JPH071634B2 - Magnetic memory element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a nonvolatile ultra-high density solid-state magnetic memory element.

(Prior Art) A magnetic bubble element has been conventionally developed as a target for a high-density solid magnetic memory element. However, with the garnet materials currently used, the smallest bubble diameter that can be reached is
It is said to be 0.3 μm. Therefore, a bubble material that holds bubbles having a diameter of 0.3 μm or less must be determined in addition to the garnet material. This is not easy and is even thought to be the limit of bubble densification.

As a super-high density solid magnetic memory element capable of significantly improving the densification limit based on such characteristics of the valve holding layer and keeping the information read time at the same level as the conventional element, A Bloch line pair consisting of two vertical Bloch lines that are statically and stably present in the Bloch domain wall that forms the boundary of the stripe domain formed in the ferromagnetic (including ferrimagnetic) film with the easy magnetization direction. Hereinafter, an element using a VBL pair) as a memory unit was invented (Japanese Patent Application No. 57-182346).

One of the most important parts of this device is VBL
Stabilized in the stripe domain domain wall in the form of a pair, and
The VBL pair is transferred within the Bloch domain wall as needed.

Regarding the VBL vs. stable retention method, Japanese Patent Application No. 8065826 discloses that stripe domain is locally changed along the Bloch domain wall around the stripe domain forming the minor loop by changing the direction of magnetic anisotropy in the film plane. It has been shown that along the domain wall VBL pairs can be engineered into stable and non-stable positions.

(Problems to be solved by the invention) The specific method for locally changing the direction of the magnetic anisotropy in the film plane described in Japanese Patent Application No. 58-065826 is 1) Selective ions to the film. Use the inverse magnetostriction effect based on the lattice strain due to implantation, or 2) use a material with high internal stress to form a pattern on the surface of the stripe domain retention film, give a stress distribution to the film, and use the inverse magnetostriction effect based on it IEEE Transaction on Magnetics Vol, MAG-2
0, No. 5pp 1135-1137 (1984). In 1), the direction of the in-plane magnetic anisotropy is controlled only in the film surface layer portion. This local change of in-plane magnetic anisotropy is a method of controlling only the difficulty of the VBL pair without changing the moving velocity of the domain wall. Therefore, there is no problem if the in-plane magnetic anisotropy is uniformly controlled in the film thickness direction, but only a part of the in-plane magnetic anisotropy is changed, and the surface layer is not ion-implanted. When the boundary with the layer is clear, the gyroscopic force generated for a given domain wall motion velocity is constant, so VV inevitably depends on the difficulty of movement of the VBL pair.
The movement of the BL pair becomes nonuniform along the film thickness direction. As a result, in some cases, VBL may be divided in the middle part of the film thickness, and VBL pairs may disappear. This is a big problem in terms of device reliability. To remove this obstacle, it is desirable to implant ions uniformly in the film thickness direction. However, the essential characteristics of the ion implantation method or the performance of the ion implanter It is quite difficult because Method 2) is 1)
Compared to method (1), the change in the in-plane magnetic anisotropy in the film thickness direction is gentler, and the probability of destabilization during VBL pair movement is smaller than in (1), but there is a tendency for ion implantation to occur. Is the same.

The purpose of the present invention is to eliminate the above-mentioned conventional problems in VBL.
An object of the present invention is to provide an ultrahigh density recording element having a stripe domain domain wall subjected to the anti-stable method.

(Means for Solving the Problem) That is, the present invention has a ferromagnetic material (ferrimagnetic material) having an information reading means, an information writing means, and an information storage means, and having a direction perpendicular to the film surface as an easy magnetization direction. A vertical Bloch line pair composed of two adjacent vertical Bloch lines formed in a Bloch domain wall at the boundary of a stripe domain existing in a film including a film is used as a memory information unit, and
In an element having a means for transferring the pair of vertical Bloch lines in the Bloch domain wall, another type of ferromagnetic film (including a ferrimagnetic film) is directly attached to the surface of the stripe domain holding layer, and along the stripe domain domain wall. A magnetic memory element characterized in that the two film thicknesses are locally changed is presented.

