Microstructure, magnetic and electronic transport properties of polycrystalline γ′-Fe4N films

The single-phase γ′-Fe4N films were fabricated using reactive sputtering. The x-ray diffraction peaks from γ′-Fe4N(111), (200) and (311) indicate that the films are γ′-Fe4N. The grain size increases with the increase of film thickness (t), and the grains grow with a columnar structure. All of the films are soft ferromagnetic at room temperature. The saturation magnetization decreases with the increasing temperature, and satisfies the modified Bloch's spin wave theory. The electrical transport properties show a metallic conductance mechanism, and the room-temperature resistivity decreases with the increasing t, revealing that the electron scattering increases with the decrease of t. The magnetoresistance (MR) evolves from positive to negative with the increase of temperature, and the transition temperature decreases with the increase of t. The positive MR at 5 K increases with the increasing t. The complex MR should be dominated by Lorentz force effect, the suppression of the electron scattering, and the shift of minority and majority spin bands under a magnetic field.

► The single-phase γ′-Fe4N films were fabricated using reactive sputtering. ► The size of columnar grain increases with film thickness. ► The saturation magnetization satisfies the modified Bloch's spin wave theory. ► The films show a metallic conductance mechanism and a complex magnetoresistance.