Temperature Dependence of the Magneto-Optic Effect and Resonance Phenomena in Oriented MnBi Films

Abstract

Oriented MnBi films exhibit extremely large magneto-optic Kerr rotation and crystalline anisotropy energy at room temperature. These physical properties are examined experimentally over a range of temperature from 300° to 84°K. The samples studied are polycrystalline thin MnBi films with the c axis of the crystallites oriented perpendicular to the plane of the film. The magneto-optic Kerr rotation is measured with a 6328-Å He–Ne laser source. As the temperature decreases from 300° to 84°K, the following experimental results are obtained: (1) the Kerr rotation decreases by a factor of 32 when the film is in the remanent state; (2) the Kerr rotation increases by a factor of 10 when the film is in the saturation state; (3) the resistivity decreases by a factor of 2; and (4) the reflected light intensity decreases by a factor of 6. The ferromagnetic resonance absorption at 9.02 Gc/sec is observed in the temperature range between 170° and 84°K, with the direction of the external dc field both perpendicular and parallel to the c axis of the film. The anisotropy constant estimated from the FMR data decreases from 4.5×106 erg/cm3 at 162°K to zero at 84°K. This temperature dependence is in good agreement with Guillaud's result calculated from magnetization measurements. The spectroscopic splitting factor g is estimated to be 2.1 at liquid-nitrogen temperature, which is smaller than the previously reported value.