JPS62239490A - Magnetic memory device - Google Patents

Abstract

PURPOSE:To detect independently a VBL one by one by discriminating the presence and absence of an information carrier with a tunnel current or a discharging current to occur by impressing the voltage between the device close to a prescribed information reading part in a magnetic thin film and the magnetic thin film and reading information. CONSTITUTION:A needle-shaped electrode 8 sharpened sharply from the external part of a magnetic thin film 10 to an information reading part 3 of one edge of a major line 2 is made close to the magnetic thin film 10 without limit, the voltage of about several volts and several tens of the volt is impressed between both, and then, a 'tunnel current' occurs. The size of the tunnel current, when an impressed voltage is constant, is changed by depending upon the work function of an inter-electrode distance, an electrode material and a magnetic thin film material. Thus, the difference in the work function due to the presence and absence of a vertical Bloch line (VBL) pair 6 and the lattice distortion through magnetostriction is sensitively reflected at the difference of the tunnel current and the presence and absence of the VBL pair 6 can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic memory, and particularly to an extremely high-density, large-capacity magnetic memory device.

[Conventional technology]

Recently, as a candidate for a large-capacity memory device using a magnetic bubble material, a Ploch line memory device in which a pair of vertical Ploch lines (VBL pair) existing inside a domain wall is used as an information carrier has been attracting attention. For details, see 1. For example, I.E.E., Transaction on Magnetics,
MAGE-19, (5) (1983) pp. 1838-1840 (IEE, Trans.
Magnetics+MAG19. (1983) pp.
, 1838-1840. That is, in the Ploch line memory, writing is performed by applying a pulsed magnetic field to the ends of striped magnetic domains to cause the ends of the magnetic domains to contract in a short period of time. On the other hand, for reading, the end of the magnetic domain was stretched and the portion containing the VBL pair was cut to form a magnetic bubble. At this time, the VBL pair remains in the bubble and at the same time is replicated to the original striped magnetic field edge. The separated bubbles are then guided to a detector using a magnetic field or current drive method according to conventional bubble technology, and the presence or absence of information is determined by the presence or absence of bubbles. Normally, since the magnetoresistive effect changes depending on the presence or absence of bubbles, the presence or absence of bubbles has been determined by passing a constant current through the detection wire and monitoring the voltage across the wire.

Even if the minor loop, which is the information storage section, is composed of a plurality of rows of striped magnetic domains, the reading section will consist of a major line (or major loop) using bubble rows. Furthermore, due to the chip configuration, a configuration has been proposed in which a striped magnetic domain is arranged as a major loop and the VBL pair of the minor loop is transferred to the major loop and read out, but no consideration has been given to a method for directly reading out the VBL pair. Ta.

[Problem that the invention sought to solve]

In the above conventional technology, (1) when reading out bubbles, the film thickness is made thin in order to coexist bubbles and VBL pairs (for example, film thickness h = 2 μm for stripe domain width w = 5 μm);
The data transfer rate is limited by the movement speed or mobility of the bubble magnetic domain, which tends to reduce the detection output.
The bit density of the read area is about 100 times smaller than that of the VBL pair, which is disadvantageous in terms of high density/large capacity ratio. On the other hand, (2) when using striped magnetic domains in the major loop, there is a problem in that a method for individually detecting VBL pairs has not been developed.

The main object of the present invention is to provide a VBL pair detection method that is particularly effective in the configuration (2).

It goes without saying that this method can be used to detect (1) or a normal magnetic bubble memory.

[Means for solving problems]

The above purpose was achieved using scanning tunneling electron microscopy (ScanningTunneling), which has recently been attracting attention as a method that enables scanning of thin film surfaces with single-atomic resolution.
This is achieved by applying the tunneling current of the two-object question, which is the basis of the Microscpe (STM) method. For an explanation of STM, see, for example, "Science" Volume 15, No. 10.

October 1, 1985, pages 10 to 17.

