Anisotropic magnetoresistance in Mn 4− x Ni x N and the change in the crystalline field
Résumé
We focus on rare-earth-free anti-perovskite Mn 4− x Ni x N epitaxial films, which can be used for ultrafast current-induced domain wall motion (CIDWM) in magnetic strips. The magneto-transport properties of these materials are very important for a deep understanding of CIDWM. In this study, we investigated the magneto-transport properties of Mn 4− x Ni x N epitaxial films grown on SrTiO 3 (001) and MgO(001) substrates through anisotropic magnetoresistance (AMR) measurements at temperatures between 2 and 300 K. In samples with a small Ni composition such as x = 0.05−0.1, the AMR ratio of Mn 4− x Ni x N drastically decreased with increasing temperature. We also analyzed the twofold and fourfold symmetries in the AMR curves. Fourfold symmetry is caused by tetragonal crystal fields and is unique to anti-perovskite 3 d-metal nitrides such as Mn 4 N and Fe 4 N. Only slight fourfold symmetry was observed in Mn 4− x Ni x N. We also performed first-principles calculations with the Vienna ab initio simulation package (VASP) to obtain the projected density of states (PDOS) of d orbitals in Mn 4− x Ni x N, which is responsible for the magnetism of these materials. We conclude that these results are due to the Ni atoms, which function as magnetic impurities and lead to a noticeable change in PDOS, as proved by VASP calculation.