formation surface. 5. The thin-film magnetic head portion is a magnetoresistive effect magnetic head portion having a magnetoresistive effect element that exhibits a magnetoresistive effect in which a resistivity changes according to a signal magnetic field from a magnetic recording medium. Item 4. The cutting method according to item 4.