JPS61204888A - Magnetic storage element - Google Patents

Abstract

PURPOSE:To suppress the instability that a pair of vertical Bloch lines VBL disappear during transfer along a stripe domain magnetic wall by sticking a ferrimagnetic material film, which is opposite to the direction of spontaneous magnetization, to one surface of a ferrimagnetic material. CONSTITUTION:A stripe domain holding ferrimagnetic material layer 2 is stuck on a substrate 1. A ferrimagnetic material layer 3 whose manner of contribution is opposite to that from individual constituting atoms to the direction of spontaneous magnetization of said ferrimagnetic material layer 2 is stuck directly to the layer 2. Thus, the quick increase of an energy density EL of VBL on the surface of the film is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a nonvolatile ultra-high density solid state magnetic memory element.

(Prior art and its problems) Aiming for high-density solid-state magnetic storage elements, magnetic bubble elements have been developed in various places, including permalloy devices, ion-implanted continuous disk devices, current-driven devices, and so-called hybrid devices that combine these devices. There is a lot of activity going on. The limits of densification of these devices are
It has been said that this problem lies in photophosphorographic technology for forming bubble transfer paths. However, the technology has progressed rapidly in recent years. As a result, the issue of materials for increasing density, that is, to what extent the bubble diameter can be reduced, has once again become an issue. With the currently used garnet materials, the minimum attainable bubble diameter is said to be 0.3 μm. Therefore, a bubble material that retains bubbles with a diameter of 0.3 μm or less must be found other than garnet powder.

This is not easy and is even considered to be the limit of bubble density.

Bloch domain walls, which form the boundaries of ultra-high density magnets, can significantly improve the densification limit based on the characteristics of the bubble retention layer and keep the information readout time at the same level as conventional devices. A device has been invented that uses vertical Bloch lines, which are statically and stably present in the device, as a memory unit. (Japanese Patent Application No. 57-182346) One of the most important parts of this device is the information storage section (hereinafter referred to as the minor loop). This magnetic memory element includes an information reading means, an information writing means, and an information storage means, and is present in a ferromagnetic film (including a ferrimagnetic film) whose easy magnetization direction is perpendicular to the film surface. A pair of adjacent vertical Bloch lines (hereinafter referred to as VBL) formed in the Bloch domain wall around the stripe domain is used as a storage unit, and means is provided for transferring the vertical Bloch lines within the Bloch domain wall.

In such a magnetic memory element, it is essential to stably hold the V13L pair of striped domain domain walls written as information and to be able to selectively transfer one bit at a time. As a method of maintaining stability,
-065826, along the Bloch domain wall around the stripe domain that constitutes the minor loop,
Locally changes the direction of magnetic anisotropy within the film plane. In this way, along the stripe I/main domain wall, positions where the VBL pair stably exists and positions where it does not exist can be created.

Regarding the other condition, selective transfer of each bit of the VBL pair, as described in Japanese Patent Application No. 58-065826, a uniform pulse bias magnetic field is applied to the entire region where the stripe domain exists, and the domain walls are It is only possible to move dynamically and use gyroscopic force, which is one of the reactions that occurs in the position of the V-BL pair. Reason 10 for this is that the VBL pair disappears during transfer. VB
L pair disappears. The reason why the VBL structure changes along the thickness direction of the striped domain retention layer is that the striped domain retention layer is a thin film and has an easy magnetization direction in the normal direction to the retention layer film surface. The figure shows the situation. Both sides of the striped domain 4 are surrounded by Bloch domain walls 5 and 5'.

πΔ0 is the width of the domain wall. The outside of the domain wall 5 has magnetization 7 in the opposite direction (downward) to the direction 6 of magnetization M (upward) in the stripe domain. Therefore, on the film surface of the striped domain portion 4 of the striped domain holding layer, a {circle around (2)} magnetic pole is induced on the upper side and an e magnetic pole is induced on the lower side. On the other hand, in the area outside 5 and 5', a magnetic pole ζ is induced on the upper film surface, and a magnetic pole is induced on the lower side. As a result, an in-plane magnetic field H8 is generated in the direction normal to the domain wall near the film surface of the domain walls 5, 5', which have planes parallel to the normal to the film surface. In the case of Figure 5, the direction of H8 is 5, the upper surface of the membrane faces left, the lower surface faces right, and 5I.
In this case, the upper surface of the membrane faces to the right, and the lower surface faces to the left.

Due to the influence of H8, the direction of magnetization on the center line of the domain wall also gradually rotates from the right in 5 along the film thickness direction from the bottom to the top of the film surface, and becomes leftward on the top surface of the film. 5′
Inside, the bottom side faces left, and the top side faces right.

