Zero-field relaxation and exchange interactions in magnetic thin films

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Abstract
A zero-field relaxation phenomenon has been observed and studied in a series of CoPtCrB thin-film samples with progressively decreasing grain size. In particular, a nonmonotonic time dependence of the magnetization has been measured in zero external magnetic field after partial dc demagnetization of the samples. The zero-field relaxation rate becomes increasingly strong as grain sizes approach the superparamagnetic limit. The phenomenon is ascribed to a cooperative influence of intergranular interactions and thermal effects and is described using an extended Preisach-type model that includes thermal relaxation effects.