JPS60223043A - Micro magnetic head - Google Patents

Abstract

PURPOSE:To obtain a micro magnetic head which can control the direction of magnetization within a magnetic domain in a magnetic thin film, by applying a bias magnetic field to the head. CONSTITUTION:A micro head core 11-1 consisting of a magnetic thin film is magnetized by a signal magnetic field given from a recording medium. Then a bias current 13-2 is flowed to the core 11-1 together with application of a magnetic field higher than an anisotropic magnetic field. Thus the head magnetization is saturated evenly in the axis direction 15-1 easy for magnetization. Under such conditions, a right-turned magnetic field 15-2 leaked out of a recording medium is applied to set the bias magnetic field at zero. Thus a magnetic domain of the head tip part has the right-turned magnetization. While said magnetic domain has left-turned magnetization if a left-turned magnetic field 15-3 leaked out of the recording medium together with the bias magnetic field set at zero. Thus the direction of magnetization is controlled within the magnetic domain at the head tip part and then reproduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a small magnetic head for reproducing ultra-fine recording bits on a magnetic recording medium.

(Prior art) Progress in improving the characteristics of magnetic recording media has been remarkable in recent years.
Recording density is increasing at a rate of about 10 times per year.

In particular, when a perpendicular magnetic recording medium is used, the influence of the demagnetizing field between recording bits is reduced in principle, so ultra-high density recording is possible. A linear recording density of 8,000 bttAran has already been confirmed by Professor Iwa's research group at Tohoku University using a Co--Cr sputtered film and an auxiliary magnetic pole type single-pole head.

However, this value was detected through highly sensitive amplification in the laboratory, and from a practical standpoint it is still 3.000 bi.
The limit of recording density is about t/im. The technical directions for realizing high-output, high-density recording and reproduction are: ■ Improving the residual magnetization of the magnetic recording medium; ■ Developing a mechanism to stably maintain the distance between the head and the recording medium in the submicron range; ■ Increasing the height of the head. Research is continuing in each field to increase sensitivity; etc. Considering that the current perpendicular media still has a lot of potential for recording density, it is thought that the limit for increasing density lies mainly in the head. The problems with the current head are described below.

(1) Single-pole head The single-pole head developed by Professor Iwasaki of Tohoku University is shown in Figure 11 as the head that currently exhibits the highest recording and reproducing characteristics. 1.1 is the main magnetic pole, 1.2 is the auxiliary magnetic pole, 1.3 is the coil, 1.4 is the perpendicular recording medium such as Co-Cr, 1.5 is the base, and 1.6 is the thickness of the main magnetic pole. be. The regeneration principle is as follows.

In other words, the main magnetic pole (1
, 1) The tip is magnetized and leakage magnetic flux from the main pole is detected by the coil (1, 3) K wound around the auxiliary pole (1, 2). In this case, the main magnetic pole (1, 1), which has a smaller leakage magnetic field from the recording bit, needs to be in contact with the recording medium, and the thickness of the main magnetic pole (1, 1) is about the bit size (
0,2 to several 1 trn), so in order to sense that magnetic flux, the distance between the auxiliary magnetic pole (1,2) and the main magnetic pole must be several tens of μm.
The recording medium (1,4
The base (1', 5) of ) must be flexible and thin. Therefore, this type of head has conventionally been used only for floppy disks. Although floppy disks are used for simple purposes, they cannot be used for high-density recording that also requires position control in the track direction.

Hard disks suitable for this purpose have a substrate thickness of 1~
Since it is as thick as 2 days, a single pole head has a disadvantage in that it has poor recording and playback sensitivity and cannot be used.

(2) MR head A diagram of the principle of the MR head is shown in FIG. 2.1 is a magnetoresistive element made of a permalloy film or the like, and has a thickness of L1, a width of W1, and a length of L. 2°211-1: A conductor formed at both ends of the element. The electrical resistance R of the element 2.1 is varied by the signal magnetic field from the medium 1.4. When a constant current (2) is caused to flow through the conductor 2.2, the electrical resistance changes due to the signal magnetic field from the recording medium 1.4, and the voltage across the element 2.1 changes. By detecting this change, it is used as a playback head.

