Ferrimagnetic Mn4N (Fig. 1) is a promising candidate for various spintronics devices thanks to their small magnetization (Ms ~ 100 kA/m) and clear perpendicular magnetic anisotropy (Ku = 0.1 MJ/m)1. Ni-2,3 and Co-doped4 Mn4N films have magnetic compensation (MC) points. Using Ni-doped Mn4N films at the vicinity of the MC composition, our group demonstrated ultrafast domain wall motion (vDW = 3,000 m/s5) driven only by spin-transfer torque at RT thanks to the compensation. Additionally, In-doped Mn4N6 films show ferromagnetism. In this work, we focus on Sn-doped Mn4N (Mn4−xSnxN) film. Although the MC in Mn4−xSnxN bulks was reported at low temperature7, no studies have been reported on MC of Mn4−xSnxN films. Therefore, we fabricated Mn4−xSnxN epitaxial films and evaluated their properties.
25-nm-thick Mn4−xSnxN epitaxial films (x = 0.0–1.0) were grown on the MgO(001) substrates by plasma-assisted molecular beam epitaxy. Both the longitudinal and transverse resistivities (ρxx & ρxy) were measured with van der Pauw method at RT. The ordinary Hall coefficient (RH) was calculated from the slope of the ρxy-μ0H loops at high field regime. The anomalous Hall resistivities ρAH were derived by excluding the component of ordinary Hall effect from ρxy.
Fig. 2 shows the ordinary Hall coefficient (RH) and the anomalous Hall angle (θAH (= ρAH/ρxx)) of Mn4−xSnxN films as a function of Sn composition, x. xcc is the composition where the sign of RH reversed. It suggests that the dominant career-type changed from electrons (RH < 0) to holes (RH > 0) with increasing x. Moreover, the sign reversal of θAH was observed twice at the composition except xcc, indicating it was not caused by change in the career-type. Although similar results were also obtained in Ni-2, Co-4 and In-6 doped Mn4N, this was the first report that the multiple sign reversals of θAH were confirmed in Mn4N-based compounds. The origin seems to be the change of magnetic structures such as MC and ferrimagnetic-to-ferromagnetic transition.
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