This change in the domain wall structure in the film thickness direction also has a large effect on the VBL characteristics. FIG. 6 shows the state of magnetization rotation of the VBL portion 8 in the bubble domain domain wall with respect to both surfaces of the stripe domain holding layer and the center of the film thickness. The magnetization at the center of this VBL is oriented toward the central axis of the bubble domain along the normal to the surface of the bubble domain domain wall.

In this case, the in-plane magnetic field H3 is directed toward the central axis of the bubble domain on the top surface of the bubble domain, and toward the outside on the bottom surface.The magnetization on the center line of the six domain walls is aligned in the direction of I(s) near the film surface. However, near the center of the film thickness, the contributions from the top and bottom surfaces cancel each other out and become zero, and the magnetization at the center of the domain wall becomes the original direction of magnetization of the Flo/Y-ho domain wall (parallel to the domain wall surface). When the VBL exists in a domain wall with such properties, the magnetization on its center line is oriented in the same direction as the surrounding magnetization on the upper surface of the film, and no energy is stored in the VBL region.On the other hand, on the lower surface, the magnetization of VBL is Since the direction is 180° different from the direction of the surrounding domain wall magnetization, exchange energy is stored in VBL.Therefore, the energy EL (VBLO) changes along the film thickness.

FIG. 7 shows this situation qualitatively.

These are the results of calculating the energy E r- per VBL unit length with respect to the film thickness of the stripe domain holding layer.

Assuming that the left end of the horizontal axis in FIG. 7 is the lower surface of the film and the right end is the upper surface of the film, the film thickness dependence of EL of VBL in FIG. 6 is expressed by 11. The EL is very high on the bottom surface of the membrane. On the other hand,
If the magnetization on the VBL center line is directed outward in the normal direction of the bubble domain domain wall in FIG. 6, the film thickness dependence of EL as shown in FIG. 7 11' is obtained.

This dependence of EL on film thickness is achieved through the following process.
This leads to the disappearance of the VBL pair. FIG. 8 shows the VBL in the Bloch domain wall in the striped domain retention layer. 8,
8' is a VBL structure used as an information carrier in the present invention. 8 corresponds to 11.8' corresponds to 11' in FIG. 8
In the case of VBL 8', the magnetization on the center line is aligned in the same direction along the domain wall surface normal direction throughout the film thickness direction.

On the other hand, the direction of magnetization on the center line of VBL 12 is opposite between the lower side and the upper side with the center of the film thickness as the boundary. In any part, the magnetization coincides with the direction of Ha. At this time, there is a singular point 13 called Bloch point at the center of the film thickness. By entering this point, the change in EL becomes smaller over the film thickness direction. In other words, in Figure 7, E
L changes along 11' in the lower part from the membrane center, and changes along ]1 in the upper half, like 8.8I, ](l
A sudden change in the thickness along the film thickness direction was avoided. However, if Bloch points are included, 1. The polarity of VBL is reversed between the upper and lower halves.

In this Bloch line memory, in order to move VBL, which is an information carrier, along a striped domain domain wall, a gyroscopic force, which is a reaction that occurs when a pulse bias magnetic field is applied to the domain wall and moves it, is used. This gyro force is V
The direction of movement is determined depending on the polarity of BL. therefore,
As shown in Figure 8, 12, VBL shares parts with opposite polarity.
As a result, it cannot be moved by a pulsed bias magnetic field.

When an adjacent VBL collides with this immovable VBL, the portions of the two VBLs having mutually different polarities in the film thickness direction recombine, and the Bloch line as a whole eventually disappears. This is a very big problem for general-purpose devices.

(Object of the Invention) The object of the present invention is to eliminate such conventional drawbacks, to stably maintain the VBL pair of the striped domain domain wall, which is a minor loop, and to enable selective transfer of 1 bit at a time. An object of the present invention is to provide an ultra-high density magnetic memory element that uses VBL pairs as information units.

(Structure of the Invention) The present invention uses, as a memory unit, a VBL pair consisting of two adjacent VBLs formed in a protubular domain wall around a stripe domain existing in a ferrimagnetic film whose easy magnetization direction is perpendicular to the film surface. In a magnetic memory element used as a ferrimagnetic material, a ferrimagnetic film is formed on at least one surface of the ferrimagnetic material, and the ferrimagnetic material film has a contribution that is reversed in the direction of spontaneous magnetization of the ferrimagnetic material compared to the contribution from each constituent atom. This is a magnetic memory element characterized by directly attaching.

(Detailed Description of Configuration) By adopting the above-described configuration, the present invention solves the problem of maintaining stability of the VBL pair in the minor loop of the prior art. The configuration will be explained in detail below.

