Hall and Faraday Effects in Oriented MnBi Films

Hall coefficients and resistivity have been measured over the temperature range 77° to 300°K on polycrystalline MnBi films prepared with the c axis of the crystallites normal as well as parallel to the plane of the film. The Hall resistivity follows the well-known relation ρH = R0H+MR1, where R0 and R1 are the ordinary and extraordinary Hall coefficients and M is the magnetization. At room temperature, R0 is 6×10−3 cm3/C for both types of films and R1 is 7×10−2 and 2.5×10−1 cm3/C for the perpendicular and parallel films, respectively. Measurements of the magneto-optic Faraday rotation of perpendicular films indicate that the Faraday rotation is directly proportional to the magnetization. Over the visible wavelength region, the Faraday rotation was found to increase as temperature decreases from 300° to 87°K, by a factor less than 25%. The specific rotation for a typical magnetically saturated film was 1.4×105 deg/cm at the 6328-Å He–Ne laser line at room temperature. Our measurements are in agreement with Goodenough's suggestion of metallic conductivity resulting from a d band formed from the transition metal cations with the assistance of large numbers of interstitial cations. An effective hole density of 1021 cm−3 and Hall mobility of approximately 10 cm2/V-sec characterize these films.