Anomalous Magnetic Films

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Abstract
A study of three types of anomalous nickel‐iron magnetic films has been made: high coercive‐force films, which have unusually large hysteresigraph values of wall and rotational coercive forces; rotatable initial‐susceptibility films, for which the value of the initial susceptibility as found from low‐field hysteresigraph measurements is determined by previously‐applied high magnetic fields; and mottled films, whose high‐field hysteresis loops show low remanence and a high wall coercive force, and whose Bitter patterns have a spotted or mottled appearance. Anomalous films have been produced by a variety of techniques. In general, for a given technique, a mild treatment yielded high coercive‐force films, a moderate treatment gave rotatable initial‐susceptibility films, and a drastic treatment produced mottled films. The techniques used were evaporation at slow rates at high substrate temperatures, evaporation on aggregated metal deposits, electroplating on annealed gold films, and annealing normal films. According to a qualitative model postulated to explain these results, these production techniques cause the formation of small, scattered inhomogeneities which have high values of randomly oriented magnetic anisotropy associated with them. As the production technique becomes more drastic, the density and anisotropy values of these anisotropy centers increase, causing the gradual transition from high coercive‐force films through rotatable initial‐susceptibility films to mottled films. It is concluded that inhomogeneous strain in conjunction with magnetostriction is a likely cause of anisotropy centers. It is thought that ``rotatable anisotropy'' films discussed by previous workers are closely related to the films investigated in the present study.

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