JPS634444A - Magnetic memory device - Google Patents

Abstract

PURPOSE:To identify the presence of the magnetic domain in a submicron size and to make a magneto optical recording in a high density compared to the conventional method by projecting to a medium the electron beam having higher space resolving power than that of a light as a reading means. CONSTITUTION:The spin of a secondary electron 6 jumping out of the medium by the projection of a primary electron is polarized by the magnetization of the medium, but the polarization degrees differ by the direction of the magnetization and the presence of a crescent magnetic domain, namely the presence of a record pit can be detected if a spin detector is arranged at the prescribed position. The crescent magnetic domain means 0.4mum bit period and 0.2mum magnetic domain width, a polarized spin is 0.2mum space resolving power at its space resolving power and the presence of the magnetic domain is discriminated thereby. The inner part of a vacuum chamber 8 is exhausted upto 5X10<-9>Torr for a reading, for example, and a field emission type electron gun 5 is used at acceleration voltage 4kV and 3nA current value. The discrimination time as to whether a crescent record is made or not actually depends upon the sensibility and weight of the detector 7 detecting the polarization of the polarized spin 6 at high density.

Description

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

[Conventional technology]

Currently, magneto-optical recording is attracting attention as a large-capacity recording device, but in the optical modulation method, which is the mainstream writing method, the limit on the size of the storage bit is 1 μm due to the phenomenon of light diffraction.
There are problems such as slow access times because it is difficult to overwrite information. Recently, early morning Kobayashi et al.
(1984), a writing method using a magnetic field modulation method was studied in order to solve the above problem. This principle is the second
As shown in the figure. Now, consider the case where a rotating recording medium is continuously irradiated with focused laser light. The temperature distribution of the medium irradiated with the beam at the rear of the beam is as shown in FIG. That is, the medium temperature To at the beam end is higher than the Curie temperature Tc (or Neel temperature TN) and as it moves away from the spot, the medium temperature T1. T2 has become lower than Ts and Tc. Temperature T+ (i=o,
1. 2. Coercive force H of the medium at 3°...)
c fr, He t, Hc 1 < Hc 2
<Hcs. Now, H is near the beam spot.
There is a write magnetic field v, and Hcz<Hw<Hc
s, Hc is the magnetic region of HW, that is, Tw in the figure.
The magnetization in the range from Tc to Tc is reversed.

This reversed magnetization region is called crescent recording because it has a crescent shape that is a fraction of the beam spot as shown in the figure. This crescent recording uses a method of writing using a pulsed magnetic field while continuously irradiating a laser beam, so it has the advantage that overrides can be achieved extremely easily, similar to conventional magnetic heads.

[Problem that the invention seeks to solve]

The biggest problem with the above-mentioned crescent moon recording is that the readout method has not yet been developed. In other words, since the recorded bits are reduced to a fraction of the spot size in magneto-optical recording, CN cannot be obtained by optical readout such as the Kerr effect. The purpose of the present invention is to solve this fatal problem and to put it into practical use as a new high-density special memory device.

[Means for solving problems]

The above object is achieved by irradiating the medium with an electron beam, which has a higher spatial resolution than light, as a reading means. Using a field emission type electron gun, it is possible to narrow down the irradiation electron beam to a diameter of approximately 0.1 μm. The spins of secondary electrons ejected from the medium by this primary electron irradiation are polarized by the magnetization of the medium, and the degree of polarization differs depending on the direction of the magnetization. Therefore, by placing a spin detector at a predetermined position, it is possible to detect the presence or absence of crescent-shaped magnetic domains, that is, the presence or absence of recorded bits. An example of the application of this technology is the 9th Japan Society of Applied Magnetics Academic Lecture Abstracts (1985).
On page 55, there is a description as a spin-polarized scanning electron microscope.

Furthermore, the presence or absence of recorded bits can also be detected using the fact that the reflected trajectory of the primary magneton is bent by the electromagnetic force of the magnetization of the medium (Lorentz force).

[Effect]

The crescent-shaped magnetic domain has a bit period of 0.4 μm (0.2 μm in the magnetic domain).
m) Although it could not be easily resolved with a laser beam, polarized spins have a spatial resolution of 0.2 μm. This allows the presence of magnetic domains to be determined, thereby preventing malfunctions. Further, since the electron beam is used for reading only, it requires only a weak current, which has the advantage that the field emission type electron beam source has a long life and that the access time can be shortened because it can be used as a read head edffi.

〔Example〕

Hereinafter, a practical example of the present invention will be explained with reference to FIG. The magneto-optical disk 1 was fabricated by depositing TbFeCo on an epoxy resin substrate. Semiconductor laser 2 (λ=780 nm
, 10mW), write with a bit width of 0.4μm when the media speed is 50α/S? I was able to make it happen. At this time, the beam spot was approximately 3 μm, and the line width of the recording bit of the pit was 6 μm. Here, the writing pulse generating coil 3 has a structure in which a magnetic field of 500e is applied to the disk surface at a QLI when the current of about 1 μH1 pulse is 2A.

Bias magnet 4 is used here to facilitate writing.
A bias magnetic field of 6 i o 00e is applied.

As described above, this device has a pit density of 0.4×1.
High-density writing of 6 μm2 was achieved. I was also able to perform overwriting using the same procedure without any problems.

Next, for reading, the inside of the vacuum chamber 8 was
Exhausted to 10-"l'orr. Field emission type electron gun 5
was used at an accelerated flexural pressure of 4 kV and a current value of about 31'lA.

In fact, it takes 3 x 10" electrons to determine whether or not a crescent moon record is being made, and approximately I
It took Qms. During this time, the detector 7 (MOtt director here) detects the polarization degree of the polarized spin 6 with high sensitivity.
However, it goes without saying that if a highly sensitive and lightweight demon detection device, 5'fJ, is used, detection will be possible in a much shorter time.

〔Effect of the invention〕

According to the present invention, since it is possible to identify the presence or absence of a submicron-sized error, it is more effective in reading from a high-density magnetic recording medium than the conventional method of magneto-optical recording.

[Brief explanation of drawings]

FIG. 1 is a conceptual block diagram of a magnetic memory device according to an embodiment of the present invention, and FIG. 2 is a diagram showing the writing principle. 1... Magnetic recording medium, 2... Semiconductor laser, 3...
- Coil for applying pulsed magnetic field, 4... Coil for bias magnetic field, 5... Electron gun for emitting electric field, 6... Polarized electron,
7...' Frame detector, 8... Vacuum chamber.

Claims (1)

[Claims] 1. In an apparatus having a magnetic thin film for storing information, and at least means for writing information into the magnetic thin film and means for reading information, micro magnetic domains that are carriers of information in the magnetic thin film are modulated by a magnetic field. means for writing in a size smaller than the spot diameter of the focused beam depending on the method, means for irradiating an electron beam to a predetermined position as a means for reading out the magnetic domain, and intensity of reflected electrons or secondary electrons from the predetermined position. A magnetic memory device comprising at least means for detecting.