JPS61160818A - Thin film magnetic head - Google Patents

Abstract

PURPOSE:To decrease B-jump noise by forming at least one of yokes which face each other via a head gap part of a high permeability magnetic material having no magnetic wall. CONSTITUTION:The upper yoke 1 formed of a 'Permalloy(R)' sputtered film is set at 0.5-1.0mum film thickness and forms a magnetic path for conducting a magnetic field 3 generated by a recording medium 2 such as magnetic tape to an MR element 4. The element 4 is formed of a 'Permalloy(R)' film deposited by evaporation to 300-500Angstrom film thickness. The length thereof is set at about the length of the track width. A conductor 5 consisting of Al-Cu is disposed to face the lower part of the element 4 in order to apply a bias magnetic field to the element 4. The head gap 6 at the end face of the yoke 1 facing the magnetic recording medium 2 faces the lower yoke 7. The yoke 7 is manufactured of the high permeability magnetic material which does not form a magnetic wall. Said yoke is deposited on a substrate 8. The film of a 'Sendust(R)' alloy, etc. formed to several mum by a sputtering method, etc. is used for the yoke 7.

Description

[Detailed Description of the Invention] Technical Field> The present invention detects signals recorded on a magnetic recording medium using a magnetoresistive element (hereinafter referred to as an MR element) that applies the magnetoresistive effect of a ferromagnetic thin film. It relates to a thin film magnetic head.

<Prior Art> Thin-film magnetic heads that utilize the magnetoresistive effect of ferromagnetic thin films are known to have many advantages over commonly used wire-wound magnetic heads. A thin film magnetic head receives a signal magnetic field generated from a magnetization pattern recorded on a magnetic recording medium and extracts this as a voltage change based on a resistance change of an MR element, so it does not depend on the transfer speed of the magnetic recording medium. This type of magnetic head has the advantage of being able to reproduce a signal without any movement, and that it can obtain a higher output reproduction signal than a wire-wound magnetic head when the transport speed is low.

In actual use, rather than constructing a thin-film magnetic head with a single MR element, the MR element part is separated from the head tip, and a magnetic flux introduction path (yoke) is arranged to guide the magnetic flux generated in the magnetic recording medium to the MR element part. A thin film magnetic head called a normal yoke type MR head (also referred to as a YMR head), which has a structure as shown in Figure 2, is more effective in improving signal resolution and durability of the MR element, and in recent years this type of head has become more popular. It is attracting attention as a fixed head digital audio playback head (8th Japan Society of Applied Magnetics Academic Conference Abstracts (1984) 14PB-111'-Yoke type
(Refer to "Reproduction characteristics of R head").

FIG. 2 is a cross-sectional view of a conventional YMR head in a direction perpendicular to the track width direction. The upper yoke 9 is usually 0.5 to 1.
It is made of a permalloy film with a thickness of about 0 μm, and the magnetic field 11 generated by the magnetic recording medium 10 is transmitted to the MR element! It becomes a magnetic path to lead to 2. The MR element 12 is made of a permalloy vapor-deposited film, and the film thickness is set to 300 to 500 A, and the length is set to about 50 μm, which is the track width. Also, MR element 1
A conductor 13 made of A4-Cu is disposed to apply a bias magnetic field to 2. The head gap 14 is set to about 0.2 to 0.3 μm since the minimum recording wavelength actually used is about 0.5 μm. lower yoke 1
5 is made of a high magnetic permeability magnetic material and is a problem in the present invention. Generally, a polycrystalline NiZn ferrite substrate or a single crystal or polycrystalline MnZn7 elite substrate is used. The track width is usually set to about 50 μm since the YMR head has a multi-track configuration.

In a thin film magnetic head equipped with an MR element as described above, a major problem is the influence of noise peculiar to ferromagnetic materials and distortion of signal waveforms on the S/N ratio of reproduced waveforms. The noise and waveform distortion can be determined using a measuring device as shown in FIG. 3 as output response characteristics of the head similar to the response of the magnetic field from the recording medium. In FIG. 3, I6 is a sine wave oscillator of several tens of Hz, 17 is a current amplifier, 18 is a coil, 19 is a measuring head, 20 is a magnetic field direction perpendicular to the track width direction, and 21 is a sense current source that energizes the MR element. , 22 is the sense current, 23 is a high input impedance inverting amplifier, 24 is a current monitoring resistor that conducts current to the coil, 25 is the X input of the synchroscope, 26 is the Y input of the synchroscope, and 27 is the tube surface of the synchroscope. . The input magnetic field flash and head output (
4) is measured on the synchroscope tube surface 27.
A magnetic field-output characteristic curve as shown in photo) can be obtained. Here, the sense current is 5mA and the amplifier gain is 60dB.

Synchronoscope X is 1divlOOe SY is Idi
vO, 5V.

