JPS622387B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic memory element using cylindrical magnetic domains.

When a magnetic medium with uniaxial magnetic anisotropy such as garnet is grown as a crystal perpendicular to the axis of easy magnetization, and a uniform bias magnetic field of an appropriate magnitude is applied in the direction of the easy axis of magnetization, the periphery and the magnetization change in the magnetic medium. It is known that a cylindrical magnetic domain surrounded by a single domain wall with opposite directions is formed. When a magnetic field gradient is applied to this magnetic medium, the cylindrical magnetic domain can be moved along the magnetic field gradient, and by using this property, it is possible to realize a magnetic memory element. Current drive methods using conductor patterns and magnetic field drive methods using soft magnetic patterns are known as means for applying magnetic field gradients to move cylindrical magnetic domains, but the latter magnetic field drive method is preferred due to its ease of configuration. It is often used. The magnetic field driving method generates and moves magnetic poles that attract cylindrical magnetic domains within a cylindrical domain transfer pattern made of a soft magnetic film such as permalloy provided in the plane of the magnetic media film by applying a rotating magnetic field within the plane of the magnetic media film. In this method, the cylindrical magnetic domain is moved accordingly. The shape of the transfer pattern is determined so that the movement of the magnetic pole is performed in accordance with the direction in which the magnetic field sequentially rotates, and the cylindrical magnetic domain moves in a fixed direction by the repeated pattern. There are already soft magnetic film pattern shapes suitable for this purpose such as T-bar, Y-bar,
Chevron, Y-Y, asymmetrical half-disc shapes, etc. have been devised. The first two have 1 bit and 2 patterns, and the cylindrical magnetic domain passes through two pattern gaps during one cycle of rotation of the rotating magnetic field, whereas the latter three have 1 bit and 1 pattern, and the cylindrical magnetic domain passes through the pattern gap in two places during one cycle of rotation of the rotating magnetic field. It passes through only one pattern gap during one period of rotation. Recently, a transfer pattern consisting of one bit per pattern is often used for the following reasons. The transfer pattern is formed by photolithography, but the diameter of the cylindrical magnetic domain is as narrow as 3 μm or 2 μm, requiring advanced microfabrication technology. Therefore, the minimum pattern gap for a transfer pattern consisting of two 1-bit patterns such as a T-bar is approximately 1/2 that of a transfer pattern consisting of 1-bit 1 pattern such as a chevron, resulting in poor processing accuracy and reproducibility. Therefore, the transfer pattern is becoming less and less used, and a 1-bit 1-pattern transfer pattern with a small pattern gap is often used.

However, even in a transfer pattern consisting of one bit and one pattern, the existence of pattern gaps poses a problem.
In addition to being the most minute part of the transfer pattern, considering the cylindrical magnetic domain transfer operation, it is sensitive to the operating area and pattern defects, and it determines the operating margin and yield of the device. This is because this is the pattern gap. For this reason, transfer patterns have been devised in which the transfer pattern is made asymmetrical to widen the operating area for passing through the gap and the gap is made larger, and the transfer pattern has a gap margin that is resistant to fluctuations, but the gap still exists. The quality of this part determines the characteristics of the element.

An object of the present invention is to provide a cylindrical magnetic domain transfer path without any gaps, and to realize a cylindrical magnetic domain storage element capable of high density, high yield, and low magnetic field driving.

That is, the present invention provides a magnetic medium capable of holding a cylindrical magnetic domain, means for applying a bias magnetic field perpendicular to the film surface of the magnetic medium, means for applying a rotating magnetic field parallel to the film surface of the magnetic medium, and a film of the magnetic medium. In a cylindrical magnetic domain storage element that has functional parts necessary as a storage element on its surface, the position reached by crossing the central axis of the cylindrical magnetic domain transfer path is a position that is earlier than any other position before crossing the central axis of the transfer path. This is achieved by providing a gapless cylindrical domain transfer path that is magnetically close to the magnetic field.

Next, the gist of the present invention will be explained using a pattern based on a chevron shape as an example.

Figure 1 shows a part of a conventional chevron-shaped cylindrical domain transfer path consisting of 1 bit and 1 pattern.
is a chevron pattern made of a soft magnetic film. Figure 2 shows A _i → B _i → C _i → divided into 1/8 periods.
This diagram shows a rotating magnetic field that rotates counterclockwise in the order of D _i → E _i → F _i → G _i → H _i . The suffix i represents the number of periods. If one period is i, the next period is i+1. becomes. The polarity of the bias magnetic field is determined so that the cylindrical magnetic domain is attracted in the direction of the arrow, and the symbols shown in FIGS. 1 and 2 correspond to each other. As can be seen from FIG. 1, the magnetic poles in the chevron pattern 11 generated by the rotating magnetic field are A _i → B _i → C _i → D _i →E _i →F _i →G _i →
They are arranged in the order H _i →, making it possible to transfer cylindrical magnetic domains. FIG. 3 shows a gapless transfer path 31 in which the chevron patterns 11 are simply connected continuously, in the same format as FIG. 1. Along with the rotating magnetic field, the magnetic pole moves as A _i →B _i →C _i →D _i →E _i →F _i →, but since there is no gap, D _i →E _i →F _i
Unlike FIG. 1, the magnetic pole generation positions are arranged in the opposite order to the moving direction of the cylindrical magnetic domain. Therefore, when the rotating magnetic field further advances, the cylindrical magnetic domain passes through G _i ' without passing through G _i and returns to the position of H _{i +1} one cycle earlier, and hereafter A _i → B _i → C _i → Local reciprocating motion of D _i →E _i →F _i →G _i ′→H _i+1 , so-called “idling phenomenon”
It only repeats , but it is not transferred in one direction. When designing a gapless cylindrical domain transfer path, one of the important factors is how to prevent this idling phenomenon.

