JP2612560B2 - Bloch line memory - Google Patents

Description

The present invention relates to a Bloch line memory. The Bloch line memory can be applied to various electronic devices as a memory capable of recording information at an extremely high density.

2. Description of the Related Art At present, various types of memories such as a computer external memory, an electronic file memory, and a still image file memory include various types such as a magnetic tape, a Winchester disk, a floppy disk, an optical disk, a magneto-optical disk, and a magnetic bubble memory. A memory device is being used. Of these memory devices, other memories except the magnetic bubble memory require that the recording / reproducing head be moved relatively to the memory when recording or reproducing information. That is, with such a relative movement of the head, the head records an information sequence fixedly on the information track or reproduces the information sequence fixedly recorded on the information track.

However, in recent years, as the recording density is increasingly required to be higher, the tracking control for causing the head to accurately follow the information track becomes complicated, and the quality of the recording / reproducing signal deteriorates due to insufficient control. In addition, the quality of the recording / reproducing signal is degraded due to vibration of the head moving mechanism or dust adhering to the memory surface. In the case of a memory that performs recording and reproduction in a non-contact manner with a head such as an optical disk, focusing control for focusing is required, and the control is insufficient, so that the quality of a recording / reproduction signal is deteriorated. Has occurred.

On the other hand, the magnetic bubble memory can record information at a predetermined position and transfer the recorded information, and can reproduce the information at a predetermined position while transferring the information. It is considered that relative movement is not required, and therefore, even when the recording density is increased, the above-described problem does not occur and high reliability can be realized.

However, magnetic bubble memories use circular magnetic domains (bubbles) generated by applying a magnetic field to a magnetic thin film having an easy axis of magnetization in a direction perpendicular to the film surface such as a magnetic garnet film as information bits. The smallest bubble (0.3 μm in diameter) limited by the material properties of the garnet film
Even if m) is used, the recording density is limited to several tens of Mbits / cm ² , and it is difficult to further increase the recording density.

Therefore, recently, a Bloch line memory has been attracting attention as a memory having a recording density exceeding the recording density limit of the magnetic bubble memory. This Bloch line memory uses a pair of Nehru domain wall structures (Bloch lines) sandwiched by Bloch domain wall structures existing around magnetic domains generated in a magnetic thin film as information bits.
It is possible to increase the recording density by nearly two orders of magnitude compared to the magnetic bubble memory. For example, when a garnet film having a bubble diameter of 0.5 μm is used, it is possible to achieve a recording density of 1.6 Gbit / cm ² [“Nikkei Electronics” 19
August 15, 1983, p. 141-167].

FIG. 4 is a schematic perspective view of an example of a magnetic body structure constituting the Bloch line memory.

In the figure, reference numeral 2 denotes a substrate made of a non-magnetic garnet such as GGG, NdGG, etc., on which a magnetic garnet thin film 4 is provided. The film can be formed by, for example, a liquid phase epitaxial growth method (LPE method), and its thickness is, for example, about 5 μm. Numeral 6 denotes a stripe-shaped magnetic domain formed in the magnetic garnet thin film 4, and a domain wall 8 is formed as a boundary region inside and outside the magnetic domain. The width of the stripe-shaped magnetic domain 6 is, for example, about 5 μm, and the length is, for example, about 100 μm. The thickness of the domain wall 8 is, for example, about 0.5 μm. As indicated by the arrows, the magnetic domains 6
Inside, the direction of magnetization is upward, while outside the magnetic domain 6, the direction of magnetization is downward.

The direction of magnetization in the domain wall 8 is rotated so as to be gradually twisted from the inner surface (that is, the surface on the magnetic domain 6 side) to the outer surface. The direction of this rotation is reversed on both sides of the Bloch line 10 that exists in the domain wall 6 in the vertical direction. In FIG. 4, the direction of magnetization at the center of the domain wall 8 in the thickness direction is indicated by an arrow, and the direction of magnetization in the Bloch line 10 is also indicated.

Incidentally, a downward bias magnetic field H _B is applied from the outside to the aforementioned such magnetic structures.

As shown, there are two types of Bloch lines 10 having different directions of magnetization, and the presence or absence of a pair of these Bloch lines is associated with information “1” and “0”. The Bloch line pairs are located at regular positions in the domain wall 8, that is, at any one of potential wells. Each of the Bloch line pairs is sequentially transferred to an adjacent potential well by applying a pulse magnetic field perpendicular to the substrate surface. Thus, the recording of information in the Bloch line memory (writing of the Bloch line pair to the domain wall 8) and the reproduction of the information recorded in the Bloch line memory (reading of the Bloch line pair in the domain wall 8) are performed by the Bloch line pair. Is transferred at a predetermined position while being transferred within the domain wall 8. Both recording and reproduction of the above information can be performed by applying a pulse magnetic field of a predetermined intensity perpendicular to the substrate surface to a predetermined portion, respectively. Although not shown in FIG. As a pulse magnetic field applying means for reproduction, a conductor pattern for applying a pulse is formed on the surface of the magnetic thin film 4 with a predetermined positional relationship with respect to the stripe-shaped magnetic domains 6.

