A Study of Exchange Anisotropy in Co-CoO Evaporated Thin Films

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Abstract
A systematic study of ferromagnetic-antiferromagnetic coupling in Co-CoO evaporated thin films with thicknesses from 300 to 1400 Å has been carried out by measuring hysteresis loops and torque curves in the temperature range from 77 to 630 K. The effect of the cooling conditions on exchange anisotropy is described. The unidirectional anisotropy constant J k is nearly constant (≈0.1±0.05 erg/cm2) for this thickness range. The external magnetic field is not the essential factor responsible for the exchange anisotropy, but it is the ferromagnetic domain state present which is responsible for the observed loop shift as well as rotational hysteresis loss in torque curves. A model is proposed to account for the observed loop shift, which is supported by the domain observation.