Asymmetric magneto-optic response in anisotropic thin films

We report asymmetric hysteresis loops measured using the magneto-optic Kerr effect from epitaxial Fe(110) and Co(110) thin films with in-plane magnetic anisotropy. This asymmetry appears to violate the invariance of the hysteresis loop under the transformation M-->-M, H-->-H (M is the magnetization and H is the applied field). The asymmetric magneto-optic response is due to a product of the longitudinal and transverse components of the magnetization and proves the existence of the transverse component of the magnetization and, therefore, of the coherent rotation model of magnetization reversal. We simulate the observed hysteresis loops with a term in the magneto-optic response second order in the magnetization that is much larger than predicted by the standard magneto-optic theory.