Annealing influence on magnetic anisotropies of CoFe thin films

Post-annealing effect on the magnetic anisotropies of cubic CoFe films epitaxially grown on MgO (001) substrates are investigated. X-ray diffraction patterns reveal that the crystallization degree gradually improves with the increase of annealing temperature (Ta), which results in obvious enhancement in both the uniaxial (HU) and biaxial magnetic anisotropy fields. Magnetic hysteresis loops of the unannealed sample show two equivalent easy axes along the CoFe [110] and [11¯0] directions, being in accord with the observed fourfold symmetry of angular remanent magnetization (ARM) curve. Nevertheless, with the increase of Ta, the two easy axis loops become inequivalent due to the increased HU along [110] direction, thus giving rise to a two-step switching behavior for the [11¯0] direction loop at Ta>350°C and the ARM curve transformation from fourfold to twofold symmetry. This work provides a deep insight and an effective approach to control the magnetic anisotropies and magnetization states for practical ap...