Improvement of Large Anomalous Hall Effect in Polycrystalline Antiferromagnetic Mn3+x Sn Thin Films

In order to improve the large anomalous Hall effect (AHE) in Mn ₃ Sn thin films, we eliminated the co-existing Mn ₂ Sn phase in the films by changing the composition; 50 nm thick polycrystalline Mn _3±x Sn thin films were fabricated on SiISiO ₂ substrates by the sputtering method followed by a thermal annealing process in vacuum. The film compositions were Mn ₇₀ Sn ₃₀ (sample-A), Mn ₇₅ Sn ₂₅ (sample-B), and Mn ₈₀ Sn ₂₀ (sample-C) in as-deposited state and were slightly changed to be Mn ₇₅ Sn ₂₅ (sample-A), Mn ₇₇ Sn ₂₃ (sample-B), and Mn ₇₈ Sn ₂₂ (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 Mn ₃ Sn phase without passing the crystallization of Mn ₂ Sn phase at 300 °C, differently from the sample-A. The saturation magnetization, MS, of the sample-A significantly increased below 250 K, corresponding with the Curie temperature of Mn ₂ Sn. On the other hand, MS 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, σ _AH , at the room temperature increased in magnitude, as the content of Mn increased. The sign of σ _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 Mn ₂ Sn phase in the Mn ₃ Sn thin films with enlarging the Mn content from the stoichiometry. Consequently, we successfully improved the large AHE in polycrystalline antiferromagnetic Mn ₃ Sn thin films.