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.

We report an effect of field cooling direction on the magnetoresistance of ring-shaped magnetic tunnel junctions consisting of Ta 5/Cu 20/ Ta 5/NiFe 2/Cu 5/MnIr 10/CoFe 4/Al-N 1.5/CoFe 4/NiFe 20/Ta 5-cap (thickness in nm). The magnetoresistances were both enhanced, in comparison to the as-fabricated ring device, with field-cooling directions applied in the film plane as well as perpendicular to the film plane but with greater increase in the case of perpendicular-field-cooled. Many cycles of planar-and perpendicular-field-cooled alternately gave the same results. The greater enhancement of magnetoresistance is shown to be due to the formation of an onion like magnetization configuration in the pinned layer after perpendicular-field-cooled, resulting in a better relative magnetization alignment between the pinned layer and the free layer in the minor loop region. Magnetic force microscopy (MFM) was undertaken to reveal the uniform and onion like magnetization configurations in the pinned layer of ring devices with the same dimensions, but with layer structures of Ta 5/NiFe 2/Cu 5/MnIr 10/CoFe 4/Cu 1/Ta 1 (thickness in nm) for the planar-and perpendicular-field-cooled, respectively. In addition, size-dependent behavior was explored and the results show that the formation of onion like magnetization after perpendicularfield-cooled is associated with the strong shape anisotropy in the narrower linewidths of ring devices.