JP2682042B2 - Magnetic head - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a composite magnetic head including a junction ferrite of a single crystal ferrite and a polycrystalline ferrite.

SUMMARY OF THE INVENTION The present invention relates to a composite type magnetic head using single crystal ferrite in a sliding contact portion of a magnetic recording medium and using polycrystalline ferrite in a portion forming a rear magnetic circuit, wherein the single crystal ferrite and the polycrystalline ferrite are used. By interposing an intermediate layer on the bonding interface of, the size of the waviness of the bonding interface due to the growth of the single crystal ferrite accompanying the bonding of the single crystal ferrite and the polycrystalline ferrite is regulated to improve the bonding strength at the bonding interface. Moreover, it is intended to reduce the sliding noise level.

[Conventional technology]

In recent years, high density recording and short wavelength recording have been promoted with the advent of so-called digital video tape recorders and the demand for miniaturization and longer time of devices such as video tape recorders (VTRs). Coercive force magnetic recording media have come into use.

Therefore, research has been conducted in the field of magnetic heads to deal with these problems. For example, a VTR head that requires a high recording density has a high saturation magnetic flux density at a high frequency of about 5 MHz and has a single magnetic ferrite having a relatively large magnetic permeability. Magnetic heads have been proposed. However, this single ferrite head has a drawback that the level of sliding noise is high.

Therefore, a magnetic head has been proposed in which the sliding noise level is reduced by reducing the proportion of the single crystal ferrite. This magnetic head has a so-called bonded structure in which the sliding contact portion of the magnetic recording medium is formed of single crystal ferrite having a high saturation magnetic flux density, and the remaining magnetic circuit portion is formed of polycrystalline ferrite having a high magnetic permeability. It is a ferrite type magnetic head. The above-mentioned bonded ferrite magnetic head has a simple structure similar to that of the single ferrite head, but is capable of high-density recording and achieves reduction of sliding noise level.

However, in the above-mentioned bonded ferrite magnetic head, the single crystal ferrite and the polycrystalline ferrite are subjected to hot pressure treatment, that is, in a nitrogen atmosphere at a temperature condition of about 1200 to 1300 ° C. and a temperature of about 4 to 5 kg / cm ^2. Since the single crystal ferrite portion is directly bonded under the pressure of (1), the single crystal ferrite portion grows (solid phase diffusion), and a part of the polycrystalline ferrite becomes single crystal ferrite. The diffusion layer appears as a waviness at the bonding interface, and sometimes the waviness reaches 300 μm. Also, since the size of the diffusion layer is different at each interface,
It has a drawback that the magnetic head has a large variation in the length of the single crystal ferrite portion, which substantially increases the sliding noise level.

For example, when the bonded ferrite magnetic head is a VTR magnetic head, the length of the single crystal ferrite portion (including the length of the diffusion layer) and the sliding noise are closely related to each other.
Sliding noise tends to increase as the length of the single crystal ferrite portion increases.

Therefore, it is ideal that the length of the single crystal ferrite portion should be substantially equal to the depth of the magnetic gap in consideration of the life of the head, and the joint interface should not be exposed on the sliding surface of the magnetic recording medium. For example, in the case of a VTR magnetic head having a head chip width of about 2 mm in the medium running direction, the length of the single crystal ferrite portion is required to be about 70 μm, which shows an extremely small sliding noise level.

However, since the diffusion layer is formed at the bonding interface and the length of the single crystal ferrite is substantially increased by the hot pressure treatment as described above, it is very difficult to control the length of the single crystal ferrite. It is not easy to reduce the sliding noise level.

Therefore, the applicant of the present application prevents solid phase diffusion of the single crystal ferrite by interposing an intermediate film such as an oxide magnetic film at the bonding interface as disclosed in Japanese Patent Application No. 61-158987. A magnetic head designed to do so is proposed.

According to this magnetic head, the solid phase diffusion of the single crystal ferrite can be completely blocked, so that no diffusion layer is formed at the bonding interface and no waviness occurs. Therefore, since the length of the single crystal ferrite portion can be easily controlled, the length of the single crystal ferrite portion can be positioned at the depth of the magnetic gap, whereby the sliding noise level is reduced to the polycrystalline ferrite. It is about the same as a single ferrite head made of only.

However, although the sliding noise level can be reduced with the above magnetic head, the bonding strength at the bonding interface is reduced. That is, the hot pressing treatment may not provide sufficient bonding strength, and peeling may occur between the single crystal ferrite portion and the polycrystalline ferrite portion. Further, it may be peeled off from the bonding interface during the process of forming a head chip.

