JPS62298084A - Magnetic memory element - Google Patents

Abstract

PURPOSE:To stabilize a Bloch line pair by directly sticking a prescribed ferromagnetic body film to a stripe domain holding layer surface and locally changing the film thickness along a stripe domain magnetic wall. CONSTITUTION:On the surface of a stripe domain holding layer 1, a ferromagnetic body film 2, in which a magnetic wall mobility is different compared with the ferromagnetic body, is directly coated. Then, when a pulse bias magnetic field is added and a magnetic wall is shifted, a gyroscopic force to function at a Bloch line VBL in the magnetic wall is different for the holding layer 1 and for a coating layer 2, an exchange interaction energy is stored at the border of both parties. For this reason, a VBL avoids the condition. Then, when the film thick of the coating layer 2 is locally changed along a stripe domain wall 4, a VBL pair of stabilized to the place where the film thickness of the coating layer 2 is smaller.

Description

[Detailed Description of the Invention] Detailed Description of the Invention (Field of Industrial Application) The present invention provides a non-volatile ultra-high density solid-state magnetic memory element 1-Meiichito (Prior Art) A high-density solid-state magnetic memory element. To this end, magnetic bubble elements have been developed for some time. However, with the currently used garnet materials, the minimum attainable bubble diameter is said to be 0.3 pm. Therefore, a bubble material that retains bubbles with a diameter of 0.3 pm or less must be found other than garnet material. This is not easy and is even considered to be the limit of bubble density.

We have developed an ultra-high-density solid-state magnetic memory element that significantly improves the density limit based on the characteristics of the bubble retention layer and can maintain information readout time at the same level as conventional elements. A Bloch line pair (consisting of two perpendicular Bloch lines that exist statically and stably within a Bloch domain wall that forms the boundary of a striped domain formed in a ferromagnetic (including ferrimagnetic) film with an easy magnetization direction) An element using VBL pairs (hereinafter referred to as VBL pairs) as a memory unit was invented (Japanese Patent Application No. 182346/1982).

One of the most important parts of this device is the information VB
The VBL pairs are stabilized within the striped domain wall in the form of L pairs, and the VBL pairs are transferred within the Bloch domain wall as necessary.

Regarding the VBL stability maintenance method, please refer to the patent application No. 57-0658.
26, by locally changing the direction of magnetic anisotropy in the film plane along the Bloch domain wall around the striped domain that constitutes the minor loop, VBL pairs stably exist along the striped domain domain wall. It has been shown that it is possible to create a position where it does and a position where it does not.

(Problems to be Solved by the Invention) The specific method for locally changing the direction of magnetic anisotropy in the film plane described in Japanese Patent Application No. 58-065826 is 1.
) Utilizing the inverse magnetostriction effect based on lattice strain caused by selective ion implantation into the film, or 2) Forming a pattern on the surface of the striped domain holding film using a material with large internal stress to give stress distribution to the film. , an IEE transaction using the inverse magnetostriction effect based on it.
on Magnetics (IEEETransaction
on Magnetics) Vol, MA
G-20, No, 5pp1135-1137 (1984
) etc. In 1), the direction of the in-plane magnetic anisotropy of the film is controlled only in one part of the film surface. This local change in the in-plane magnetic anisotropy hardly changes the moving speed of the domain wall, and is a method of simply controlling the difficulty of VBL pairing. Therefore, there is no problem if the in-plane magnetic anisotropy is controlled uniformly over the film thickness direction, but the in-plane magnetic anisotropy is changed only in a part of the film, and there is no ion-implanted surface layer. If the boundary between the layers is clear, the gyroscopic force generated for a given domain wall movement speed is constant, so the movement of the VBL pair will inevitably change depending on the difficulty of the movement of the VBL pair. The film becomes non-uniform along the thickness direction. As a result, in some cases, VBL may be separated in the middle of the film thickness, and VBL
This may lead to the disappearance of L pairs. This poses a serious problem in terms of device reliability. In order to eliminate this obstacle, it is desirable to implant ions uniformly in the film thickness direction, but this is quite difficult due to the essential characteristics of the ion implantation method or the performance of the ion implantation device. In method 2), the in-plane magnetic low anisotropy changes more slowly in the film thickness direction than in method 1), and the probability of instability when the VBL pair moves is smaller than in method (1). However, the trend is the same as that of ion implantation.

The purpose of the present invention is to provide a VB that eliminates such conventional problems.
An object of the present invention is to provide an ultrahigh-density recording element having a striped domain domain wall subjected to the L-pair stabilization method.