[Problems to be Solved by the Invention] In the Bloch line memory as described above, formation of a potential well for a Bloch line pair is performed, for example, by giving a regular pattern to the surface of the magnetic thin film so as to cross the domain wall. It is done by doing.

FIG. 5 is a partial plan view of a Bloch line memory showing an example of such a pattern.

In the figure, stripe magnetic domains 6 are provided on the surface of the magnetic thin film 4.
A large number of line-shaped patterns 9 extending in the direction crossing are provided in parallel. The pattern is, for example, Cr, Al, A
It is made of a conductor layer of u, Ti or the like, has a width of, for example, about 0.5 μm, and has an arrangement pitch of, for example, about 1 μm. The arrangement of the potential wells in the domain wall 8 can be made regular and periodic due to the strain based on the formation of the patterned conductor layer. Also, as the pattern 9,
In addition to the conductor layer, for example, a magnetic layer, and further, H ions,
It is also possible to use those in which ions such as He ions and Ne ions are implanted in the above-described pattern near the surface of the magnetic thin film 4. Each potential well formed by these patterns is symmetric with respect to the Bloch line transfer direction.

By the way, as described above, the transfer of the Bloch line is performed by applying a pulse magnetic field perpendicular to the film surface of the magnetic thin film 4,
This is performed by moving to the adjacent potential well by utilizing the precession of the magnetization generated by this. However, in the case of a symmetric potential well as described above, a simple rectangular pulse magnetic field cannot be used for stable movement in a specific direction using a pulse magnetic field. For this reason, as shown in FIG. 6, a pulse magnetic field having a shape whose fall time is sufficiently longer than the rise time is used as the pulse magnetic field Hp for Bloch line transfer, whereby irreversible transfer in a specific direction is performed. Was surely done.

For this reason, the electric circuit for generating the pulse magnetic field is more complicated than in the case of generating a rectangular pulse magnetic field, and the fall time is longer, so that it is difficult to improve the transfer speed and the power consumption is further increased. There was a point.

Accordingly, an object of the present invention is to solve the above-described problems of the conventional Bloch line memory and to provide a Bloch line memory capable of realizing stable, high-speed and good Bloch line transfer with a simple configuration. .

[Means for Solving the Problems] According to the present invention, there is provided a Bloch line memory for recording information using a Bloch line in a domain wall of a magnetic domain in a magnetic thin film. A potential well in which the Bloch line is more likely to move in a predetermined direction than a reverse direction is periodically formed along the domain wall, and the Bloch line is transferred in the predetermined direction along the domain wall. Memory is provided.

EXAMPLES Hereinafter, specific examples of the present invention will be described with reference to the drawings.

FIG. 1 (a) is a partial plan view of a Bloch line memory according to the present invention, and FIGS. 1 (b) and 1 (c) are a BB sectional view and a CC sectional view, respectively.

In FIG. 1, 2 is a non-magnetic garnet substrate,
4 is a magnetic garnet thin film. In the magnetic garnet thin film, a magnetic domain 6 having a stripe-like planar shape is formed. Reference numeral 8 denotes a domain wall around the stripe magnetic domain 6.

The direction of magnetization in the stripe magnetic domain 6 is upward, and the direction of magnetization in the portion of the magnetic thin film 4 outside the magnetic domain is downward. A downward bias magnetic field is applied from the outside.

In the vicinity of the surface of the magnetic thin film 4, sawtooth ion implantation regions 4 a and 4 b are formed at predetermined intervals so as to cross the domain wall 8. As shown in FIGS. 1 (b) and 1 (c), each ion implantation region 4a, 4b has a depth distribution which continuously changes with respect to the direction of the domain wall 8 (that is, BB direction, CC direction). Have. As shown, the direction of this change is opposite in the ion implantation regions 4a and 4b. The ions to be implanted are preferably ions having a relatively small ionic radius, such as H ions, He ions, and Ne ions. These ions are implanted at about several KeV to several tens KeV, and a maximum depth near the surface of the magnetic thin film 4 The ion implantation regions 4a and 4b of about 3 μm are formed. The shape of the ion implantation regions 4a and 4b can be made into a desired shape by using an appropriate mask at the time of implantation,
For example, the width is about 2 μm and the arrangement pitch is about 4 μm.
Further, the depth of the ion implantation can be controlled by a method in which the ions are narrowed down in a beam shape and the implantation energy is changed, and the position is gradually shifted to scan.