In other words, when a sharply pointed needle-shaped electrode from outside the magnetic thin film is brought as close as possible to the information readout section at one end of the measuring loop, and a voltage of several volts to several tens of volts is applied between the two, a quantum mechanical phenomenon occurs. ``Tunnel current''
occurs. When the applied voltage is constant, the magnitude of this tunneling current J does not depend on the distance S between the electrodes and the work function of the electrode material and the magnetic thin film material J r"exp (A'l"
12・S). Here A=(4π/h)
(2m)12 (m is electron mass, h is blank constant).

S is the distance between the needle electrode and the thin film, ψ is the potential ■ wall height, and the average value is ψ = - (φ8 + φt) (φ8
; work function of the thin film; φゎ; work function of the electrode). Therefore, the difference in work function due to the presence or absence of the VBL pair and the lattice strain caused by magnetostriction are sensitively reflected in the difference in tunneling current, making it possible to detect the presence or absence of the VBL pair. Here, a major difference between the present invention and STM is that there is no need for a function of scanning the needle-like electrode close enough to the magnetic thin film to generate a tunneling current more than necessary. That is, since the VBL pair transfers at high speed along the major loop, it is sufficient that the needle electrode is placed in a part of the major loop and can move to the extent that it does not deviate from the transfer path of the VBL pair.

[Effect]

The needle electrode is installed so as to be substantially fixed at the readout position.

Since the VBL pair, which is the object to be measured, moves below the needle-like electrode, it becomes unnecessary to scan the needle-like electrode, and this operation does not occur.

Furthermore, tunnel current does not necessarily occur only in vacuum. In addition to being generated in the atmosphere, it is also possible to insert a liquid or solid between the electrode and sample to absorb external vibrations and increase the signal-to-noise ratio.

〔Example〕

The present invention will be explained below with reference to examples.

[Embodiment 1] FIG. 1 shows an example of reading from the Ploch line memory. (a) of the figure schematically shows the configuration of the memory, and (b) of the figure is an explanatory diagram of the tunnel current reading section according to the present invention. A VBL generator is provided at the right end of the striped magnetic domain constituting the major loop 2, and the end of the magnetic domain is contracted in a short time to generate a VBL pair. The VBL pair is stored in the minor loop 5 by the gate 4. When reading, gate 4 is activated again.
The VBL pair is transferred to the major loop through the readout section 3. In the readout section, a needle electrode 8 (curvature radius of 50) is installed in a space 20λ above the path of VBL.

8 is a piezo element 11, 12 that can be moved slightly in the X, y, and z directions.
．． It is fixed at 13. The magnetic thin film 10 in which Ploch lines exist is made of garnet single crystal (SmLuGd) a(F
eAQ) sot □, film thickness 0.4 μm, and striped magnetic domain width 0.5 μm.

The saturation magnetic flux density is 1600 Gauss. garnet 1
An Au thin film 9 with a thickness of 50 mm is deposited on the 0 layer to reduce the tunnel voltage. When the tunnel electrode between 8 and 9 was set to 5V, a tunnel current of 5nA was observed when there was no VBL pair.

It was observed that when the VBL pair approached below the needle electrode, the tunnel current changed by ±3 nA. In reality, the piezo element 11,
12 and 13 are operated by the control unit 14 and the control voltages thereof are monitored.

A feedback signal corresponding to the presence or absence of the VBL pair was given to the piezo element, which enabled the detection of the VBL pair. The striped magnetic domain width in this example is 0.5 μm, and V
The recording density by the BL pair is row IGb/cm2.

[Example 2] FIG. 2 shows an example in which an amorphous metal film is used as a Plochline medium, and here a needle-like electrode 8' is monolithically formed on the medium. 8' does not need to be moved, so VB
It was fixed to the L detection part.

A detector is constructed by using PIQ resin between the layers and embedding a needle-like electrode (made by Tic with a radius of curvature of 20) with a distance S between the electrodes of 10. When the tunnel voltage was 4V, a tunnel current of 10 nA was obtained. As VBL approached, the current changed to a maximum of 15 nA, confirming the detection of VBL.

