JPS58128019A - Video head for tape with high corecive force - Google Patents

Abstract

PURPOSE:To obtain a video head having superior wear resistance and enhanced performance by improving the compositional ratio of Fe2O3 in a combination head and the gap length of the head. CONSTITUTION:A combination type video head is formed by interposing a nonmagnetic material 5 between a reproducing head 1 and a recording head 2 and by uniting them in a body. At this time, the gap length 4 of the head 2 is made 1.5-3 times the gap length 3 of the head 1. Single crystals of MnZn ferrite are used as the materials of the cores of the heads 1, 2. The percentage of Fe2O3 in the core of the recording head is adjusted to 65-70mol% so as to regulate the saturation magnetic flux density Bs of the single crystal of MnZn ferrite for the head to 6,000-6,500G. The percentage of Fe2O3 in the core of the reproducing head is adjusted to 45-55mol% so as to regulate the Bs of the single crystal of MnZn ferrite for the head to 4,700-5,300G.

Description

[Detailed description of the invention] The present invention relates to a combination type video head.

Recently, as VTRs have become smaller and lighter, tape width has been reduced to 1/4th.
A VTR has been proposed in which the head/tape relative speed is 3 to 4 m/sec, which is about half of the conventional speed.

In order to obtain good image quality as a home VTR device, 6.
It is necessary to record and reproduce high-frequency signals near MH2, but at this relative speed of the tape head, the recording wavelength on the tape is extremely short, 0.5 to 0.7 μm.

In such short wavelength recording, the magnetization on the tape self-demagnetizes due to the demagnetizing field, and as a result, the reproduction output is significantly reduced.

To prevent this, a tape with a high coercive force, that is, an alloy tape is used. However, the gap length of the head to enable short wavelength recording/reproduction is 0.2 to 0.3.
In order to magnetize and record a high coercive force tape (Hc > 1000 oersted) with such a narrow gap length, a head core material with a large saturation magnetic flux density (Bs), for example, is required. Sendust alloy (F6-A4-8t alloy), amorphous material (Fe
It is said that it is better to use -Co type). This is because 88 of these materials all have a high value of Bs>8000 Gauss or more.

However, the biggest drawback of Sendust alloy heads and amorphous alloy heads is that they have poor wear resistance and short life.

However, in a head that has a narrow track width and slides on the tape at high speed, such as the above-mentioned small home-use VTR, wear resistance is the most important issue from the viewpoint of longevity and reliability.

On the other hand, in terms of wear resistance, the MH-Z11 ferrite single crystal head currently used as a video head is superior. However, this material 7 material B is 4000~5000G
As shown in Figure 1, a ferrite head with a narrow gap length of about 0.2 μm and a high coercive force tape of, for example, 1300 mm, is used as a recording-only head (2) and a reproducing-only head (1), as shown in Figure 1. Divide into 2 and set the appropriate gap length +31 for each! A combination head with 41 has been proposed.

This means that if the gap length is large, the head can record magnetization on a high coercive force tape even if the magnetic flux density is a little low, while the playback gap should be narrow (for example, 0.2 μm) in order to play back short wavelength magnetization. It is a method.

The present invention relates to a video head with improved performance by improving the Fe2O3 composition ratio and gap length of the combination head.

The present invention will be specifically described below based on embodiments shown in the drawings.

FIG. 1 shows a combination type video head, which includes a playback head (1) and a recording head (f21) as is well known.
are integrated by sandwiching a non-magnetic material (5).

The feature of the present invention is that the gap length (4) of the recording head (2)
is set to be 1.5 to 3 times the gap length (3) of the reproducing head (1).

Radcore (Company) for recording and Radcore (11) for playback
) M nZ n ferrite single crystal was used as the core material in both cases.

In order to set the saturation magnetic flux density (Bs) of the MnZn ferrite single crystal for the recording head to 6000 to 6500 Gauss,
The Fe2o3 composition ratio of the head core is set to 55 mo/% or more and 7Qmo1% or less.

In order to set the saturation magnetic flux density (B5) of the MnZn ferrite single crystal for the read head to 4700 to 5300 Gau8B, the composition ratio of Feze3 in the core of the head is set to 45 mo/% or more and 55 mo/% or less.

It is.

Next, the reason for the above-mentioned numerical limitations will be described regarding an experimental example in a micro-compact VTR.

VTR tape width W inches, head tape relative speed 3
．． 5rrL/see, the tape is alloy powder tape (Hc-
1300 oersted), playback head gap length 0.2
It is μm.

First, regarding the recording head, the larger the gap length, the easier it is to magnetize, and FIG. 4 shows a graph of the relationship between the recording head gap length and the frequency characteristics of the recording/reproducing output.