FIG. 1 is a diagram showing the configuration of a striped domain holding layer in a minor loop portion according to the present invention. A ferrimagnetic layer 2 for holding striped domains is provided on a substrate 1. A ferrimagnetic material layer 3 is directly placed on top of the ferrimagnetic material layer 3, in which the contribution from each constituent atom to the direction of spontaneous magnetization of the ferrimagnetic material is reversed. By doing this, V
It is possible to prevent the energy density EL of BL from rapidly increasing at the film surface. The mechanism will be explained using a general ferrimagnetic garnet film as an example of a material for a striped domain retention layer. In FIG. 3, 8 and 8' are marked with black. V
From the dependence of the energy density EL of BL8 and BL8' on the film thickness direction (FIG. 7), in BL8, F]L is drawn at the bottom end of the film, and in BL8', EL is high near the top surface of the film. A ferrimagnetic material 3 is attached to the upper surface of the striped domain holding layer 2 shown in FIG. 1, in which the manner of contribution from each constituent atom to the direction of spontaneous magnetization of the layer 2 is reversed. In this way, 2.3
Exchange energy is stored at the upper end 9 of VBL 8 at the boundary.

This is because the magnetic domain structure of the ferrimagnetic layer 3 depends on the domain structure of the stripe domain holding layer 2, and the magnetization direction of 3 near the domain wall existing in 2 is the direction of the in-plane magnetic field component Ha generated from the domain structure of 2. directed towards. It is now assumed that the magnetization of layer 2 is oriented in the same direction as the atomic magnetic moment at position 24d, and the magnetization of layer 3 is in the same direction as the atomic magnetic moment at position 16a. The contribution of the atomic magnetic moment of the rare earth ion at the 24C position is the same as the direction of the atomic magnetic moment at the 16a position when the atomic number is 64 or higher, and for convenience below, the contribution of the atomic magnetic moment to the atomic magnetic moment at the 16a position is shown below. Now let us consider the relative magnitude of the atomic magnetic moment at the 16a position and the atomic magnetic moment at the 24d position.

The direction of magnetization per unit cell is determined by comparing the sum of the atomic moments at 168 positions and the sum of the atomic magnetic moments at 24d positions, and matches the larger one.

In other words, the magnetization near the top of VBL points in the H'S direction, which means that the atomic magnetic moment at the 24d position is H
The fact that the magnetization in layer 3 is oriented in the H8 direction means that the atomic magnetic moment at position 16a is aligned in the Ha direction. Considering this, at the boundary 9 between the upper end of VBL 8 and VBL 3, the atomic magnetic moment at position 24d of layer 2 and the atomic magnetic moment at position 168 of layer 3 are in the same direction. In ferrimagnetic garnet, this is the atomic magnetic moment at the 24d position and 1
This contradicts the property that the atomic magnetic moments at the 68th position are coupled antiparallel to each other and stabilized. therefore,
The exchange energy is stored in the part 9.

This exchange energy changes the magnetization direction of the ferrimagnetic layer 3 to H
Either the magnetization can be reversed against a, or the magnetization near the top of VBL8 can be reversed, but in either case, the Bloch point implanted at position 9 can easily reach the center of the film thickness of 2. I can't proceed. In order for the Bloch point to advance to the center of the film thickness of 2, the film thickness of 3 must be increased so that the magnetization of 2 is reversed. E'L at the upper end of the film thickness of the curve needs to be larger than the value at the center of the film thickness.

The point where the EL at the upper end of the film thickness is equal to the EL at the center of the film thickness connects the Bloch point in the opposite direction to the center of the film thickness of 2, and the arrangement satisfies the stable bonding properties unique to ferrimagnetic garnet. There is.

Therefore, no replacement key is stored in the 10th part. Rather, since H8 at the upper end of VBL8' reflecting the magnetic domain structure of 2 directs the magnetization at the 16a position of layer 3 in the same direction as )Is, the magnetization direction near the upper end of VBL 2 is opposite to )is. It will be stabilized. Therefore, in the absence of the film No. 3, the direction of the Ha force was easily reversed, and Bloch point injection at point No. 10, where Bloch point injection was easy, was suppressed.

FIG. 2 shows another example of the present invention, in which the relationship between the lower surface of the striped domain holding layer 2 and the substrate is similar to that of the upper surface, and the contribution from each constituent atom to the direction of spontaneous magnetization of 2 is greater than that of the upper surface. A ferrimagnetic film with reversed direction is attached so as to be in direct contact with 2. By doing so, Bloch point injection from the upper hook surface layer above the striped domain holding layer is suppressed.

FIG. 4 explains the mechanism. At the lower end of VBL8, the same structure as the upper end of VBL8' is realized, and at the lower end of VBL8', the same structure as the upper end of VBL8 appears.

From this, the Bloch line 8 where float points are likely to enter from the lower end of the striped domain holding layer 2 is the layer 3.
' suppresses Bloch point injection from 10'. On the other hand, Bloch line 8 where Bloch points tend to enter from the upper end of striped domain holding layer 2
/ is suppressed from being injected from Bloch point 10 by layer 3.

