Half-metallic Fe3O4 films prepared by DC magnetron reactive sputtering with a tantalum(Ta) buffer layer was investigated. Primary emphasis is placed on the structural impact on its magnetic properties. The experimental results show that the amorphous Fe3O4 films exhibit a superparamagnetic response at a large-scale from 20 nm to 150 nm, and the magnetoresistance (MR) isn’t detected. By contrast, the polycrystalline Fe3O4 films possess large saturation magnetization Ms of 420 A/(kg·cm) and a clear magnetoresistance with a field of 40 kA/m. The unusual properties for the amorphous Fe3O4 film are attributed to the existing large density of the similar structure as anti-phase boundaries in the film.
Cobalt ferrite thin films were deposited on TbFeCo(10 nm)/Si(100) and Si(100) substrates at a substrate temperature of 350 ℃ by RF magnetron sputtering. The heat treated films were analyzed by Vibrating Sample Magnetometer (VSM) and X-Ray Photoelectron Spectroscopy (XPS). Results showed that all films had high coercivity and perpendicular anisotropy especially for the films deposited on TbFeCo underlayer. TbFeCo underlayers increase the coercivity, magnetization and remanence ratio of CoFe2O4 films, films on TbFeCo underlayer had coercivity and magnetization as high as 832×103 A·m-1 and 450×103 A·m-1, and its romance ratio reaches 0.9, which was related to the Tb3+ diffusion from the underlayer into the film.
Sintered Sm(CobalFexCu0.1Zr0.03)7.5 (x=0.09-0.21) permanent magnets with higher Fe content were found to have higher remanence Br and maximum energy product (BH)max at room temperature. Br and (BH)max reached maximum of 0.96 T and 176.7 kJ/m3, respectively at room temperature when the Fe content x reached 0.21. However, the intrinsic coercivity Hci at room temperature increased gradually when the Fe content x increased from 0.09 to 0.15, but when x further increased to 0.21, Hci decreased. Hci attained its peak value of 2276.6 kA/m with Fe content x=0.15 at room temperature. For magnets with x=0.15, Br, (BH)max and Hci reached 0.67 T, 81.2 kJ/m3 and 509.4 kA/m at 500 °C, respectively, showing good high temperature stability, which could be used in high temperature applications.
The combination of ferromagnetic metal (FM) and semiconductor (SC) for spin injection was studied and demonstrated with FM-SC-FM junction. The semiconductor was chosen to be doped Indium-Tin-Oxide(ITO). Both ITO single-layer film and CoFe-ITO-CoFe junction were sputtering deposited. The ITO single-layer film was n-type with a small resistance of about 100 Ω/Square. I-V curves and Magnetoresistance (MR) effect of the CoFe-ITO-CoFe junction were measured at room temperature and 77 K. Results show that the CoFe forms an ohmic contact to ITO film. But at low temperature, the I-V curves show a Schottky-like characteristic, which is strongly affect by applied magnetic field. The MR effect was measured to be 1% at 77 K, which indicates a spin injection into semiconductor to be realized in this sandwich junction.