[Example 3] Fig. 3 shows 80 high permeability Ni-Fe alloy thin films deposited on an insulating Plochline memory medium, and (a) and (c) in the figure show polarity. This figure shows the state of magnetization when VBL with different values reach the bottom of the needle electrode. Immediately above VBL, V is formed in the thin film 18 due to exchange interaction.
Indicates that BL has been magnetically transferred. This 18 made it possible to reduce the tunneling voltage between the two species for generating tunneling current. That is, when there is no 18.

A voltage of 80V was required, but by depositing I8, the tunnel voltage could be lowered to 3V.

[Example 4] In FIG. 4, 500 people deposited a high magnetostrictive material T b Fe 2 polycrystalline alloy thin film 22 on a Ploch line memory medium. Transcription VBL similar to Example 3 occurs in 22, but
At this time, due to the magnetostrictive effect, slight elastic irregularities were created in the areas where magnetization is repelled and attracted. In this example, it was found that unevenness of 0.5 to 1 person was generated in the vertical direction on the film.

A needle-like electrode was placed 15λ above the VBL end where the unevenness occurs, and 4V was applied between both electrodes, resulting in a tunnel current, and VBL could be detected by the change in tunnel current corresponding to the unevenness. Next, the electrode 8 is attached to the thin film 22 to 20
0 people were separated. A tunnel current no longer occurred, but a discharge current occurred as a result of applying 60 V between the electrodes. Feedback was applied using a piezo element to keep this discharge current constant, and as a result of monitoring the feedback current, a feedback current corresponding to VBL was observed, similar to the change in tunnel current. The distance was about the same as the size of VBL.

〔Effect of the invention〕

According to the present invention, since each VBL can be detected independently, it is possible to realize an ideal Ploch line memory in which both the minor loop and the major loop have striped magnetic domains. It goes without saying that conventional bubble detection can be performed extremely easily using this detection method.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the chip configuration and tunnel current readout of Example 1, FIG. 2 is a schematic cross-sectional view of the detection section of Example 2, FIG. 3 is a schematic cross-section of the detection section of Example 3, and FIG. 2 is a schematic cross-sectional view of a detection section of Example 4. FIG. DESCRIPTION OF SYMBOLS 1... VBL generator, 2... Major loop (striped magnetic domain), 3... Detection section, 4... Gate, 5... Minor loop (striped magnetic domain), 6... Proch line pair (
VBL pair), 7... Tunnel current JT, 8... Acicular electrode, 9... Au thin film (sample electrode), 10... Magnetic thin film (garnet single crystal), 11.12.13...・Piezo element OC+'/+Z direction), 14... Control unit, 15... Magnetic thin film (
amorphous GdCoMo alloy), 16-PIQ resin, 17... pad for sample electrode, 18... high magnetic permeability metal film. 19 a, c-VBL", transferred magnetization of VBL-. 19b... Transfer magnetization of Bloch wall, 20... VBL
Traveling direction, 21... Bloch wall, 22... High magnetostrictive material. 23... Lattice distortion due to VBL.

Claims (1)

[Claims] 1. A magnetic memory device comprising a magnetic thin film for storing information and at least means for writing and reading information into the magnetic thin film, wherein an information carrier in the magnetic thin film is provided. is a magnetic domain or domain wall, and in a structure in which the information carrier is transferred in the magnetic thin film by an electromagnetic field applied from the outside, there is a voltage between the magnetic thin film and a device close to a predetermined information reading section in the magnetic thin film. A magnetic memory device that reads information by determining the presence or absence of an information carrier based on a tunnel current or discharge current generated by applying a current. 2. The magnetic memory device according to claim 1, wherein at least one of a metal film, a soft magnetic film, and a high magnetostrictive film is deposited on at least a portion of the surface of the magnetic thin film. .