(Operation) The present invention has shown that, by adopting the above-mentioned configuration, the VBL pair, which is an information unit, can be stably held and transferred along the stripe domain domain wall. Hereinafter, the principle of the present invention will be described in detail. As shown in FIG. 3, the surface of the stripe domain holding layer 1 is coated with a ferromagnetic film 2 having a damping constant different from that of the ferromagnetic material. The damping constant of a ferromagnetic substance is, for example, as described on page 94 of Magnetic Engineering Course 4, “Magnetic Bubble” (Maruzen, October 1972) by Shuichi Iida et al. It is a value obtained from the half-width and the resonance frequency, and is a quantity related to the damping effect on the motion of the magnetization in the ferromagnetic material. As shown on page 57 of Magnetic Engineering Course 4, “Magnetic Bubble” (Maruzen, October 1972) by Shuichi Iida et al., The damping constant and the domain wall mobility are in inverse proportion to each other. If the damping constants of the magnetic materials are different, the domain wall mobility μw
Is different. Therefore, when a domain wall is moved by applying a pulse bias magnetic field, the gyroscopic force acting on VBL in the domain wall is different between the stripe domain retention layer and the coat layer.
Exchange interaction energy is stored at the boundary between the stripe domain holding layer and the coat layer. Therefore, VBL tries to avoid that situation. Therefore, if the film thickness of the coat layer is locally changed along the stripe domain wall, VB
The L pair is stabilized where the coat layer thickness is small. FIG. 1 shows how to change the film thickness in the stripe domain domain wall portion according to the present invention. The VBL pairs 6 in the domain walls (Bloch domain walls) on both sides of the stripe domain 3 are stabilized in the portion where the film thickness is thin. This is because the VBL has a higher energy density than the surrounding Bloch domain walls, and is therefore easily stabilized in a place where the occupied volume of the VBL itself is small (where the film thickness is small). The VBL pair 6 is generated in the Bloch domain wall by the gyroscopic force generated by the pulse bias magnetic field applied in the direction perpendicular to the film surface of the pulse via magnetic field applied in the direction perpendicular to the film surface of the ferromagnetic film forming the stripe domain. Can be moved.

In the VBL pair stabilization method of the present invention, nothing is processed on the layer holding the VBL pair. The presence of the coat layer gives the VBL interaction with the coat layer. In the conventional method, the energy density of VBL is locally changed along the domain wall. To give this change, specifically, ion implantation or the like is used. These methods inevitably cause non-uniformity of characteristics in the film thickness direction. Therefore, the moving speed of the VBL becomes non-uniform along the film thickness direction, and the VBL is divided. In the present invention, such drawbacks of the conventional method can be eliminated.

The principle will be described with reference to FIG. FIG. 2 (a) shows a cross section obtained by cutting a part of FIG. 1 with a plane including the stripe domain domain walls. VBL vs. 6 The film thickness is stabilized in a thin region. To transfer this VBL pair, a pulse bias magnetic field is applied in the direction perpendicular to the film surface, and the gyro force generated thereby is used. We will describe how to evaluate the magnitude of gyro force. VB is shown in Fig. 2 (b).
The x-direction dependence of the energy E _VBL of L is qualitatively shown corresponding to FIG. A _VBL whose E _VBL is stabilized at the lowest position moves over to the valley next to it, overcoming the next highest E _VBL peak. Therefore, the gyro force acting on the VBL pair needs to be larger than the maximum value of the gradient of the change in _EVBL between the valley and the peak of energy.

The advantage of the present invention is that when the VBL pair is driven, 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 so-called bit barrier peak term between the adjacent stable positions. It is possible. This is because the μw of the coating layer is different from that of the stripe domain holding layer, so that there is a large difference between the stripe domain holding layer and the coating layer in the gyroscopic force that acts on the VBL portion with respect to the applied domain wall driving magnetic field, and dynamic exchange force is obtained. As it grows, the VBL pair will avoid that position. After that, when the dynamic drive of the domain wall subsides, the potential well becomes deepest again for the VBL pair at the thin position of the coat layer. The VBL pair is stabilized there.

Next, how to change the film thickness of the coat layer will be described. Second
The broken line in FIG. 7A shows the case where the film thickness change region is extremely narrowed. Corresponding to this, VBL energy E _VBL x
The direction dependence also changes as shown by the broken line in FIG. In this case, the energy was stabilized at a low place.
The gyro force required to move the VBL pair to the next valley is much larger than that for the solid line, and is actually difficult to control. Therefore, the corrugated structure shown by the solid line is practically easy to use.

With this method, the change in VBL energy due to the change in film thickness
Since there is no change in the energy density of the VBL, the response of the VBL pair to the gyro does not change discontinuously along the film thickness direction as in the ion implantation method. Therefore, the probability of instability such as VBL being divided at the middle part of the film thickness when overcoming the bit-to-bit barrier during transfer can be suppressed to a very low level, and stable VBL pair transfer can be obtained.

The contents of the invention will be specifically described below with reference to examples.

Example 1 A method of manufacturing this wave pattern will be described with reference to FIG.