(Means for solving the problem) That is, the present invention has an information reading means, an information writing means, and an information storage means. A vertical Bloch line pair consisting of two adjacent perpendicular Bloch lines formed in a Bloch domain wall at the boundary of a striped domain in a film (including a body membrane) is used as a storage information unit, and the vertical Bloch line pair is In an element having means for transfer within a Bloch domain wall, another type of ferrimagnetic material is directly applied to the surface of the striped domain retention layer.
A magnetic memory element is presented which is characterized by locally changing the nine haze and blur in the following directions.

(Function) The present invention has shown that by employing the above-described configuration, VBL pairs, which are information units, can be stably held and transferred along the stripe domain magnetic wall. The principle of the present invention will be explained in detail below. As shown in FIG. 3, when the surface of the striped domain holding layer 1 is coated with a ferromagnetic film 2 having a domain wall mobility pw different from that of the ferromagnetic material, when a pulse bias magnetic field is applied to move the domain wall. , V in the domain wall
Since the gyroscopic force acting on the BL is different between the striped domain retention layer and the coating layer, exchange interaction energy is stored at the boundary between the striped domain retention layer and the coating layer. Therefore, VBL tries to avoid that situation. Therefore, when the thickness of the coating layer is locally changed along the stripe domain domain wall, the VBL pair is stabilized where the coating layer thickness is small. FIG. 1 shows how the film thickness is varied in the striped domain domain wall portion in the present invention. The VBL pair 6 in the domain walls (Bloch domain walls) on both sides of the stripe domain 3 is stabilized in the thin film thickness portion.

This is because the VBL has a higher energy density than the surrounding Bloch domain walls, so it is likely to be stabilized where the volume occupied by the VBL itself is small (where the film thickness is small). This VBL pair 6 can move in the Bloch domain wall by a gyroscopic force generated by a pulse bias magnetic field applied in a direction perpendicular to the film surface of the ferromagnetic film forming the stripe domain.

In the VBL pair stabilization method of the present invention, no processing is performed on the layer holding the VBL pair. The mere presence of the coating layer allows the VBL to interact with the coating layer. In the conventional method, the energy density of VBL is locally changed along the domain wall. In order to provide this change, specifically, ion implantation or the like is used. These methods inevitably cause non-uniformity of properties in the film thickness direction. Therefore, the moving speed of the VBL becomes non-uniform along the film thickness direction, and the VBL may become fragmented.

The present invention can eliminate these drawbacks of the conventional method.

The principle will be explained using FIG. FIG. 2(a) shows a cross section of a part of FIG. 1 cut along a plane including the striped domain domain wall. VBL pair 6 is stabilized in the thin film thickness region. To transfer this VBL pair,
A pulsed bias magnetic field is applied perpendicular to the film surface, and the resulting gyroscopic force is utilized. This section describes how to evaluate the magnitude of gyroscopic force. Figure 2 (b
) qualitatively shows the dependence of the energy shame BL of VBL on the X direction, corresponding to FIG. 2(a). The VBL whose EVBL is stabilized at the lowest point is the EVBL next to it.
Climb over the mountain with the highest value and move to the next valley. Therefore, the gyroscopic force acting on the VBL pair needs to be larger than the maximum value of the gradient of the change in EVBL between the energy trough and peak.

An advantage of the present invention is that it is possible to change the relative difference between the bottom of the potential well at the position where the VBL pair is stabilized and the peak of the so-called bit barrier between the adjacent stable position. It is possible. This is because the ¥IW of the coat layer is different from that of the striped domain holding layer, so there is a large difference in the gyroscopic force that moves one step in the VBL region for a given domain wall driving magnetic field between the striped domain holding layer and the coated layer, and dynamic exchange occurs. Due to the increased force, the VBL pair will avoid that position. After that, when the dynamic drive of the domain wall subsides, the potential well becomes the deepest for the VBL pair again at the thinner position of the coating layer. The VBL pair is stabilized there.

Next, we will discuss how to change the thickness of the coating layer. Second
The broken line in Figure (a) shows the case where the film thickness changing region is made very narrow. Correspondingly, the energy EVB of VBL
The dependence of L on the X direction also changes as shown by the broken line in FIG. 2(b). In this case, the gyroscopic force required to move the VBL pair stabilized at a low energy point to the next valley becomes much larger than in the case of the solid line, and becomes difficult to control in practice. Therefore, the wavy structure shown by the solid line is easy to use in practice.

In this method, the VBL energy change due to the film thickness change is not accompanied by a change in the VBL energy density, so the VBL
Unlike the ion implantation method, the response to the pair of gyro forces does not change discontinuously across the film thickness direction. Therefore, the probability of instability such as VBL being divided at the middle of the film thickness when crossing the inter-bit barrier during transfer can be suppressed to a very low level, and stable VBL pair transfer can be obtained.

The content of the invention will be specifically illustrated below using examples.

(Example 1) A method of manufacturing this wave pattern will be explained using FIG. 4.