When a polycrystalline NiZn7z light substrate is used for the lower yoke 15, as shown in FIG. 4, the output exhibits approximately square-law characteristics with respect to the magnetic field, but many discontinuous change points appear in the middle of the curve. This change point is usually the Barkhausen jump (hereinafter referred to as B
-jump) and is the main cause of noise in YMR heads. The relationship between the magnitude of this noise is determined not only by the size of the B-jump in a certain magnetic field but also by the overall B-
It is necessary to determine the magnitude of noise from the size and frequency of jumps. Furthermore, as can be seen in FIG. 4, something like small hysteresis also appears in some parts, but below, this and B-jump are collectively referred to as B-jump noise. When actually reproducing the signal magnetic field from the recording medium, the conductor 13 shown in Figure 2 is energized to generate a bias magnetic field, and the bias magnetic field causes the head to approach a linear response, but the reproduction output changes as shown in Figure 4. B-jump noise appears as points. One of the causes of this B-jump is thought to be that the magnetization within the MR element has a magnetic domain structure and is caused by discontinuous movement of domain walls.

B - To make the jump easier to see, mark the X of the measuring device in Figure 3.
Figure 5 (photograph) shows the results of measurement with input 25 being AC coupled. In the following explanation, the relationship between the magnitude of the small B-jump is a problem, so in the magnetic field-output measurement, the X input 25 is
It is assumed to be C-bonded.

<Object of the Invention> In order to solve the above-mentioned problems, the present invention makes the lower yoke of the MR head from a material in which domain walls are not formed, thereby reducing B - Reduce jump noise and improve S/N
It is an object of the present invention to provide a thin film magnetic head equipped with an MR head having an MR head ratio.

<Embodiment> FIG. 1 is a configuration diagram showing a cross-sectional structure of a YMR head in a direction perpendicular to the track direction, showing one embodiment of the present invention. The upper yoke l made of permalloy sputtered film is set to a film thickness of approximately 0.5 μm to 1.0 μm, and is suitable for magnetic recording media (
This serves as a magnetic path for guiding the magnetic field 3 generated in the magnetic tape (magnetic tape, etc.) 2 to the MR element 4. The MR element 4 is made of a permalloy vapor-deposited film, and the film thickness is set to 300 Å to 500 Å, and the length is set to be approximately the length of the track width (approximately 50 μm). Also, in order to apply a bias magnetic field to the MR element 4, AI! ,−
A conductor 5 made of Cu is arranged below and facing the MR element 4. The helad gap 6 at the end face of the upper yoke l facing the magnetic recording medium 2 is set to about 0.2 to 0.3 μm, and faces the lower yoke 7 with the helad gap 6 interposed therebetween. The lower yoke 7 represents a feature of the present invention, and is made of a high permeability magnetic material that does not form domain walls and is deposited on the substrate 8. In this embodiment, the material of the lower yoke 7 is a Sendust alloy consisting of 3 to 6% by weight of A2, 8 to 12% by weight of Si, and the balance of Fe, which is formed into a film by electron beam or sputtering. is several μm. Note that materials other than the Sendust alloy described above can be used as long as they are magnetic materials with high magnetic permeability that do not form domain walls, that is, do not have a magnetic domain structure.

The magnetic field-output characteristics of the YMR head constructed as described above are shown in FIG. 6 (photo). As is clear from a comparison between FIG. 5 and FIG. 6, it is recognized that the YMR head of this embodiment has smaller B-jump noise.

In addition to the above-mentioned movement of the domain walls within the MR element, the following two causes of B-jump noise in the YMR head can be considered.

+l) B-jump noise due to the input magnetic field within the MR element also responding nonlinearly due to the nonlinear change in magnetization associated with the magnetic domain structure of the upper yoke of the YMR head to the external magnetic field (2) Lower side of the YMR head The nonlinear change in magnetization associated with the magnetic domain structure of the yoke with respect to the external magnetic field causes MR to occur through the shortest distance between the upper and lower yokes around the gap.
This is input to the element as a nonlinear change in magnetic flux, and appears as B-jump noise at the output.

In order to separate the causes of (1) and (2), Curie temperature (
TC) polycrystalline N1= as the lower yoke with 140 °C
While increasing the temperature of the YMR head using Zn ferrite,
The results of measuring the magnetic field-output characteristics are shown in Figure 7 (photo). In Figure 7 (4), Tc = 23℃, and in the same CB), Tc = 63
°C1 (C) is Tc = +15 °C1 (C) is Tc = 1
26″C, % same) is the characteristic curve that appears on the synchroscope tube surface when Tc = I59°C, X (horizontal direction) is Idiv (1 scale), 120eSY (vertical direction) is 1d
It is ivO65v.

From FIG. 7, above Tc, the B-jump noise becomes negligibly small. Above Tc, the lower yoke becomes a mere non-magnetic substrate (paramagnetic material), so the characteristics at that time will be magnetic field-output characteristics that reflect the characteristics of the upper yoke, and the upper yoke will not become a source of B-jump noise. . Therefore, it will be dominated by the cause (2) above.

