Properties and Device Applications of Magnetic Domains in Orthoferrites

Abstract

It has been shown that isolated magnetic domains in thin platelets (≍2 mils thick) of orthoferrites can be manipulated to perform memory, logic, and transmission functions. The purpose of this paper is to discuss the properties of orthoferrites that make them suitable for magnetic device applications and consider magnetostatic problems relevant to domain structures found to be useful. Included is a brief indication of how memory, logic, and transmission can be accomplished; however, the details will be reserved for a later paper. The stability conditions of a cylindrical domain are discussed in detail and data is reported to support the conclusions. Of particular interest are the sizes of cylindrical domains available in the various orthoferrites. Such data has been taken on five of the fourteen possible orthoferrites and it is found that the thulium orthoferrite, TmFeO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> , gives the smallest stable domain diameter (2.3 mils) and LuFeO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> the largest. The stability results lead to a direct method for obtaining σ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</inf> , the domain wall energy density. For TmFeO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> , as an example, σ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</inf> = 2.8 ergs/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . It is concluded that the orthoferrites are well suited indeed for device applications. Experimentally, 3 mil diameter domains have been manipulated and there is every reason to believe that operation of sub-mil domains will soon be realized.