[Problems to be solved by the invention]

Therefore, the present invention has been proposed in view of such conventional circumstances, and secures the bonding strength at the bonding interface by controlling the size of the waviness of the bonding interface due to the growth of single crystal ferrite, and the sliding An object of the present invention is to provide a bonded ferrite type magnetic head having an extremely low dynamic noise level.

[Means for solving the problem]

The inventors of the present invention have conducted extensive studies for many years to achieve the above-mentioned object, and as a result, do not completely block the solid-phase diffusion of single-crystal ferrite by the hot press treatment, but the magnitude of the diffusion. It was found that by regulating the thickness within a predetermined range, sufficient bonding strength at the bonding interface can be obtained, and at the same time, the reduction of the sliding noise level can be satisfied.

The present invention has been completed based on such findings, and in a composite type magnetic head using a polycrystalline ferrite in a portion forming a rear magnetic circuit using a single crystal ferrite in a magnetic recording medium sliding contact portion, The maximum value of the waviness of the joint interface due to the growth of the single crystal ferrite accompanying the joint between the single crystal ferrite and the polycrystalline ferrite is 10 μm or more and 30 μm or less, with an intermediate layer interposed at the joint interface between the single crystal ferrite and the polycrystalline ferrite. It is characterized by

[Action]

According to the magnetic head of the present invention, the intermediate layer is interposed at the bonding interface between the single crystal ferrite and the polycrystalline ferrite, and the growth of the single crystal ferrite accompanying the bonding between the single crystal ferrite and the polycrystalline ferrite is caused by this intermediate layer. Since the size of the waviness of the joint interface due to is regulated to a range that does not hinder the sliding noise level in practical use, sufficient joint strength can be obtained and the sliding noise level can be reduced at the joint interface.

Therefore, the problem of peeling from the bonding interface is solved, so that the yield is improved and high reliability is obtained. Further, since the length of the single crystal ferrite can be controlled to an appropriate value, the length of the single crystal ferrite can be matched with the depth of the magnetic gap, and the sliding noise level can be further reduced.

〔Example〕

Hereinafter, a specific embodiment of the present invention will be described with reference to the drawings.

As shown in FIGS. 1 and 2, the bonded ferrite type magnetic head of the present embodiment includes a single crystal ferrite portion (1) forming a magnetic gap g on the sliding contact surface side of the magnetic recording medium,
It is configured by joining and integrating a polycrystalline ferrite portion (2), which occupies most of the magnetic circuit on the back gap side of the magnetic head, via an intermediate layer (3) made of an oxide magnetic thin film. A track width regulating groove for regulating the track width to a predetermined value may be cut out in the vicinity of the magnetic gap g.

In the bonded ferrite type magnetic head, in order to cope with a magnetic recording medium having a high coercive force, the magnetic gap is made of single crystal ferrite having a high saturation magnetic flux density. On the other hand, most of the magnetic circuit except the head chip portion near the front gap is made of polycrystalline ferrite having high magnetic permeability for the purpose of increasing the average magnetic permeability of the entire magnetic head. As a result, at the time of recording, the entire magnetic head exhibits the same characteristics as those made of a high saturation magnetic flux density material, and it is possible to perform sufficient recording on a high coercive force magnetic recording medium. Since the average magnetic permeability of is high, it exhibits excellent electromagnetic conversion characteristics.

In the present invention, the single crystal ferrite part (1)
And a polycrystalline ferrite part, an intermediate layer (3) made of an oxide magnetic thin film is interposed between the single crystal ferrite part (1) and the polycrystalline ferrite part (2). A major feature is that the maximum value of the waviness of the bonded interface due to the growth of the portion (1) (hereinafter referred to as solid phase diffusion) is set to 10 μm or more and 30 μm or less.

According to this, the solid phase diffusion of the single crystal ferrite part (1) is not completely blocked at the joint interface, but the maximum value of the undulation magnitude of the solid phase diffusion is not a practical problem. The magnetic head is regulated to have a level range and a size capable of obtaining reliable bonding strength at the bonding interface, so that the bonding strength at the bonding interface can be secured, and at the same time, the reduction of the level of sliding noise can be satisfied.

Therefore, peeling from the bonding interface due to insufficient bonding strength in the hot pressing process and peeling due to stress or the like generated in the step of forming a head chip will not occur.
Therefore, the yield is improved and high reliability is obtained.

The maximum value of the undulation is 10 μm or more and 30 μ
Since it is m or less, it is extremely small in this range as compared with the waviness of the bonded ferrite head without the intermediate layer interposed therebetween, and is a sliding noise level range that does not pose a practical problem.