Here, we will discuss the reason why the B-jump noise is larger in the YMR head using the conventional NiZn ferrite polycrystalline substrate as the lower yoke than in the YMR head of the above embodiment. The average grain size of the NiZn ferrite polycrystalline substrate is about 8 μm, while the width of the upper yoke in the track width direction of the YMR head and the length of the MR element are about 50 μm because it is a narrow track head. Therefore,
There are about six grains (crystal grains) under the upper yoke, and each grain is naturally a single crystal, but it is in a single magnetic domain or multi-domain state. When a magnetic field is applied here, domain wall movement occurs in grains that are in a multi-domain state, causing discontinuous movement of magnetization and the accompanying magnetic field (diamagnetic field).
The minute distance between the lower yoke and the upper yoke is 0.3 μm (
It is thought that the signal is transmitted to the MR element through the head gap) and a B-jump occurs in the output. This situation is the same even when the lower yoke is made of a material forming a domain wall, such as single crystal or polycrystalline MnZn7 elite or permalloy.

YM using the aforementioned polycrystalline NiZn7 elite substrate
The structure is the same as the R head, and the materials are the same except for the lower yoke. Figure 8 (photo) shows the magnetic field-output characteristics when a single crystal MnZn7 elite substrate is used for the lower yoke.
FIG. 9 shows the magnetic field-output characteristics when a permalloy film with a film thickness of 0.6 μm is used for the lower yoke. B-jump noise, which is thought to be caused by the domain wall of the lower yoke, is shown in Figure 8.
Both figures in Fig. 9 are larger than those in Fig. 6 when the lower yoke is made of Sendust film. Further, in this embodiment, as shown in FIG. 1, the lower magnetic material has a structure using a magnetic material having no domain wall, but as shown in FIG. In the case where the B-jump noise is provided on the lower side, the B-jump noise can be reduced by providing the upper yoke 34 with a high permeability magnetic material 34 that does not have a domain wall. still,
In Fig. 1θ, 29 is a magnetic recording medium, 30 is an input magnetic field, and 31
32 is an MR element, 32 is a bias conductor, 33 is a gap portion, 34 is an upper yoke made of a high permeability magnetic material having no domain wall, and 35 is a lower substrate for the high permeability magnetic material.

Next, reduction of B-jump noise and improvement of the quality of the reproduced waveform of a digital magnetic recording medium will be explained by showing a 64 KBPI eye pattern reproduced waveform and a 3 KHz reproduced waveform of the 8/times conversion method.

Figure 1+ (photo) and Figure 12 (photo) are Y of this example.
These are a 3 KHz reproduced waveform and an eye pattern reproduced waveform by the MR head. Figures 13 and 14 show YMR using a conventional polycrystalline NiZn7 elite substrate for the yoke.
These are a 3KHz reproduction waveform and an eye pattern reproduction waveform by the head. In the conventional YMR head, the eye pattern is degraded as shown in FIG. 14 in response to the B-jump seen at No. 1311. On the other hand, in the YMR head of this embodiment, there is no B-jump as shown in FIG. 1I, and therefore the eye pattern is good as shown in FIG. 12.

<Effects of the Invention> As described in detail above, according to the present invention, a narrow track, narrow gap YMR head with low B-jump noise can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a YMR head showing an embodiment of the present invention. FIG. 2 is a sectional view of a conventional YMR head. FIG. 3 is a block diagram of a head magnetic field-output characteristic measuring device. FIG. 4, FIG. 5, and FIG. 6 are explanatory diagrams each showing the magnetic field-output characteristics using photographs of waveforms on the tube surface of an oscilloscope. FIG. 7 is an explanatory diagram showing the relationship between Curie temperature (Tc) and magnetic field-output characteristics using a photograph of an oscilloscope tube surface waveform. FIGS. 8 and 9 are explanatory diagrams showing the magnetic field-output characteristics when a single-crystal MnZn ferrite substrate is used for the lower yoke and when a permalloy film is used, respectively, using photographs of oscilloscope hoop tube surface waveforms. FIG. 1θ is a sectional view of a YMR head showing another embodiment of the present invention. FIGS. 11 and 12 are explanatory diagrams showing a 3 KHz reproduced waveform and an eye pattern reproduced waveform according to an embodiment of the present invention as photographs of oscilloscope tube surface waveforms. Figures 13 and 14 show YM using a conventional polycrystalline NiZn7 elite substrate for the yoke.
FIG. 2 is an explanatory diagram showing a 3 KHz reproduced waveform and an eye pattern reproduced waveform by the R head as a photograph of an oscilloscope tube surface waveform. 1... Upper yoke 2... Magnetic recording medium 3.
...Magnetic field 4...MR element 5...Conductor 6
...Head gap 7...Lower yoke 8.
・・Substrate agent Patent attorney Ai Fukushi (2 others) Figure 3 7) Edict JE to figure

Claims (1)

[Claims] 1. In a thin film magnetic head that includes a magnetoresistive element that is magnetically coupled using a yoke that is formed above or below a head gap and is in contact with a magnetic recording medium as a magnetic path, 1. A thin film magnetic head characterized in that at least one of the yokes facing each other is formed of a high permeability magnetic material having no domain wall.