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Angular Momentum Compensation in Bubble Domain Devices

IP.com Disclosure Number: IPCOM000084345D
Original Publication Date: 1975-Oct-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 4 page(s) / 33K

Publishing Venue

IBM

Related People

Malozemoff, AP: AUTHOR [+2]

Abstract

Bubble domain devices generally employ ferromagnetic materials, such as mixed rare earth iron garnets or amorphous materials such as GdCo. These materials often exhibit a magnetic compensation point which is a temperature at which the magnetizations of the various sublattices in the material exactly cancel each other, so that the net magnetization is zero.

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Angular Momentum Compensation in Bubble Domain Devices

Bubble domain devices generally employ ferromagnetic materials, such as mixed rare earth iron garnets or amorphous materials such as GdCo. These materials often exhibit a magnetic compensation point which is a temperature at which the magnetizations of the various sublattices in the material exactly cancel each other, so that the net magnetization is zero.

If the gyromagnetic ratios of the different sublattices are different, an angular momentum compensation can occur at a temperature T(CJ) which is different from the magnetic compensation temperature T(CM). Bubble domains cannot exist at T(CM), but can exist at the angular momentum compensation point provided that T(CJ) not = T(CM).

It is proposed to use magnetic bubble domains at an angular momentum compensation point to eliminate velocity saturation effects and dynamic conversion, to stabilize bubble domain wall states for information storage systems, and to improve bubble domain manipulation in apparatuses such as bubble lattice files.

In a previous article by B.A. Calhoun, IBM Technical Disclosure Bulletin, Vol. 13, No 6, November 1970, page 1576, it was proposed that the mobility of a bubble domain material would become very large when the material was at an angular momentum compensation point. In the present proposal, it has been recognized that the mobility would not be very different from the usual mobility. Nevertheless, it has been recognized that angular momentum compensation can be used advantageously in all types of bubble domain devices, including bubble domain devices such as the bubble domain lattice file where information is stored in the wall properties of the magnetic domains. DEVICE APPLICATIONS OF ANGULAR MOMENTUM COMPENSATION. 1. Elimination of velocity saturation and dynamic conversion.

Although many garnets have a high mobility, these same materials show a velocity saturation which sets in at a low-threshold field. This velocity saturation is one of the effects that limits the operating speed of a device. The other effect is the creation of hard bubbles by dynamic conversion, which also occurs most noticeably in high-mobility materials.

Both velocity saturation and dynamic conversion are believed,'on a theoretical basis, to be due to nonlinearities in the domain wall velocity, which arise from precession by 180 degrees or more of the domain wall magnetization around the applied field direction (J. C. Slonczewski, J. Appl. Phys. 44, 1759 (1973)). The threshold field for the precession usually goes down as the linear mobility goes up. However at the angular momentum compensation point, the threshold field is predicted to become very large without any significant reduction in the linear mobility.

This means that hard bubbles can no longer be generated (e.g., by dynamic conversion). Thus, extra processing steps such as ion implantation or double- layering which are used to suppress hard bubbles, can be avo...