Detailed analysis of MR heads is provided by Ampex's RoP, Hu
nt (Reference IEEE Tran
s, onMag, Vot, MAG-7, super pp 150
~1541971) Output voltage v is (1-e)/kW
is proportional to. However, =2x/, 1 is required, and λ is a recording wavelength corresponding to twice the recording bit length. According to this, when the recording wavelength λ is made small, the element width W needs to be made small in order to secure the output voltage. For example, λ=0.
In order to detect a signal from a 2 μm bit, the element width W
It is necessary to make the length submicron, which is not realistic when considering the element manufacturing and head wear. As described above, the Quizo MR head shown in FIG. 2 has a width loss, but this is because the magnetic circuit is an open magnetic path.

In order to improve this property, a method has been proposed in which a magnetic flux suction port is provided at the back of the MR element and the element is used as part of a closed magnetic circuit. (IEICE Magnetic Recording Research Group MR8
2-24) A diagram of this principle is shown in FIG. 3.1 is a magnetic flux return path made of magnetic ferrite or the like, and 3.2 is a non-magnetic part made of glass or the like. MR element (2)
, 1) returns to the recording medium through the return shaft (3, 1) at the back.

An MR element with a width of 20 μm is used to detect the output of a 0.13 μm wide bit. However, this value is relative output -45d
The reproduction bit length when the output is halved with the value B is as large as 127 μm. Furthermore, in this case, the magnetic tape, which is a recording medium, and the tip of the MR head are in contact with each other, and when the medium and head are separated, the output decreases significantly. If the recording medium and the head tip are l apart, the output will be e times,
For example -ni/l.

If the bit is separated by 0.1 μm, the output decreases by 0.04 times, making it impossible to reproduce even with the improved MR head described above.

The magnetic field Hy in the perpendicular direction from the medium 1.4 that is perpendicularly recorded as shown in FIG. 4 is expressed as Hy=2πMre dy(Oe) (1). However, assuming that Mr is the residual magnetization d of the medium equal to the bit width and the thickness t of the medium is sufficiently larger than the bit width d, the thickness loss of the medium is ignored. FIG. 5 shows the relationship expressed by equation (1). However, Mr = 101000e/cc.

(3) Figure 6 shows a diagram of the principle of magneto-optical reproduction. 6.1 is a light source such as a semiconductor radar,
6.2 is a polarizer, 6.3 is a beam striper, 6.4
is an analyzer, 6.5 is a photodetector such as a photodiode,
6, 6 is magnetization within the recording medium. The light emitted from the light source 6.1 is converted into linearly polarized light by the polarizer 6.2.
4. The plane of polarization of the reflected light is rotated due to the magneto-optic effect. This is passed through an analyzer 6.4 to a photodetector 6.4.
When light is received at 5, the intensity of the light changes depending on the direction of magnetization 6.6, and is detected as a change in output voltage. In this case, the identification resolution of the recorded bits is determined by the diffraction limit of the light beam.Currently, if a semiconductor laser with a wavelength of 0.8 mm is used, the diffraction limit is about 0.4 μm. In order to increase the resolution,
It is necessary to develop a compact light source with a very short wavelength.

(4) Transfer head (Reference: Yamada, Himuro, Makino, "Magnetic recording and reproducing system using garnet film", Institute of Electronics and Communication Engineers, Magnetic Recording Research Group MR79-11) A diagram of the principle of the transfer head is shown in FIG. 7. 7.1 is a soft magnetic film such as garnet or permalloy,
7°2 is the magnetization in the soft magnetic film, and 7.3 is the leakage magnetic field from the medium 1.4. The regeneration principle is as follows. The soft magnetic film 7.1 is magnetized by the leakage magnetic field 7.3 from the recording medium 1.4, and the magnetization 7.2 of the soft magnetic film is detected using exactly the same principle as the magneto-optical reproduction described above. It will be called a transfer head because it partially transfers information from the recording medium 1.4 onto a soft magnetic film. This head has the advantage of reducing media noise because it does not directly irradiate light onto the recording medium, but it is still subject to limitations such as the identification resolution of recording bits or the diffraction limit of light.