Examples are shown below.

Example 1 411m bubble material (YSmLuCa)s (FeG
e).

O1□ is used as the material for the striped domain holding layer 2, and EuCa5, which is called a high 2 material, is used as the material for the ferrimagnetic layer 3.
Using iGeYIG, Gd5ca5o11 (,111
) on the substrate (ysmI, uca)3(FeGe)! 10
After liquid phase epitaxial growth of 12, ELICaSI
GeYIG was liquid phase epitaxially grown thereon. By doing this, the VBL written in the bubble domain existing in layer 2 becomes α■ higher than the amplitude of the pulse bias magnetic field at which VBL disappears by 20 times compared to a film without ferrimagnetic layer 3, and layer 3 becomes It has been found to increase the stability of VBL within the domain wall of layer 2.

Example 2. 4pm bubble material (YSmLuCa)s (F
eGe)sO+2 is used as the material of the striped domain holding layer 2, EuCa5iGeYIG called high 2 material is used as the material of the ferrimagnetic layer 3.3', Gd3Ga,
On 0.2 (111) board, Ellcas IGe
YIG was grown by liquid phase epitaxial growth, and (YSm
+LuCa)s(FeGe)! 10□2 was grown by liquid phase epitaxial growth, and then EuCa5+GeYI was grown again on top of it.
G was grown by liquid phase epitaxial growth. By doing this, the VBL written to the bubble domain existing in layer 2 is 3.
, 3I, the amplitude of the pulse bias magnetic field at which VBL disappears is 60% higher than that of the film without layer 3.
was found to increase the stability of VBL within the domain wall of layer 2.

Example 3 1 μm bubble material (YSmLuCaBi)s (Fe
Ge).

01□ was used as the material for the striped domain holding layer 2, and Eu, which is called a high 2 material, was used as the material for the ferrimagnetic layers 3 and 3'.
Using Ca5iGeY'IG, Gd5G%012(11
1) First, EuCa5iGeYIG is grown by liquid phase epitaxial growth on the substrate, and then (YSmLuCaB')3
(FeGe)! 1012 by liquid phase epitaxial growth,
On top of that, EuCa5iGeYIG was again grown by liquid phase epitaxial growth. By doing this, the amplitude of the pulse bias magnetic field at which the VBL disappears is 60% higher than that of the film without 3.31, and the VBL written in the bubble domain existing in layer 2 becomes 60% higher than the film without 3.31. 2I Reason■
It was found to increase the stability of L.

(Effects of the Invention) The present invention makes it possible to suppress the instability that occurs during transfer along the BI#lS stripe domain domain wall, which has been a problem in the past, and makes it possible to reduce the reliability of Bloch line memory. improved.

[Brief explanation of the drawing]

1 and 2 are diagrams showing an example of the structure of the striped domain holding layer of the present invention, FIG. 3 is a diagram illustrating the basic principle used in the present invention, and FIG. 4 is a diagram illustrating another basic principle. Figure 5 is an explanatory diagram of the dependence of the magnetization direction on the domain wall center line on both sides of the stripe domain in the film thickness direction, and Figure 6 is an illustration of the VB in the domain wall of the baffle domain.
Figure 7 shows the magnetization rotation in the L section, Figure 7 shows the dependence of the energy density EL per VBL unit length in the film thickness direction, and Figure 8 shows the various types of V existing in the striped domain domain wall.
An explanatory diagram of BL. In the figure, 1: substrate, 2 varnish drive domain holding layer, 3: ferrimagnetic layer, 4 varnish drive domain 5.5
' Varnish drive domain domain wall, 6. Magnetization within the strive domain, 7. Magnetization outside the strive domain. 8.8'
:VBL, 9.10: Boundary between the upper end of VBL and the coating layer,
11.11': Curve showing the dependence of VBL energy density on the inner film thickness of the stripe domain retention layer 12: VBLo13 with Bloch point: Bloch point.

Claims (2)

[Claims] (1) Neighboring magnetic fields created in Bloch domain walls around striped domains existing in a ferrimagnetic film that includes an information reading means, an information writing means, and an information storage means, and whose easy magnetization direction is perpendicular to the film surface. In a magnetic memory element that uses a pair of perpendicular Bloch lines as a storage information unit, at least one surface of the ferrimagnetic material has a structure in which the contribution of each constituent atom to the direction of spontaneous magnetization of the ferrimagnetic material is different from that of each constituent atom. A magnetic memory element characterized by directly attaching a reversed ferrimagnetic film. (2) On both the upper and lower surfaces of the ferrimagnetic film holding the striped domains, the contribution from each constituent atom to the direction of spontaneous magnetization of the ferrimagnetic material is reversed. A magnetic memory element according to claim 1, characterized in that a ferrimagnetic film is directly attached thereto.