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

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 $\frac{3}{2}$ 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.