Application of orthoferrites to domain-wall devices

Abstract

Orthoferrites are of general formula RFeO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> where R is any rare earth or yttrium. They are usually flux grown as large single crystals and then processed to provide platelets several mils in thickness. A high uniaxial anisotropy gives rise to a single unique easy magnetization direction parallel to the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</tex> axis above room temperature in all orthoferrites except SmFeO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> . A low saturation magnetization results from the canting of a pair of anti-parallel spin systems. Platelets prepared so that the easy axis of magnetization is normal to the planar surface display a serpentine domain pattern made visible by the Faraday effect. Under specific conditions cylindrical domains are observed. These domains, which in Sm <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.55</inf> Tb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.45</inf> FeO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> are as small as 0.8 mil in diameter, can be manipulated to perform memory and logic. Three techniques can be used to propagate cylindrical domains. The first uses a sequence of current pulses applied to a conductor array. The second requires an in-plane rotating field acting on a structured Permalloy pattern to generate traveling positive and negative poles. These poles selectively attract and repel a cylindrical domain and thereby control its motion. The movement of an inchworm most closely approximates the propagation mechanism of the third technique. Interacting a pulsating domain with a wedge-like Permalloy pattern results in a unidirectional movement.