The negative anisotropic magnetoresistance (AMR) effect is observed in pseudo-single-crystal γ'-Fe4N films from 4 to 300 K. Below 50 K, the changes in the AMR ratio depend on the crystal direction along which the sensing current flows. A large stepwise change of the AMR ratio is observed along the [100] direction. The anomalous cos (4θ) component appears on the AMR curves below 30 K. A first-principles calculation of γ'-Fe4N indicates that the electron occupation of the 3d orbitals is modified as the magnetic moment direction changes with respect to the crystal axes. The anomalous behavior of the AMR effect might be due to the change of the partial density of states of 3d-orbitals at the Fermi level.

Negative anisotropic magnetoresistance (AMR) is observed in Fe4N film from 4.2 to 300 K. The AMR ratio rises with temperature in a stepwise fashion near 50 K, and is accompanied by a change in the magnetization hysteresis. The Campbell and Fert model is extended to investigate the influence of spin-polarization of conduction electrons on the AMR, and it is found that the negative AMR is not observed for majority spin conduction in ferromagnets. Consequently, it is concluded that the negative AMR that observed in the present study is possibly clear evidence of minority spin conduction in Fe4N film, as is predicted theoretically.

Pseudo-single-crystal Cu underlayer (UL) with thermal tolerance was obtained on bare Si wafer by employing a diffusion-blocking layer. Fe4N layer fabricated on the Cu UL has an epitaxial relationship and a large grain diameter. Magnetic tunnel junctions in a stacking sequence of Fe4N/MgO/CoFeB exhibited an inverse tunnel magnetoresistance (TMR) effect at room temperature. The largest magnitude of the TMR ratio, −75.1%, was obtained at bias voltage Vb=−250 mV, where electrons flow from CoFeB to Fe4N. The large inverse TMR ratio is due to the improvement of the crystallinity of the Fe4N film because of the small lattice misfit between Fe4N and Cu.

Current-induced magnetization switching (CIMS) in CoFeB (pinned layer)/MgO/Fe4N (free layer) magnetic tunnel junctions (MTJs) was investigated at room temperature and an inverse CIMS phenomenon was clearly identified. From the current-field magnetic phase diagram, determined from the dependence of the switching field on the bias current, the direction of spin-transfer torque was found to be opposite to that observed in CoFeB/MgO/CoFeB-MTJs. The inverse CIMS observed in this study cannot be explained only by the conventional theory, which states that the direction of the spin-transfer torque is determined by the sign of the spin polarization of the pinned layer.

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