Therefore, in this type of configuration, the reproduction limit is about 0.5#1 bit. A proposed modification of the transfer head is shown in FIG. 8.1 is an antioptic membrane, and 8.2 is a light. (Reference, Japanese Patent Publication No. 56-33781) In this case, the soft magnetic film (7°1) is placed upright against the surface of the recording medium (1, 4) like an MR element, and as shown in FIG. Shorter wavelength reproduction is more prevalent than in the evening 1st episode. However, when the recording wavelength becomes shorter, the distance from the medium (1, 4) surface is y,
The leakage magnetic field from the medium becomes small as shown in FIG. 5.

Therefore, for example, if the distance between the head and the medium is 0.1 .mu.m for a 0.1 .mu.m bit, the change in magnetization at the tip of the head will be extremely small, as described in the section on the MR head.

Furthermore, in the case of optical detection, if the time when the magnetization of the soft magnetic film 7.1 is saturated in a certain direction is defined as 1, the magnitude of magnetization is only detected at most 1/100 of the saturation magnetization, taking into account the shot noise of the detector. Can not. For MR heads, it is 1/100.
Although it can detect up to about 0, the sensitivity is low. Furthermore, in the configuration of FIG. 8, no measures have been taken to irradiate the light onto a region within the tip of the soft magnetic film (5.degree. 1), and therefore it is impossible to detect particularly small bits on the order of submicrons.

An example of a similar transfer head is U.S. Pat.
8, the principle diagram is shown in Fig. 9. 9.1 is an optical fiber, 9.2 is a core, and a soft magnetic M7.1 is formed at the tip of the optical fiber 9.1.

The diameter of the core (9,2) of the optical fiber (9,1) is several μm
With this method, the problem with the configuration of FIG. 8 can be solved because the light can be easily focused on a region of about the diameter of the core on the soft magnetic film. however,
No consideration is given to signal detection when the recording bit becomes smaller and the leakage magnetic field becomes smaller. Furthermore, although this type of signal is detected by changes in the plane of polarization of light, no consideration is given to disturbances in the plane of polarization when light propagates within an optical fiber.

As described above, it is difficult for the various heads devised up to now to reproduce with high efficiency, especially minute recorded bits of 1 μm or less, for various reasons. As a method for solving this problem, there is a Japanese Patent Application No. 57-124317 (Micro Magnetic Head), the principle of which is shown in FIG. 1
0.1 is a micro head, 10.2 is a polarization preserving single mode leading waveguide, 10.3 is a core, 1O04 is a polarized light, 1
0.5 is a recording bit. This detects the magnetic field from the medium (1, 4) using a herad core and converts it into a signal by polarizing 10°4. According to this Spatula F, the size of the core (10, 1) can be reduced to the core diameter (several μm), and the efficiency of sucking magnetic flux from the medium can be greatly improved, and the head faces the medium (1, 4). It has characteristics such as being able to detect head magnetization information near the tip, and using an optical waveguide with polarization preservation properties, so there is no signal disturbance within the optical waveguide, making it suitable for high-sensitivity detection of minute signals. ing. However, as can be seen in Figure 5, when the medium and head are in contact, the Herad core can sense the strong magnetic field on the medium surface, but when there is a distance between the medium and the head, the recorded bits are The strength of the signal magnetic field becomes extremely small when it is as small as microns, and it becomes increasingly difficult to configure a head for its detection. For example, if the head flying height is 02 μm, it is 0.2 to 0 from the head tip.
．． The head is sufficiently magnetized only by about 3 μm.

The size of the core should be 02 to 0.3 μm and 8 degrees, but it is difficult to introduce light into an area of this size, so it is necessary to use a high-power laser or standardize only the light input end of the optical waveguide. It is necessary to take measures such as increasing the core diameter by decreasing the relative refractive index difference between the core and the cladding while keeping the frequency at 2.4.

That is, according to Japanese Patent Application No. 57-124317, it is theoretically possible to detect signals from minute bits even if there is a head flying height, but the method of construction thereof becomes increasingly difficult.

As a technique to improve the above-mentioned drawbacks, the present applicant previously proposed Japanese Patent Application No. 58-87557 (Micro Magnetism).This technique uses a magnetic material with a single magnetic domain structure, so it has the problem of being difficult to manufacture. There is.

