JPH0363992A - Magnetic memory element - Google Patents

Abstract

PURPOSE:To stably extend only a part near the tip bit position of a stripe domain when information are written and read by setting the width of a groove in the range from 1.0-2 times to double natural width of the stripe domain in a stripe domain holding layer. CONSTITUTION:A groove 4 is provided in an area, where the domain is desired to be held, on the stripe domain holding layer 1 and an auxiliary groove 6 is formed with the separated area between along the groove 4. In the both end parts of the groove 4, a domain generator and means 7 and 8 for local in-phase magnetic field generation are arranged and further, by making groove digging part 10 for stripe domain guide, the stripe domain can be extended to a gate part 11 with high reliability at the time of writing and reading operation. The width (d) of the groove 4 is made larger in comparison of the natural width W0 of the stripe domain 13. Thus, when the information are written and read, only the part near the tip bit position of the stripe domain can be stably extended.

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) This magnetic memory element includes an information reading means, an information writing means, and an information storage means, and has a stripe existing in a ferromagnetic material (including ferrimagnetic material) film whose easy magnetization direction is perpendicular to the film surface. It has means for holding and transferring adjacent vertical Bloch lines (hereinafter referred to as VBL) formed in the Bloch domain wall around the domain as a pair within the Bloch domain wall. For example, when the element configuration is a Major-minal loop configuration, in the Major line, bubbles are used as information carriers, the minor loop is configured with striped domains, and VBL pairs existing in the Bloch domain wall around the bubbles are used as information carriers. To show the overall flow of information, first, information written by the bubble generator (the presence or absence of bubbles) moves along the write major line. In order to sequentially store information for each page in the minor loop, the minor loop is constructed with a Bloch domain wall that can hold VBL pairs so that major line information indicated by the presence or absence of bubbles can be transferred to the minor loop in the form of VBL pairs. It is characterized by its structure, and is an important key to dramatically improving storage capacity. The information (VBL pair) transferred to the minor loop by the write transfer gate can move the striped domain domain wall that constitutes the minor loop. Reading from the minor lube and transferring information to the major line involves converting VBL pairs to bubbles. The bubble detector reads the converted bubble presence/absence column. In this way, by constructing the minor loop with striped domains existing in the bubble material and using VBL pairs instead of bubbles as information carriers on the minor loop, it is possible to achieve a storage density of about two orders of magnitude compared to the bubble element. Improvement can be distantly related.

In this element, an important technique is to arrange a large number of magnetic domains with good stability. One way to deal with this is to move the stripe domain domain wall to the outside of the trench boundary boundary layer thickness step. (Special application Showa 6O-0
79658). The reason for this is that when a stripe domain is set to include the trench and the outside of its boundary, the film thickness step at the trench boundary creates a demagnetizing field that prevents the domain wall outside the boundary from approaching the film thickness step. arise. On the other hand, when the stripe domains are confined within the grooved portion, the difference in film thickness generates a demagnetizing field that strongly suppresses the stripe domains from moving outside the grooved boundary. Therefore, in order to generate a demagnetizing field that prevents the domain wall from approaching the groove boundary step, the stripe domain should be initially set so that the stripe domain domain wall is outside the groove boundary layer thickness step. Must be set.

FIG. 6(a) shows a plan view of the structure, and FIG. 6(b) shows a sectional view. An example of a forming technique for hollowing out the center 4 of a region in the domain holding layer 1 where a domain is desired and arranging a closed domain domain wall to surround it is described in the International Society of Applied Magnetics (Intermag) in April 1986.
In the figure, 2 is the substrate, 3 is the spacer, and 5 is the cutout edge. However, experiments have shown that this method does not work well in areas where the grooves are lined up in parallel. There is a considerable difference in the magnitude of the bias magnetic field that changes the bubble domain into a stripe domain between the region without the trench and the region with the trench, and the disadvantage is that the domain does not extend unless the bias magnetic field is lower than that in the region with the trench. It was found that when the bias magnetic field is lowered until the domain extends in the region between the grooves in the region including the grooved portions, it extends in one of the grooved portions and generates the bubble generator 16. As soon as it appears on the opposite side to the side where the conductor pattern 17 for domain coupling is located, the domain expands and a lotus-shaped domain is formed over the entire area where the conductor pattern 17 is located.For this reason, the domain that has just been extended The domains that have extended through the grooved region with a delay from the above are obstructed by the stray domain and cannot extend to the point where they cross under the conductor pattern 17 for domain junction. After stabilization, the bias magnetic field 9 is applied from the outside to the domain tip for stabilizing the domain.
There was a high probability that it would start to stretch arbitrarily due to fluctuations in the temperature or changes in the temperature of the chip.

