Thermal annealing and magnetic anisotropy of NiFe thin films on n+-Si for spintronic device applications

Abstract

To ensure that the magnetic metal electrodes can meet the requirements of the spin injection, NiFe films prepared both on HfO2 dielectric layer and n+-Si directly by sputtering deposition, and treated by conventional furnace annealing and/or high vacuum magnetic field annealing were investigated. It was found that thermal annealing at 250°C improved the crystalline quality and reduced surface roughness of the NiFe films, thus enhancing its saturation magnetization intensity. The 100nm thick NiFe films had too large coercive force and saturation magnetization intensity in vertical direction to meet the requirements of Hanle curve detection. While, 30nm thick NiFe films showed paramagnetic hysteresis loops in vertical direction, and the magnetization intensity of the sample after annealing at 250°C for 30min was less than 2% to the parallel when the external magnetic field was given between ±10Oe. This was preferred to Hanle curve detection. The thin HfO2 dielectric layer between metal and Si partially suppressed the diffusion of Ni in NiFe into Si substrate and formation of NiSi, greatly enhancing the saturation magnetization intensity of the Al/NiFe/HfO2/Si sample by thermal annealing. Those results suggest that Al/NiFe/HfO2/Si structure, from the point view of magnetic electrodes, would be suitable for spin injection and detection applications.