The surface magnetic and structural properties of magnetite thin films have been probed by nonlinear second-harmonic generation optical method in high- (centrosymmetric, O-h) and low- (noncentrosymmetric, C-1) temperature phases. A model taking into account the cubic magnetocrystalline anisotropy and magnetic symmetry reduction due to a magnetically modified surface layer is supposed to describe the azimuth variations of the nonlinear response. The metal-isolator transition (Verwey) manifests itself in an increase of nonlinear response (similar to 25%) and a decrease in magnetic contrast (similar to 50%). (C) 2006 American Institute of Physics.
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