Recording head gap length is the same as playback head gap length 0
．． At 2 μm, the output is low. The recording head gap length is 0.
In the range of about 4 μm to 0.5 μm, the output increases as the gap length increases, and the frequency characteristics also improve. However, when the gap length becomes 1 μm, low frequency output (for example, I
The output of MH2) improves, but the high frequency output of 6MH2 begins to decrease rapidly. From this, it is preferable that the gap length of the recording head is 0.3 to 0.6 μm. That is, a range of 1.5 to 3 times the read head gap length is appropriate.

In the case of recording video heads, the required magnetic properties of the material include high saturation magnetic flux density, low coercive force, and high permeability. It is more important to have a high

In the case of Mnzn ferrite single crystal, as the composition ratio of Fe2O3 increases, Bs increases, but conversely, the AC effective magnetic permeability decreases. The graph in Figure 5 shows this situation, and this is the graph of Fe 203 in the Mnzn ferrite single crystal.
It shows the relationship between content, saturation magnetic flux density, and magnetic permeability. Here, the effective magnetic permeability is measured using MH2 with each composition ratio.
A ring sample (diameter 2, hole diameter IW+) with a magnetic path plane (1101 plane) was punched out from an n-ferrite single crystal using an ultrasonic processing machine, and then polished to a thickness of 0.2 mm with a formal diameter of 0.04 m. The wire was wound 15 turns and a vector impedance meter was used.The measurement frequency was 5MH2.

As mentioned above, even though more emphasis is placed on the saturation magnetic flux density in recording video heads, in order to convert the recording signal into a large leakage magnetic field at the head gap, the coercive force may be small and the magnetic permeability may be high. This is important and should be decided based on this balance.

Even if Fe 203 is increased by 70m01% or more, Bs (saturation magnetic flux density) hardly increases and on the contrary begins to decrease. On the other hand, since the magnetic flux decreases rapidly, Fezes <70m
0/% or less is required. Also, B8 decreases rapidly as Fe2O3mJ% decreases, but for alloy tapes, the larger the BS, the better at least 6000 Gauss.
The above is necessary.

From this, 65<Fe20a<70 (mob'%
) The reproducing video head material is also required to have a high saturation magnetic flux density and high magnetic permeability like the recording video head material, but high magnetic permeability is more important.

As can be seen from the graph in Figure 5, the content of Fe 203 is 7.
As the magnetic permeability decreases from 0 m1', the magnetic permeability tends to increase, reaches a peak value near 4 amoz, and begins to decrease below that.

On the other hand, Bs gradually decreases as the Fe2O3 content decreases, and its effective range is 45<Fe2O3
<55 (mo/<) is appropriate.

From the above, the core material of the recording head is 65〈Fe20g
<70 (mo/<) Bs'6000 Gauss, and the core material of the playback head is 45 <Fe 203
< 55 (m07%) B+s'5000 Gauss
A so-called combination head using magnetic permeability (m=700 (at 5MH2)) exhibits excellent characteristics as a head compatible with alloy tapes.

Figures 2 and 3 show other embodiments of the combination head, in which the magnetic material (7) is replaced with the non-magnetic material + 5).
! A reproducing head (1) and a recording head (2) are integrated through a pair of elements sandwiched by 51.

In FIG. 3, a reproducing head (1) and a recording head (2) are placed facing each other with a gap between them on a brass base (6).

As described above, in the present invention, the head is manufactured using Mnzn ferrite single crystal, so there is no loss of wear resistance, and the gap length and saturation magnetic flux density are optimally determined for the reproduction head and recording head. It has excellent effects such as high performance.

It goes without saying that the present invention is not limited to the above configuration, and that various modifications can be made within the technical scope of the claims.

[Brief explanation of the drawing]

FIG. 1 is an oblique view of the combination head, FIGS. 2 and 3 are front views of other embodiments of the combination head,
Figure 4 is a graph showing the relationship between the recording rad gap length and the frequency characteristics of recording/reproducing output, and Figure 5 is a graph showing the relationship between Fe2O3 content, saturation magnetic flux density, and magnetic permeability in MnZ and ferrite single crystals. It is. (1)...Reproducing head (2)...Recording head Applicant: Sanyo Electric Co., Ltd.

Claims (1)

[Claims] ■ In a combination video head that combines dedicated heads for recording and playback, the gap length of the recording head is 1.5 to 3 times the gap length of the playback head.
MnZn ferrite single crystal is used as the core material of both the recording head core and the reproducing head core, and the saturation magnetic flux density of the MnZn ferrite single crystal for the recording head is set to 6000 to 6500 Gauss (Fe
The composition ratio of zOa was set to 65 to 70m01%, and the saturation magnetic flux density of the MfiZt17 elite single crystal for the read head was set to 47%.
A combination type video head characterized in that the composition ratio of FezOa is set to 45 to 55 mo1% in order to obtain 00 to 5300 Qaus s. (2) The video head for a high coercive force tape according to claim 1, wherein the gap length of the reproducing head is 0.2 to 0.3 Pm, and the gap length of the recording head is 0.3 to 0.6 μm.