E.Y. Jiang

Fabrication of ultrathin epitaxial γ-Fe2O3 films by reactive sputtering

Ultrathin epitaxial ?-Fe2O3 (0?0?1) and (0?1?1) films are synthesized by reactive sputtering on corresponding MgO substrates. The average roughness of the epitaxial films increases with decreasing film thickness, and that of ~5?nm thick films is ~4.2??. The easy axis of the epitaxial ?-Fe2O3 films is verified to be 1?1?1 by angular dependence of hysteresis loops measured by a vibrating sample magnetometer with a sample rotator. The saturation magnetization of the ultrathin epitaxial ?-Fe2O3 films is close to the bulk value of ~390?emu?cm?3 and independent of film thickness when the thickness is above 5?nm, which is crucial for their practical applications in spin filter devices.

Tunable magnetic and electrical properties of polycrystalline and epitaxial NixFe3-xO4 thin films prepared by reactive co-sputtering

Polycrystalline and epitaxial NixFe3−xO4 (0 ≤ x ≤ 1.03) thin films were fabricated by reactively co-sputtering Fe and Ni targets in a mixed Ar + O2 atmosphere, and the structure, magnetic and magnetotransport properties were investigated systematically. The saturation magnetization and resistivity can be tuned over a wide range. The room-temperature saturation magnetization for the polycrystalline thin films decreases linearly with x from 440 to 230 emu cm−3, due to Ni substitution. For the epitaxial thin films, the saturation magnetization and the resistivity can be tuned in the range 195–340 emu cm−3 and 10−4–10−2 Ω m by Ni substitution and the introduction of Fe vacancies, because both Ni substitution and Fe vacancies can influence the charge carrier density and the double exchange on the B sublattice.

Structure, optical, and magnetic properties of facing-target reactive sputtered Ti1−xFexO2−δ films

Structure, optical, and magnetic properties of the anatase Ti1−xFexO2−δ films fabricated by facing-target reactive sputtering were investigated. Structural analyses indicate that there are no impurity phases in the films and the grain size reaches maximum when Fe content x is 0.017. The optical band gap of the Ti1−xFexO2−δ films decreases with the increasing x. Photoluminescence (PL) spectra show that direct and indirect band-to-band transitions coexist, and the indirect radiative recombination can be regarded as a one photon and two phonon coupling courses. The PL intensity due to oxygen vacancies enhances and the refractive index of the fims increases with the increasing x. The Ti1−xFexO2−δ films exhibit room-temperature ferromagnetism due to the oxygen vacancies.

Characterization of facing-target reactive sputtered polycrystalline Fe3O4 films

Polycrystalline half-metallic Fe3O4 films fabricated by facing-target reactive sputtering were investigated systemically. Structural results reveal that typical Fe3O4 grains were well isolated by grain boundaries and grew with columnar structure. The room-temperature magnetization of Fe3O4 films at 50kOe field is much lower than that of bulk Fe3O4 (471emu∕cm3), due to the presence of strong antiferromagnetic coupling within grain boundary and the amorphous bottom and top layers. The insaturation magnetization and loop shift in high field region at low temperature also stem from the strong antiferromagnetic coupling. The resistivity increases with the decreasing temperature and is consistent with fluctuation-induced tunneling mechanism in a wide temperature ranging from 50to300K. The negative magnetoresistances up to −9.7% at 150K and −6.4% at 300K under 90kOe magnetic field perpendicular to the film plane were observed and discussed.