(Problems to be solved by the invention) In order to solve these drawbacks, the present invention relates to a micro magnetic head characterized by applying a Paianu magnetic field to the head, and its purpose is to record bits of high recording density with high sensitivity. , provides a head with a multi-domain structure that reproduces at high output, and its features include a single mode optical waveguide with polarization preserving properties and a magnetic field formed in a plane intersecting the optical axis of the optical waveguide. It has a magnetic thin film with a multi-domain structure having an optical effect and a conductor in contact with the magnetic thin film, the magnetic thin film has a uniaxial easy magnetization axis, and a magnetic field and a recording medium are generated by a current flowing through the conductor. Due to the leakage magnetic field,
The present invention provides a micro magnetic head that controls the magnetization direction within magnetic domains in the magnetic thin film.

(Structure and operation of the invention) FIG. 1 is a schematic structural diagram of the present invention. Reference numeral 11-'1 represents a micro head core, and 11-2 u represents a current conductor pattern for generating a bias magnetic field. 11-3 is incident light, 11=4
is reflected light, 11-5 is a substrate, and 10-3 is a core of a single mode optical waveguide having polarization preserving property as shown in FIG. Further, the head core 11-1 is a magnetic film having a multi-domain structure and is in contact with the end surface of the optical waveguide 10-3 as shown by the arrow.

It is assumed that the recording medium moves relatively in the core width direction (direction of arrow ■ in the figure). FIG. 12 shows a conceptual diagram for actually operating this head. 12-1 is a light source such as a semiconductor laser, 12-2 is a power supply lead wire, 12-3 is a polarizer, 12-4 is an analyzer, 12-5 is a photodetector such as a photodiode, and 12-5 is a photodetector such as a photodiode. Lead wire for signal detection, 12-
7 is a power source for bias, and 12-8 is a lead wire for introducing current. Note that the recording medium moves in the width direction of the head as shown by the dotted line at 1-4. The reproducing method for the head of the present invention is as follows. The signal magnetic field from the recording medium magnetizes the micro head core 11-J, which is made of a soft magnetic thin film such as alloy, copal, zirconium, or sendust. On the other hand, the light emitted from the light source 12-1 becomes a single polarized wave by passing through the polarizer 12-3, and this light passes through the core 10-3 of the single mode leading waveguide and hits the head core 11-1.

An appropriate incident angle αfd for light to enter the herad core is about 60 to 70°. The plane of polarization of the reflected light 11-4 is rotated by the magneto-optic effect (in this case, the Kerr effect). The direction of rotation differs depending on the direction of magnetization of head core 11-1. By passing this reflected light 11-4 through an analyzer 12-4, the transmitted light changes in intensity depending on the direction of magnetization, and is converted into a stain signal by a photodetector 12-5. Take it out from the lead wire 12-6. It is the same as in Japanese Patent Application No. 124317-1985 that the efficiency of sucking up the magnetic flux from the recording medium is greatly improved by making the size of the head core about the same as the core size of an optical waveguide, and that the magnetization of the head core is detected by light. . Next, the present invention will be explained in detail.

13 and 14 are diagrams for explaining the present invention in detail. FIG. 13 is a perspective view of the head, and FIG. 14 is a view of FIG. 13 viewed from the direction B. 13-1 is the easy magnetization axis of the head core 11-1, 13-. 2 is a current for generating a bias magnetic field, 13
-3 is a bias magnetic field generated by the current 13-2. The operating principle of this head is as follows. The axis of easy magnetization 13-1 of the head core 11-1 is made in the width direction of the head core. Methods for introducing the easy axis of magnetization include applying heat treatment without applying a magnetic field in the desired direction, or increasing the length in the easy direction by increasing the width (Wjj) in the direction perpendicular to it to create shape anisotropy. .

A conductor made of a thin film of copper, aluminum, beryllium copper, or the like is fabricated in contact with such a head core, as shown in FIG. Head core 11 made of magnetic material 9
Although it is not necessary to particularly insulate between -1 and the conductor, inserting an amorphous film of SiO, 5i02, SiN, etc. between them improves the soft magnetization characteristics of the magnetic film that is the head core.

