Improvement of Large Anomalous Hall Effect in Polycrystalline Antiferromagnetic Mn_3+xSn Thin Films

In order to improve the large anomalous Hall effect (AHE) in Mn₃Sn thin films, we eliminated the co-existing Mn₂Sn phase in the films by changing the composition; 50 nm thick polycrystalline Mn_3+xSn thin films were fabricated on Si/SiO₂ substrates by the sputtering method followed by a thermal annealing process in vacuum. The film compositions were Mn₇₀Sn₃₀(sample-A), Mn₇₅Sn₂₅(sample-B), and Mn₈₀Sn₂₀(sample-C) in as-deposited state and were slightly changed to be Mn₇₅Sn₂₅(sample-A), Mn₇₇Sn₂₃(sample-B), and Mn₇₈Sn₂₂(sample-C), respectively, after the annealing at 500 °C. From a structural analysis by X-ray diffractometry, the sample-C was considered to crystallize to Mn₃Sn phase without passing the crystallization of Mn₂Sn phase at 300 °C, differently from the sample-A. The saturation magnetization, $M-{\mathrm {S}}$, of the sample-A significantly increased below 250 K, corresponding with the Curie temperature of Mn₂Sn. On the other hand, $M-{\mathrm {S}}$ did not show significant changes with cooling temperature in the samples-B and-C. An AHE was observed at the room temperature in all the samples. The anomalous Hall conductivity, $\sigma-{\mathrm {AH}}$, at the room temperature increased in magnitude, as the content of Mn increased. The sign of $\sigma-{\mathrm {AH}}$ changed from negative to positive in the sample-A with cooling temperature. On the other hand, the sign remained negative in the sample-C. These differences might be due to the elimination of co-existing Mn₂Sn phase in the Mn₃Sn thin films with enlarging the Mn content from the stoichiometry. Consequently, we successfully improved the large AHE in polycrystalline antiferromagnetic Mn₃Sn thin films.