Magneto-transport properties of pseudo-single-crystal Mn4N thin films

The anisotropic magnetoresistance (AMR) effect and the anomalous Hall effect (AHE) were investigated in the temperature range of 5–300 K for a pseudo-single-crystal Mn4N thin film. The sign of the AMR ratio changed from positive to negative when the temperature was lowered. Below 100 K, the cos 2θ component of the AMR curves significantly increased in magnitude, and a cos 4θ component appeared. Based on the electron scattering theory, which takes into account the tetragonal crystal field effect, it is suggested that the dominant scattering process in the Mn4N film is up-spin conduction electrons into up-spin d orbitals. The magnitude of the anomalous Hall conductivity (σAH) slightly increased with decreasing temperature, from 300 K to 150 K, and then it drastically dropped when the temperature was below 100 K. A sign change for σAH, from negative to positive, was observed at 30 K. The starting temperature at 100 K for the drastic change in the AHE corresponds well with that of the AMR, suggesting that the splitting of the 3d orbitals due to the tetragonal crystal field effect causes these low-temperature anomalies.