Figure 14(a) shows the magnetization state in the herad core when a bias current is applied and a magnetic field higher than the anisotropic magnetic field is applied, and the magnetization is uniformly in the direction of the hard magnetization axis (14-1 )
is saturated with In this state, when the bias current is reduced to zero, the magnetic domains in the head core have the structure shown in FIG. 14(b) but not in FIG. 14(c). In this way, when the bias current is set to zero, the magnetization direction within the magnetic domain of the head tip can take only two directions: rightward as shown at 14-2, or leftward as shown at 14-3. In an ideal head core without anisotropic dispersion, the direction of magnetization within the magnetic domain is determined by the direction of the infinitesimal external magnetic field at the moment the bias magnetic field becomes zero.

Therefore, if a bias magnetic field is applied to the Herad core in the recording medium leakage magnetic field] 1-1, and then the bias current is made zero, if the direction of the recording medium leakage magnetic field is to the right (14-
4), the magnetization direction in the magnetic domain of the head tip is rightward (14
-2,) 9, the direction of the recording medium leakage magnetic field is to the left (1
In the case of 4-5), the magnetization direction within the magnetic domain of the head tip is leftward (14-3). Figure 14 (d), , + (
This is shown in e). The principle of the present invention is to make the magnetic domain width in the head length direction at the tip of the head greater than or equal to the core thickness of the optical waveguide, and to detect left and right magnetization changes within this magnetic domain using the magneto-optic effect.

9 In the method described above, the axis of easy magnetization of the micro head core is set in the width direction of the head core.

The method of the present invention is also effective when the axis of easy magnetization is set in the head length direction. This will be discussed next.

FIG. 15A shows the state of magnetization in the core when a bias current (13-2) is applied and a magnetic field higher than the anisotropic magnetic field is applied. Magnetization is uniformly in the easy magnetization axis direction (] 5
-1). In this state, a rightward recording medium leakage magnetic field (15-2) is applied, and after the bias magnetic field becomes zero, the magnetic domain at the head tip becomes
), it has rightward magnetization. Furthermore, when a leftward recording medium leakage magnetic field 15-3 is applied and then the bias magnetic field becomes zero, the magnetic domain at the head tip becomes
), it has leftward magnetization. Detecting this left and right magnetization change using the magneto-optic effect is the same as in the case of FIG. 14.

This method controls the magnetization direction within the magnetic domain of the head tip by the direction of the infinitesimal recording medium leakage magnetic field applied to the head tip and reproduces this, making it an excellent high-sensitivity head. I understand.

Next, an example of an actual head will be shown.

An optical waveguide was fabricated on a 5t02% quartz substrate with a thickness of 6 μm and doped with Ge by the VAD method.

The relative refractive index difference with the quartz substrate was set to 0.23%. The waveguide pattern shown in FIG. 12 was formed on this glass film using Ti, and the area other than the area covered with the Ti mask was removed by sloping in a C2F6+c2H4 gas atmosphere to fabricate an optical waveguide. After that, after removing the Ti mask, S r
A 02 film was formed on the entire surface including the turns to protect the waveguide.

The end face of the substrate was optically polished at the bent point of the fabricated optical waveguide, and a microhead was fabricated on this end face using film fabrication method B (RF sputtering and ion beam sputtering), electron beam exposure, and sputter etching. . The membrane was made of 80'at% Ni-Fe permalloy, and Hc was 0.
It became 60e. The head size is 0.2 μm thick and 5 wide.
The length was 50 μm.

The width of one magnetic domain in the head length direction at the tip of the head is the tip! The thickness was 1110 μm, which was more than the core thickness of the optical waveguide (6 μm). The conductor for applying bias current is
It is made of Cu and has a width of 20 μm and a thickness of 11 tm. Next, the surface including the optical waveguide was lightly polished to smooth the surface, and a head was manufactured. An AlGaAs laser diode with a wavelength of 0.78 μm was used as a light source, a Durham-Thomson prism was used as a polarizer and an analyzer, and a Si photodiode was used as a detector.

Coupling of light to the waveguide was performed using a microhead. As a magnetic recording medium, a permalloy film and a Co--Cr film were sequentially formed on a polyimide base having a thickness of 30 mm by sputtering. Each thickness is permalloy 0
．． 3 μm, Co-Cr 0.311 m. FIG. 16 shows a waveform obtained by reproducing recorded bits of a floppy disk using this microhead.