In order to eliminate these drawbacks and simplify the application conditions of the external magnetic field for stably arranging the striped domains, as shown in Figure 1(a), the striped domains are spread over the region where it is desired to be stabilized. In this method, a groove (first groove) 4 is created by selectively scraping the retaining layer, and a domain domain wall is stabilized around the groove with the groove as the center. An auxiliary groove (second groove) 6 was provided, and a domain generator 7 and a local magnetic field applying means 8 were provided at both ends of the groove for stabilizing the striped domains, thereby facilitating the formation of the desired domains. By creating the grooved part for stabilizing the stripe domain, the potential well for the domain extending out of the grooved part for stabilizing the stripe domain is prevented from becoming suddenly deeper.
It is now possible to extend the stripe domain with good stability to a predetermined position along the longitudinal direction of the desired groove digging length. Another problem is how to choose the relationship between the width of the stripe domain and the width of the groove.

(Problems to be Solved by the Invention) Conventionally, in order to increase the stripe domain arrangement density, the stripe domain width is a natural width W. The width d of the groove 4 should be
was selected to satisfy d<W. However, under these conditions, the shape of the tip of the stripe domain changed sensitively depending on the static bias magnetic field HB applied from the outside in the direction perpendicular to the film surface for stabilizing the stripe domain. When HB becomes lower than a predetermined value, the tip of the domain 13 swells like the tip of a dogbone, as shown in FIG.

With such a shape of the domain domain wall 14, when the VBL pair is transferred at the stripe domain tip 15, the so-called effective drive magnetic field that is obtained by correcting the drive magnetic field applied from the outside by the demagnetizing field from the boundary 5 of the groove 4 is applied to the domain. The values of the bit position at the tip and the adjacent bit positions on both sides are greatly different from each other and compared to the bit position of the straight domain wall region, and the sign of the domain wall curvature in the VBL versus regressive transfer path has changed. Therefore, it was difficult to stably transfer the VBL pair within the domain wall at the tip of the domain. Furthermore, during the operation of stretching the tip of the strike domain when writing or reading information, in order to lower the effective bias magnetic field acting on the domain tip, the bulge of the domain tip increases once, and then as shown in Fig. 5. Stretch as shown. This change in the bulge just before the stripe domain extends causes the domain walls at the adjacent bit positions on both sides to move in addition to the bit position at the tip of the domain, causing the VBL there to move.
The driving force also acted on the pair, and as a result, the stability of the VBL pair was threatened.

(Means for Solving the Problems) The present invention provides a structure for forming adjacent striped domains in a Bloch domain wall around a stripe domain existing in a ferromagnetic (including ferrimagnetic) film whose easy magnetization direction is perpendicular to the film surface. Two VBLs
When using a VBL pair consisting of as a storage unit, hollowing out the center of the region where the stripe domain is to be placed, forming a groove, and arranging a closed domain domain wall to surround it, the width d of the groove is defined as the stripe domain. natural width W. This is a magnetic memory element characterized by being larger than that of the magnetic memory element.

The present invention solves the problems of the prior art by adopting the above-described configuration. During stable maintenance and transfer of the VBL pair, as shown in Figure 2, the shape of the tip of the stripe domain reflects the groove shape, and the unique shape of the domain tip, which was exposed in the conventional method, is almost the same as shown in Figure 2. It's completely suppressed. By forming such a domain wall shape, it is possible to easily control the VBL versus drive magnetic field applied from the outside.

As a result, it has become possible to bring the VBL pair transfer conditions closer to the drive conditions of other straight domain wall sections. Furthermore, when writing or reading information, only the vicinity of the tip bit position of the stripe domain can be stretched with good stability, as shown in FIG.

(Example) The structure of the minor lube portion of the striped domain holding layer in the present invention will be described.

FIG. 1 shows the main parts of a striped domain retention layer when using the method of the present invention. Strive domain retention layer 1
A groove 4 is formed in the area where the upper domain is to be held, and an auxiliary groove 6 is formed between areas separated along this groove.

This can be achieved, for example, by etching the trenches in the striped domain retention layer. A domain generator and local in-plane magnetic field generating means 7.8 are arranged at both ends of the groove 4. In addition, domain generators and local magnetic field application means were provided at both ends of the trench for stabilizing the stripe domains, thereby facilitating the desired shape of the domains. Further, by creating the grooved portion 10 for the stripe domain guide, it is possible to reliably extend the stripe domain to the gate portion 11 during write and read operations.