In the pattern shown in Fig. 3, it is necessary to cross the transfer path center axis 1 to reach from F _i to G _i , but there is no need to cross it to reach G _i ′, so the cylindrical magnetic domain is easily transferred. It moves towards G _i ' and causes an idling phenomenon.

Note that the transfer path center axis refers to a line connecting the centers of the transfer path in the width direction of the gapless transfer path. Generally, in order for a cylindrical magnetic domain to move in a fixed direction in a gapless transfer path, it crosses the center axis of the transfer path twice within one cycle of the rotating magnetic field.The idling phenomenon originally occurs when the cylindrical magnetic domain crosses the center axis of the transfer path. The position to be reached is magnetically equidistant or far away from the previous position before crossing the transfer path central axis compared to any other position, and any other position is closer to the transfer path center axis. This occurs because it is located in a position that can be reached without crossing the road. Therefore, in order to prevent the idling phenomenon, the cylindrical magnetic domain is The pattern should be designed such that it does not cross the central axis of the transfer path, and in the case of crossing the central axis of the transfer path, the position that it should originally move to reach is magnetically sufficiently closer than any other position. I know what I should do. Note that the "magnetic distance" herein refers to a distance that takes into account not only the positional distance r but also the strength M of the magnetic pole of the transfer pattern, and increases in proportion to r ² /M.

Next, details of the present invention will be explained using examples.

FIG. 4 shows a gapless cylindrical magnetic domain transfer path 41 that eliminates the idling phenomenon, and is shown in the same format as FIG. 1. According to this pattern, since the ends corresponding to the gaps in Figure 1 are shifted and connected, when crossing the central axis 1 of the transfer path, C _i → D _i → and E _i → F _i , both of which are relative to any other position. Because the distance is magnetically close, idling phenomenon does not occur and transfer in one direction is possible. One of the gapless transfer paths that has already been devised is a contiguous disk pattern, but in this pattern, the cylindrical magnetic domain is transferred without crossing the center axis of the transfer path. are distinct.

FIG. 5 is a diagram showing the details of a part of the cylindrical domain transfer path in the cylindrical domain storage element according to the present invention, in particular the functional parts necessary for a normal cylindrical domain storage element, the magnetic means for holding the cylindrical domain, and the cylindrical domain transfer path. Magnetic means for transferring magnetic domains have been omitted. Hard bubble suppression treatment was performed on the (Ysmluca) ₃ (FeGe) ₅ O ₁₂ garnet film via a spacing insulating film.
A gapless transfer pattern 51 made of NiFe is formed. The pattern shown in FIG. 5 has been improved so that the transfer operation can be performed more stably. Both patterns are basically based on the same principle.
Since the transfer pattern shown in FIG. 5 has no gaps, the operating bias magnetic field region is expanded, and in particular, the bias upper limit value is significantly improved compared to the pattern with gaps. Furthermore, the driving magnetic field can be reduced, making it possible to save power consumption. Furthermore, the tolerance for defect size was increased and the yield was improved.

The gapless transfer path in the above two embodiments has a so-called asymmetric pattern in which the repeating (bit) unit shape does not have any axis of reflection symmetry.
The pattern is not limited to an asymmetric pattern as long as it is based on the principles of the present invention.

As explained above, according to the present invention, a high-performance, low-cost cylindrical domain storage element can be realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a conventional cylindrical magnetic domain transfer pattern, FIG. 2 is a diagram showing the direction of each 1/8 period of a rotating magnetic field, and FIG. 3 is a diagram cited for explaining the gist of the present invention. FIG. 4 and FIG. 5 are diagrams showing an embodiment of a cylindrical domain storage element according to the present invention. 1... Central axis of cylindrical magnetic domain transfer path, 11... Chevron pattern, 31, 41, 51... Gapless cylindrical domain transfer path.

Claims (1)

[Claims] 1. A magnetic medium capable of holding a cylindrical magnetic domain, means for applying a bias magnetic field perpendicular to the film surface of the magnetic medium, and a functional section necessary as a storage element and a cylindrical domain transfer path on the film surface of the magnetic medium. In the cylindrical magnetic domain storage element, the cylindrical domain transfer path does not include any mirror symmetry axis, interspace, or different film thickness in its repeating unit element, and crosses the central axis of the transfer path to the position that it should originally reach. A cylindrical magnetic domain characterized by having an endless cylindrical magnetic domain transfer path such that the magnetic domain is magnetically closer to the position before crossing the transfer path central axis than the position before one cycle of the repeating unit. memory element.