FIG. 2 is a diagram for explaining magnetic properties in the domain wall in the present embodiment.

FIG. 2 (a) is a view similar to FIG. 1 (b), and FIG. 2 (b) shows the magnetic anisotropy at the position in the domain wall corresponding to FIG. 2 (a). FIG. 2 (c) is a graph showing a case where a vertical pulse magnetic field is applied.
FIG. 6 is a diagram showing a moving speed of a Bloch line at a position in a domain wall corresponding to FIG.

As shown in FIG. 2 (b), the magnetic properties change in the ion implantation region 4a and in the vicinity thereof in accordance with the ion implantation depth. In the vicinity of the ion-implanted edge portion of the ion-implanted region 4a (12 in FIG. 2B).
), The direction along the edge side surface, that is, the direction perpendicular to the domain wall 8 becomes the easy axis of magnetization due to the symmetry of the lattice distortion. For this reason, the Bloch line can be stably positioned here, that is, this becomes a directional potential well.

By the way, when the pulse magnetic field Hp is applied in a direction perpendicular to the film surface of the magnetic thin film 4, the moving speed of the Bloch line is It is expressed as Here, γ is a gyro constant, A is an exchange interaction constant, and Ms is a saturation magnetization. It is known that A is significantly reduced by the above-described ion implantation. When the average value of the moving speed of the Bloch line in the film thickness direction is calculated from the above equation, the result is as shown in FIG. 2 (c). This means that the mobility of the Bloch line is asymmetric, and that the mobility in the direction of arrow X in the figure is better than the mobility in the opposite direction.

Therefore, the third vertical pulse magnetic field of substantially rectangular, such as shown in FIG Hp (e.g., rise time t _r = 100 nsec, peak time
Even when t _p = 200 nsec and fall time t _f = 100 nsec), the Bloch line moves in the direction of arrow X and moves to the next stable position by appropriately setting the magnitude of the pulse magnetic field. Does not return to the previous stable position in the opposite direction simultaneously with the disappearance of the pulse magnetic field.

As shown in FIG. 1, since the directionality is opposite between the ion implantation regions 4a and 4b, the same vertical pulse magnetic field is applied to the loop-shaped domain wall 8 in the direction of the arrow X in FIG. 1 (a). The Bloch line moves along.

In the above embodiment, the ion implantation region, which is a different magnetic region, is given directionality by the ion implantation depth distribution. In the present invention, the directionality of the ion implantation region is given by the implantation ion concentration distribution and the implantation ion species. It may be provided by distribution or the like.

[Effects of the Invention] According to the present invention as described above, the Bloch line can be reliably transferred in a specific direction by applying a simple rectangular pulse magnetic field, so that the electric circuit can be simplified and the fall time can be further reduced. , The transfer speed can be improved, the access time can be reduced, the power consumption can be reduced, and a Bloch line memory that can operate stably, at high speed, and satisfactorily with a simple configuration can be realized.

[Brief description of the drawings]

FIG. 1 (a) is a partial plan view of the Bloch line memory of the present invention, and FIGS. 1 (b) and 1 (c) are a BB sectional view and a CC sectional view, respectively. FIG. 2 is a diagram for explaining magnetic properties in the domain wall. FIG. 3 is a diagram showing a waveform of a pulse magnetic field. FIG. 4 is a schematic perspective view of a magnetic structure constituting a Bloch line memory. FIG. 5 is a partial plan view of the Bloch line memory. FIG. 6 is a diagram showing a waveform of a pulse magnetic field. 2: substrate, 4: magnetic thin film, 4a, 4b: ion implantation area, 6: magnetic domain, 8: domain wall, 10: Bloch line.

Claims (4)

(57) [Claims] 1. A Bloch line memory for recording information using a Bloch line in a domain wall of a magnetic domain in a magnetic thin film, wherein a potential well along which the Bloch line is more easily moved in a predetermined direction than in a reverse direction is formed along the domain wall. A Bloch line memory formed periodically and transferring the Bloch line in the predetermined direction along the domain wall. 2. The Bloch line memory according to claim 1, wherein said potential well is formed by implanting ions into said magnetic thin film. 3. A potential well in which the Bloch line is more easily moved in the predetermined direction than in the opposite direction by changing the implantation depth of the ions along the domain wall in a region corresponding to each of the potential wells. A Bloch line memory according to claim 2, wherein: 4. A potential well in which the Bloch line is more easily moved in the predetermined direction than in the opposite direction by changing the ion implantation concentration along the domain wall in a region corresponding to each of the potential wells. The Bloch line memory according to claim 2.