The envelope of the high frequency sine waveform is the signal waveform. Note that a single pole head excited by an auxiliary magnetic pole was used for recording. Bias current is 100 kHz % 100'mArm5
is an alternating current.

The above method uses an alternating current bias magnetic field with a frequency higher than the signal frequency, but a method using a /'P pulse magnetic field synchronized with the signal frequency may also be considered.

In this embodiment, the bit width is 58 m and the track width is 0.
2μm, recording density 10'bit/
Enabled playback of rrrm2.

(Effects of the Invention) As described above, when the head of the present invention is used, submicron-sized bit signals of a recording medium recorded at high density can be detected with high sensitivity. Therefore, by using it as a magnetic head in magnetic tapes, floppy disks, magnetic disks, etc., ultra-high density recording and reproduction is possible. It is thought that the density characteristics can be greatly improved, and it will also greatly contribute to the miniaturization and cost reduction of recording devices.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a head according to the present invention, in which 11.1 is a helad core, 11.2/'i conductor, 11. , l; l: incident light, 11.4 is reflected light, '11.5 is the substrate. Figure 2 shows a conventional magnetoresistive (MR) head.
l'i magnetoresistive element, 2°2 is a conductor, FIG. 3 shows a conventional improved MR head, 3.1 is a magnetic flux return path, and 3.2 is a non-magnetic part. FIG. 4 is a diagram showing a model for calculating the magnetic field on a perpendicular recording medium. FIG. 5 shows the distance dependence of the perpendicular magnetic field Hy calculated based on the model of FIG. 4 from the medium, where the parameter is the bit width. FIG. 6 is a diagram showing the principle of conventional magneto-optical reproduction. 1 is a light source, 6.2 is a polarizer, 6.3 is a beam sinter 16, 4 is an analyzer, 6.5 is a photodetector, 6. .6 is the magnetization within the recording medium. FIG. 7 is a diagram showing the principle of the transfer head. 7.1 is a soft magnetic film for transfer, 7.2 is the magnetization of the soft magnetic film, and 7.3 is a leakage magnetic field from the medium. FIG. 8 shows an example of an improved transfer head, in which 8.1 is a reflective film and 8.2 is a light beam. FIG. 9 shows another example of the transfer head, in which 9.1 is an optical fiber and 9.2 is a core. FIG. 10 is a block diagram of a conventional micro magnetic head.
゜1 is a micro head, 10.2 is a polarization preserving single mode optical waveguide, 10.3 is a core, 10.4 is a polarized light, 10
．． This is a 5u recording bit. FIG. 11 shows a conventional auxiliary magnetic pole excitation type single pole head for perpendicular recording, and shows j), 1.
1 is the main magnetic pole, 1.2 is the auxiliary magnetic pole, 1.3 is the coil, 1
．． 4 is a recording medium, and 1.5 is a base for the recording medium. FIG. 12 is a conceptual diagram of the entire head of the present invention, and 12.1 is a light source;
12.2 is a lead wire, 12.3 is a polarizer, 12.4 is an analyzer, 12.5 is a photodetector, 12.6 is a lead wire, 12
．． 7 is a bias power supply, and 12.8 is a lead wire. Figure 13, diagram of the head for detailed explanation of the invention, Figure 14
(a) to (,) are views of FIG. 13 viewed from the direction B. FIG. 15 is a view seen from direction B in FIG. 13 when the axis of easy magnetization of the head core is in the head length direction. FIG. 16 shows waveforms reproduced by the head of the present invention. Patent applicant Nippon Telegraph and Telephone Public Corporation Patent agent Megumi Yamamoto - Figure 8 Figure 9 e), b IA AlO2fi Figure 11

Claims (1)

[Claims] A single mode optical waveguide having polarization preserving property, a magnetic thin film having a multi-domain structure having a magneto-optic effect formed in a plane intersecting the optical axis of the optical waveguide, and a conductor in contact with the magnetic thin film. and the magnetic thin film has a uniaxial easy axis of magnetization,
A micro magnetic head characterized in that the direction of magnetization in the magnetic domains in the magnetic thin film is controlled by a magnetic field caused by a current flowing through the conductor and a leakage magnetic field generated by a recording medium.