Anomalous Hall effect in polycrystalline Mn₃Sn thin films

A polycrystalline Mn₃Sn thin film was fabricated on a Si/SiO₂ substrate by radio frequency magnetron sputtering with co-deposition from Mn and Sn targets followed by a thermal annealing process in vacuum. From a structural analysis by transmission electron microscopy, the Mn₂Sn phase was found to co-exist in the film. The thin film exhibited weak ferromagnetic behavior, and the saturation magnetization, M_S, of the ferromagnetic component of the Mn₃Sn phase was about 10 emu/cc at room temperature, which is six times larger than the reported value for bulk Mn₃Sn single crystals. M_S significantly increased below 250 K, corresponding to the Curie temperature of Mn₂Sn. An anomalous Hall effect (AHE) was observed in the film in the examined temperature range of 50 K to 350 K. The anomalous Hall conductivity, σ_AH, was negative at room temperature like the bulk Mn₃Sn, and the estimated value of -18.5 Ω^-1·cm^-1 was comparable to that of the bulk Mn₃Sn. The sign of AHE was changed to positive below 240 K, which might be caused by the co-existing Mn₂Sn phase. We thus concluded that a large AHE in antiferromagnetic materials was observed in a thin film form of Mn₃Sn.