A pattern 8 having a width of 5 μm, a period of 10 μm and a film thickness of 1 μm is formed on the bubble material film 2 with a positive photoresist MP1300 (trade name of Shipley Japan Co., Ltd.) (FIG. 4A). After pattern formation, post bake is performed at 135 ° C. for 1 hour. Then the pattern looks like 8 '. If baking is performed at a temperature higher than this temperature, the pattern width changes, which is not preferable.
Conversely, if the temperature is too low, the cross-sectional shape of the pattern remains rectangular, which is not preferable (FIG. 4B). Then the molecular weight
17500 polystyrene is applied with xylene as solvent. Using a solution in which 10 weight percent of styrene is dissolved,
At a spin coating rotation speed of 3000 rpm, a polystyrene coating film 9 having a flat area of about 3000 Å is obtained. The surface after application had a gentle waveform. The difference in height of the waveform was about 13 μm.
There was no deformation of the positive photoresist pattern before and after the coating process (Fig. 4c). Next, ion implantation is performed. The implantation conditions were set so that the ions would penetrate through a 1.3 μm thick organic film.

Here, 130 KeV / He / 4.8 × 10 ¹⁵ pieces / cm ² , 50 KeV / He / 1.7 × 10
^{It was set to 15} pieces / cm ² . Ions are implanted into the portion of the layer coated on the surface of the stripe domain holding layer shown by 10 'in FIG. 4 (d). It is known that when ion-implantation is performed on the coating layer material, lattice strain is induced in the implantation layer, and thus the chemical etching resistance is generally changed. Fig. 4 (e) when the sample was immersed in phosphoric acid at 90 ° C for 10 minutes after removing
As shown in Fig. 3, the coat layer could be processed into a corrugated shape with a height difference of 0.4 µm.

The stripe domain holding material is Gd ₃ Ga ₅ O ₁₂ (111)
5μm bubble material (YSmLuCa) ₃ (Fe
Ge) ₅ O ₁₂ film (thickness = 3.88 μm, stripe width = 5.0 μ
m, 4πMs = 202Gauss on top of which the damping constant q is smaller than that of the stripe domain retention layer directly (YEuCa) ₃
Liquid phase epitaxial growth of (FeGe) ₅ O ₁₂ was performed. The wave-like structure shown in FIG. 1 has a period of 5 μm (mask pattern width 3 μm
m or 2 μm), a sample formed to have a peak height of 0.4 μm was arranged with a strap domain in this region, and the stability of the VBL pair was investigated. The VBL pair was stabilized at the valley of the corrugated structure. Was confirmed. In addition, when a rectangular pulse-shaped pulse bias magnetic field with a width of 10 ns was applied to the stabilized VBL pair, the VBL pair climbed over the peaks of the wavy structure around an amplitude of 150e.

(Example 2) As a coating layer instead of Example 1, the damping constant α is larger than that of the stripe domain retention layer (YSmLuCa).
It was confirmed that the VBL pair was stabilized in the valley portion of the corrugated structure using the ₃ (FeGe) ₅ O ₁₂ epitaxial film as in Example 1. Also, the width of the VBL pair that is stabilized in the valley is 1
When a rectangular pulse bias magnetic field of 0 nsec was applied, the VBL pair climbed over the ridges of the wavy structure around an amplitude of 250e.

(Effects of the Invention) According to the present invention, stabilization of Bloch line pairs on a stripe domain domain wall, which is one of the most important elements in a Bloch line memory, and stability of transfer along the domain wall, compared to conventional methods. I was able to improve.

[Brief description of drawings]

FIG. 1 is a schematic view of a stabilizing means for holding a vertical Bloch line according to the present invention, and FIGS. 2 (a) and 2 (b) are respectively a ferromagnetic stripe domain holding layer and a ferromagnetic material when cut along a plane including a domain wall. It is a figure which shows the cross section of a body coat layer, and the position dependence of Bloch line energy. FIG. 3 is a configuration diagram of a stripe domain holding layer, and FIG. 4 is a diagram showing an embodiment of a process of forming an element. In the figure, 1 ... Stripe domain holding layer, 2 ... Ferromagnetic material coating layer, 3 ... … Striped domain, 4,4 ′ …… Striped domain domain wall, 5
...... Magnetization in stripe domain, 5 '…… Magnetization outside stripe domain, 6 …… Vertical Bloch line (VB
L) Pair, 7 ... Substrate, 8 ... Positive photoresist,
8 '... photoresist pattern after post-baking, 9
...... Polystyrene, 10 '…… Ion-implanted ferrimagnetic coating layer.

Claims (1)

[Claims] 1. A stripe domain peripheral to a ferromagnetic film (including a ferrimagnetic film) having an information reading unit, an information writing unit, and an information storage unit and having a direction perpendicular to the film surface as an easy magnetization direction. In a magnetic memory element using adjacent vertical Bloch line pairs formed in Bloch domain walls as a memory information unit, a ferromagnetic film having a damping constant different from that of the ferromagnetic film is directly coated on the surface of the ferromagnetic film. Then
In addition, the magnetic storage element is characterized in that the film thickness of the coat layer locally changes along the Bloch domain wall of the stripe domain holding layer.