Magnetic properties of CoFeB films with step-terrace surface morphology

Co₆₀Fe₂₀B₂₀ (CoFeB) films was prepared on a 3° mis-cut (0001) Al₂O₃ substrate by using DC Sputtering, and their magnetic properties were studied. An atomic force microscopy image showed that the CoFeB film had a step-terrace surface, and the magneto-optical Kerr effect measurement suggested that magnetic hysteresis had a clear difference for in-plane direction. CoFeB films had a magnetic easy axis along the longitudinal direction of the step-terrace, and the saturation magnetic field values were about 4.3 Oe for the easy-axis direction and about 48 Oe for the hard-axis direction, which is perpendicular to the step-terrace. CoFeB films had an uniaixal magnetic anisotropy with a period of 180° within the plane. The shape magnetic anisotropy energy in the step-terrace CoFeB film was roughly 2.5 times larger than a depsition magnetic anisotropy energy in a flat surface film. The surface morphology of the step-terrace was maintained up to a thickness of 50 nm, which was about 20 times the step-height, but the effect of the shape magnetic anisotropy decreased with increasing thickness. The direction dependent magnetic hysteresis behavior could be qualitativly explained by using a modified Stoner-Wohlfarth model.