A chip using this stripe domain stabilization method is Gd
5Ga50. (111) 411m bubble material (
A YSmLuCa)3(FeGe), O□2 garnet film was fabricated using a 2 pm thick LPE-length striped domain retention layer. In the chip, the distance between adjacent grooves (corresponding to the distance between bubble domains on the measure line) is set to W in consideration of the stability of transfer of bubble domains on the measure line. It was designed to be three times as large. The radius d of the groove for stabilizing the stripe domain and the natural width W of the stripe domain
When the ratio d/Wo = 1.1, the bias magnetic field range in which the bulge at the domain tip is suppressed was expanded by 1.7 times compared to when d/W = 0.9. Furthermore, d/W = 1
．． When set to s, the bias magnetic field range in which the bulge at the domain tip can be suppressed is d/W. 2 compared to when = 0.9
．． It has expanded five times. However, if d is further increased, d/
When W = 2.1, the stabilizing bias field range of the strive domain decreased sharply. This is because the effective bias magnetic field in the region sandwiched between adjacent grooves has become very high due to the groove effect.

(Effects of the Invention) Conventionally, in order to increase the stripe domain arrangement density, the stripe domain width is a natural width W. (stripe domain width in a state where no external magnetic field is applied to the striped domain holding layer)
is d<W. I chose it to meet the requirements. However, under these conditions, the shape of the stripe domain tips changed sensitively depending on the static bias magnetic field HB applied from the outside in the direction perpendicular to the film surface for stabilizing the stripe domains. H.B.
When the value becomes lower than a predetermined value, the tip of the domain bulges out like the tip of a dogbone, as shown in FIG. With such a domain domain wall shape, when a VBL pair is transferred at the tip of the striped domain, the so-called effective driving magnetic field, which is obtained by correcting the externally applied driving magnetic field by a demagnetizing field from the boundary 5 of the groove 4, corresponds to the bit position at the tip of the domain. In addition, the values of the adjacent bit positions on both sides are greatly different from each other and the bit positions of the straight domain wall region, and the encoding of the domain domain wall curvature between the VBL and the inversion transfer path is different, so the VBL It was difficult to stably transfer the pair within the domain wall at the domain tip. Furthermore, during the operation of stretching the striped domain tips when writing or reading information, in order to lower the effective bias magnetic field acting on the domain tips, the bulge of the domain tips becomes larger, and then the bulge shown in FIG. It stretches like this. This change in the bulge just before the stripe domain extends moves not only the bit position at the tip of the domain but also the domain walls at the adjacent bit positions on both sides, and a driving force also acts on the VBL pair there, resulting in the VBL This threatened the stability of the two countries.

The present invention makes the domain tip shape reflect the groove shape, and almost completely suppresses the domain-specific shape of the domain tip that was exposed in the conventional method. By forming such a domain wall shape, it is possible to easily control the VBL versus drive magnetic field applied from the outside. As a result, it has become possible to bring the VBL pair transfer conditions closer to the drive conditions of other straight domain wall sections. Furthermore, when writing or reading information, it is now possible to stretch only the vicinity of the tip bit position of the above-mentioned stripe domain with good stability. According to the present invention,
The tip of the stripe domain no longer bulges out like the tip of a dogbone due to changes in the static bias magnetic field, greatly improving the reliability of Bloch line memory.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the main structure for holding domains in the present invention, and FIG. 2 is a diagram showing the shape of the tip of a striped domain domain wall surrounding a groove in the present invention. FIG. 3 is a diagram showing the stretching process of the strive domain of the present invention, and FIG.
The figure shows the shape of the tip of the stripe domain domain wall surrounding the conventional grooved part, Figure 5 shows the stretching process of the stripe domain in Figure 4, and Figure 6 shows the conventional stripe domain arrangement method applied. FIG. 3 is a diagram showing grooves and conductor wire arrangement. In the figure, 1... domain holding layer, 2... substrate,
30. . Spacer, 4... Domain holding layer hollowed out part, 5...
Edge of hollowed out part, 6... Auxiliary domain holding layer hollowed out part, 7, 8... Conductor pattern for domain generation and conductor wire for local magnetic field generation, 9... Direction of static bias magnetic field, 10. ... Guard domain holding layer hollowed out part, 11 ... VBL pair write and read gate, 1
2... Major line (bubble transfer path), 13...
Stripe domain, 14... Stripe domain domain wall, 15.15-... Stripe domain domain wall tip,
16... Conductor wire for domain generation, 17... Conductor wire for local magnetic field generation.

Claims (1)

[Claims] In a Bloch domain wall at the boundary of a stripe domain existing in a ferromagnetic (including ferrimagnetic) film that has information reading means, information writing means, and information storage means and whose easy magnetization direction is perpendicular to the film surface. A means is provided to retain and transfer the created pair of two adjacent vertical Bloch lines within the Bloch domain wall, and a groove is provided in the stripe domain retention layer spanning the area where the stripe domain is desired to be placed, and the tip area of the groove is provided. In a magnetic memory element that is equipped with means for generating domains and local magnetic fields, the width of the groove is defined as the natural width of the stripe domain of the stripe domain holding layer (the width of the stripe domain when no external magnetic field is applied to the stripe domain holding layer). A magnetic memory element characterized in that the magnetic memory element is set in a range of 1.0 times to 2 times.