Positive photoresist MP130 on the bubble material film 11
0 (Shipley Japan, product name), width 5μm2 period 1
Form a pattern 7 with a film thickness of 0 pm and 1 pm (Figure 4a)
.

After pattern formation, post-bake is performed at 135°C for 1 hour. The pattern will then look like 7゛. If paking is performed above this temperature, the pattern width will fluctuate,
Undesirable. On the other hand, if the temperature is too low, the cross-sectional shape of the pattern will remain rectangular, which is undesirable (see Figure 4b).
). Next, polystyrene having a molecular weight of 17,500 is applied using xylene as a solvent. Using a solution containing 10% by weight of styrene, spin coating was performed at a rotational speed of 3000 rpm.
Thus, a polystyrene coating film 9 of about 3,000 layers is obtained on a flat area. The surface after application had a gentle waveform. The height difference of the waveform shape was approximately 1°311m. There was no deformation of the positive photoresist pattern before and after the coating process (FIG. 4C). Next, ion implantation is performed. The injection condition is thickness 1
．． It was determined that ions would penetrate through a 3 μm organic membrane.

Here, 130KeV/He/4.8X 1015 pieces/
am2.50KeV/He/17 x 1015 pieces 7c
m2. Ion implantation is performed in the portion of the layer coated on the surface of the striped domain holding layer shown at 11' in FIG. 4(d). It is generally known that chemical etching resistance changes when ion implantation is performed on the coating layer material because lattice strain is induced in the implanted layer. After removing the
When immersed in phosphoric acid at 90°C for 10 minutes, the results shown in Figure 4 (e
), the height difference is 0. The coating layer could be processed into a waveform shape of Qm.

The stripe domain-retaining material described above is 5 LPE-grown on a Gd5Ga50.2(111) substrate.
pm bubble material (YSmLuCa)3(FeGe)5o
1□ film (film thickness = 3.88 pm, stripe width = 5.0
pm, 4 nMs = 202 Gauss, (YEuCa) 3 (FeGe) 50 □, which has a smaller damping constant α than the stripe domain holding layer, was grown directly on the liquid phase epitaxial layer. 5p with wavy structure shown in Figure 1
For a sample formed to have m period (mask pattern width 3 pm or 2 pm) and peak height 0° 4 pm, a stripe domain was placed in this region and the stability of the VBL pair was investigated. It was confirmed that it was stabilized in the trough. Furthermore, when a rectangular wave-like pulsed bias magnetic field with a intensity of 10 ns was applied to the stabilized VBL pair, the VBL pair climbed over the peak of the wave-like structure at an amplitude of around 150e.

(Example 2) A coating layer was used instead of Example 1, and the damping constant α was larger than that of the striped domain retention layer (YSmLu
Using the Ca)3(FeGe)5012 epitaxial film, it was confirmed that the VBL pair was stabilized in the troughs of the wavy structure as in Example 1. Furthermore, when a rectangular pulsed bias magnetic field with a width of 10 nsec was applied to the VBL pair stabilized in the valley, the VBL pair climbed over the peak of the wave-like structure at an amplitude of around 25 Oe.

(Effects of the Invention) The present invention improves the stability of Bloch line pairs to the striped domain domain wall and the stability of transfer along the domain wall, which are one of the most important elements in Bloch line memory, compared to conventional methods. I was able to improve it.

[Brief explanation of drawings]

FIG. 1 is an overview diagram of the vertical Bloch line stabilizing and holding means according to the present invention, and FIGS. 2(a) and (b) show the ferromagnetic stripe domain holding layer and the ferromagnetic properties when cut along the plane including the domain walls, respectively. FIG. 3 is a diagram showing the cross section of a body coat layer and the positional dependence of Bloch line energy. FIG. 3 is a configuration diagram of a striped domain retention layer, and FIG. 4 is a diagram showing an example of the process of forming an element. 3...
Stripe domain, 4,4'...Stripe domain domain wall, 5...Magnetization within the stripe domain, 5'.
... Magnetization outside the stripe domain, 6... Vertical Bloch line (VBL) pair, 700. Substrate, 810. Positive type photoresist, 8ζ... Photoresist pattern after post baking, 91.・Polystyrene, 10'...
Susumu Uchihara, a patent attorney who was injected with ions, ``Papa・' $ 2 Figure (a (I))

Claims (1)

[Claims] Ferromagnetic film (
In a magnetic memory element that uses a pair of adjacent perpendicular Bloch lines formed in a Bloch domain wall around a striped domain existing in a ferromagnetic film (including a ferromagnetic film) as a storage information unit, a damping constant is provided on the surface of the ferromagnetic film. A magnetic memory element, characterized in that the magnetic memory element is directly coated with a ferromagnetic film different from the ferromagnetic film, and the thickness of the coating layer varies locally along the Bloch domain wall of the striped domain retention layer.