Examples of the intermediate layer (3) include Mn-Zn ferrite, Mn ferrite, Ni-Zn ferrite, Ni ferrite, Fe-Zn ferrite, and Fe ferrite. In this example, Mn-Zn ferrite was used.

These intermediate layers (3) can be easily formed by a vacuum thin film forming technique such as a sputtering method or a vacuum evaporation method. In addition, in the present embodiment, it is formed by the sputtering method.

In order to manufacture the magnetic head of the present embodiment, first, a single crystal ferrite block and a polycrystalline ferrite block are prepared, and the bonding surface of these is mirror-finished, and then the surface of the single-crystal ferrite block mirror-finished. Then, a Mn-Zn ferrite thin film is sputtered to a film thickness of about 0.1 to 0.75 μm, and then bonded and integrated by hot pressure treatment to form a bonded ferrite block. Then, the magnetic head of this embodiment is completed by subjecting the bonded ferrite block to ordinary winding processes such as winding groove processing and track restriction groove processing.

Here, the present invention will be described with reference to experimental data of a magnetic head actually manufactured by the present inventors.

First, as shown in FIG. 3, Bridgma (Bridgma)
n) Single crystal ferrite block formed by method (4)
And a polycrystalline ferrite block (5) formed by an ordinary powder metallurgy method are prepared, and these joint surfaces are mirror-polished so that the maximum height Rmax of the surface roughness of the joint surfaces becomes 0.1 to 0.3 μm. I chose A ferrite having the following composition was used for the single crystal ferrite block (4) and the polycrystalline ferrite block (5).

Single crystal ferrite composition MnO 30.0mol% ZnO 20.0mol% Fe ₂ O ₃ 50.0mol% Polycrystalline ferrite composition MnO 30.0mol% ZnO 20.0mol% Fe ₂ O ₃ 50.0mol% Next, the single crystal ferrite block (4) A Mn-Zn ferrite thin film (6) was deposited on the joint surface by sputtering. In this example, high frequency magnetron sputtering was used to perform sputtering under the following conditions.

Sputtering conditions Pressure ・ ・ ・ 1Pa Discharge gas ・ ・ ・ Ar output ・ ・ ・ 4W / cm ² Target composition ・ ・ ・ MnO 25.0mol%, ZnO 25.0mol
%, Fe ₂ O ₃ 50.0 mol% Next, the single crystal ferrite block (4) and the polycrystalline ferrite block (5) were joined and integrated by hot pressing. The processing conditions for hot pressurization are the bonding temperature of 1300
℃, pressurization pressure 5.0kg / cm ² , treatment time 2 hours, nitrogen atmosphere.

In this example, a total of 9 types of bonded ferrite blocks were produced by varying the film thickness of the Mn-Zn ferrite thin film (6) within the range of 0 to 2.0 μm.

Next, these bonded ferrite blocks bonded and integrated were cut and polished (chrome lap), and then the bonding interface was observed with a microscope to examine the bonding strength. The bond strength is
10 samples with peeling at the joint interface,
It was divided into three stages: one with spot peeling (when there are spot-like holes on the joint surface) and one without peeling, and the number of each was evaluated. Further, after etching the bonded ferrite block with hydrochloric acid, the magnitude of solid phase diffusion of the single crystal ferrite portion was measured. In this example, both the maximum value of the waviness of the solid phase diffusion, that is, the maximum solid phase diffusion length, and the average value of the waviness size, that is, the average solid phase diffusion length were measured. Table 1 shows the results.

Then, a part of the bonded ferrite block was cut out and subjected to winding groove processing, track width regulation groove processing and the like to manufacture the magnetic head shown in FIGS. 1 and 2. The length of the single crystal ferrite part of this magnetic head is 70μ.
m. Then, the sliding noise level of these magnetic heads was measured.

FIG. 4 is a plot of the maximum solid phase diffusion length dependence of the sliding noise level and the peeling / spot peeling failure rate based on these experimental results.

As is clear from FIG. 4, the bonding strength increases as the maximum solid phase diffusion length of the single crystal ferrite part increases,
Conversely, sliding noise tends to increase. That is, sliding noise increases when trying to secure the joining strength, and conversely, when trying to lower the sliding noise level, the joining strength decreases this time. It is in.

