Rotatable anisotropy in epitaxial exchange-biased materials revealed by Brillouin light scattering

Rotatable anisotropy in exchange-biased CoOCo epitaxial films deposited on oriented single crystalline MgO(100) and MgO(110) substrates has been discussed. It has been shown that the rotatable anisotropy, usually observed in ferromagnetic resonance experiments in polycrystalline exchange-biased materials, can also be seen by Brillouin light scattering. Appropriate analysis on the basis of the second derivative of the free energy density for nonbiased and biased systems, i.e., in temperatures below and above the Ńel temperature of CoO, has been performed. A quantitative measure of the rotatable anisotropy was proposed. It has been shown that the rotatable effect, being independent from in-plane orientations, can be tailored by different types of anisotropy fields expressed in terms of effective anisotropy constants.