Abstract
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.
Highlights
Spin-transfer-torque[1] magnetic random-access memories (STT-MRAMs) are expected to serve as nonvolatile memories with fast operation speeds and infinite read-write endurances.[2,3] Generally, magnetic tunnel junctions (MTJs) composed of ferromagnetic electrodes, with perpendicular magnetic anisotropy (PMA), are utilized for the memory cells of STT-MRAMs
The anomalous Hall effect (AHE) has only been reported for Mn4N thin films fabricated via the pulse laser deposition (PLD)[8] and molecular beam epitaxy (MBE) methods,[9] where there is a one-order of magnitude discrepancy in the anomalous Hall conductivity between the results obtained using these two deposition methods
Taking into account the aforementioned explanation for Fe4N thin films, it is expected that the origin of the low-temperature anomaly of the Mn4N film is attributed to the tetragonal crystal field effect
Summary
Spin-transfer-torque[1] magnetic random-access memories (STT-MRAMs) are expected to serve as nonvolatile memories with fast operation speeds and infinite read-write endurances.[2,3] Generally, magnetic tunnel junctions (MTJs) composed of ferromagnetic electrodes, with perpendicular magnetic anisotropy (PMA), are utilized for the memory cells of STT-MRAMs. an increase in the capacity of the STT-MRAMs strongly requires improving the magnetic and magneto-transport properties of the ferromagnetic materials used in MTJs. an increase in the capacity of the STT-MRAMs strongly requires improving the magnetic and magneto-transport properties of the ferromagnetic materials used in MTJs These improvements involve reducing the STT switching current,[4] and increasing their tunnel magnetoresistance ratio, thermal stability,[5] and PMA.[6] Spintronics materials with low saturation magnetization, and high spin polarization, are expected to satisfy these demands. The anomalous Hall effect (AHE) has only been reported for Mn4N thin films fabricated via the pulse laser deposition (PLD)[8] and molecular beam epitaxy (MBE) methods,[9] where there is a one-order of magnitude discrepancy in the anomalous Hall conductivity between the results obtained using these two deposition methods
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