Therefore, in order to satisfy both the bonding strength and the sliding noise, it is necessary to set the maximum solid phase diffusion length of the single crystal ferrite portion within an appropriate range. That is, it is necessary to find a range in which the bonding strength can be sufficiently secured and the sliding noise level can be satisfied at the same time. In order that the sliding noise level does not pose a practical problem, it is necessary that the amount of increase in the sliding noise level before the hot pressing treatment and after the hot pressing treatment be 2 dB or less. As seen from Fig. 4, the maximum solid phase diffusion length of the single crystal ferrite part where the amount of sliding noise increase is 2 dB or less and the bonding strength is sufficiently secured is 10 μm to 30 μm.
The range is as follows. Therefore, by setting the maximum solid phase diffusion length of the single crystal ferrite portion within the above range, both the bonding strength and the sliding noise can be satisfied at the same time, and a magnetic head with excellent reliability can be realized.

Then, next, in order to investigate the relationship between the maximum solid phase diffusion length and the film thickness of the intermediate layer, the dependence of the maximum solid phase diffusion length and the peeling / spot peeling defect rate on the film thickness of the intermediate layer was plotted. The results are shown in FIG.

As a result, the thickness of the intermediate layer (6) for which the maximum solid phase diffusion length is within the above range is, as is clear from FIG.
In the case of Zn ferrite, it was 0.1 to 0.75 μm. The range of the film thickness depends on the material of the intermediate layer (6).

Therefore, the membrane pressure of the intermediate layer (6) should be 0.1-0.75μ.
If it is set to m and is interposed at the joint interface between the single crystal ferrite and the polycrystalline ferrite, the maximum solid phase diffusion length of the single crystal ferrite due to the joint between the single crystal ferrite and the polycrystalline ferrite is 10 μm or more and 30 μm or less. Regulated within the range of. Therefore, the bonding strength at the bonding interface is close to the bonding strength of the bonded ferrite magnetic head without the intermediate layer (6), and a very low sliding noise level is achieved.

Further, since the magnitude of the solid phase diffusion of the single crystal ferrite can be regulated, it becomes possible to match the length of the single crystal ferrite portion with the depth of the magnetic gap. Therefore, the magnetic head capable of further reducing the sliding noise level is achieved.

〔The invention's effect〕

As is clear from the above description, in the present invention, an intermediate layer is interposed at the bonding interface between the single crystal ferrite and the polycrystalline ferrite, and the single crystal accompanying the bonding of the single crystal ferrite and the polycrystalline ferrite is formed by this intermediate layer. Since the maximum value of the waviness of the bonding interface due to the growth of ferrite is regulated within a predetermined range, a highly reliable bonding strength close to the bonding strength of a bonded ferrite magnetic head without an intermediate layer can be obtained. The sliding noise level is extremely low.

Therefore, according to the magnetic head of the present invention, the occurrence of peeling from the bonding interface due to insufficient bonding strength in the hot pressing process and peeling due to stress or the like generated in the intermediate step of head chip processing is eliminated, and the yield in the manufacturing process is reduced. Is improved and a highly reliable magnetic head is realized.

Further, since the magnitude of the solid phase diffusion of the single crystal ferrite can be regulated, the length of the single crystal ferrite can be matched with the depth of the magnetic gap, and the sliding noise level can be further reduced.

[Brief description of the drawings]

FIG. 1 is an external perspective view showing an example of a magnetic head to which the present invention is applied, and FIG. 2 is a sectional view taken along the line AA in FIG. FIG. 3 is a perspective view showing a bonded ferrite block which has been subjected to hot pressure treatment and bonded and integrated. FIG. 4 is a characteristic diagram showing the maximum solid-phase diffusion length dependency of sliding noise and peeling / point peeling defect rate. FIG. 5 is a characteristic diagram showing the dependence of the maximum solid phase diffusion length and the peeling / spot peeling defect rate on the thickness of the intermediate layer. 1 …… Single crystal ferrite part 2 …… Polycrystalline ferrite part 3 …… Intermediate layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiko Isoyama 6-5-6 Kitashinagawa, Shinagawa-ku, Tokyo Sony Magne Products Co., Ltd. (56) Reference JP-A 63-14311 (JP, A) ) JP-A-63-184903 (JP, A)

Claims (1)

(57) [Claims] 1. A composite magnetic head using a single crystal ferrite in a sliding contact portion of a magnetic recording medium and a polycrystalline ferrite in a portion constituting a rear magnetic circuit, wherein a junction interface between the single crystal ferrite and the polycrystalline ferrite is provided. The maximum value of the waviness of the joint interface due to the growth of the single crystal ferrite due to the joining of the single crystal ferrite and the polycrystalline ferrite with the intermediate layer interposed is 10 μm to 30 μ.
A magnetic head having a thickness of m or less.