Effect of annealing temperature on the structure and properties of co-sputtered Fe-Mn-Sn films near 2:1:1 ratio
Abstract
Research in recent years has focused on the thin-film synthesis of high-quality ternary alloys, identified for their tunable properties and potential in spintronics (e.g., Heusler alloys, Kagome magnets). In a previous study, we identified the conditions for stabilizing Fe2MnSn, a Kagome magnet with a high Curie temperature and magnetic anisotropy. However, ternary phases such as Fe2MnSn are challenging to synthesize and stabilize within a narrow temperature window, as binary and elemental phases can also form during the growth process. To highlight these observations, we investigated the thin film phases in the Fe-Mn-Sn system near the 2:1:1 ratio as a function of annealing temperature, ranging from 400 to 700 C. The elemental Fe, Mn, and Sn targets were pre-calibrated to a close to 2:1:1 ratio and co-sputtered at room temperature, followed by annealing. Two binary hexagonal structures, Fe3Sn2 and Fe5Sn3, along with the elemental Fe phase, are stabilized between 400-550 C, but disappear at 580 C, where Fe2MnSn is the only stable phase. Elemental Mn phase starts to appear starting from 600 C, and becomes dominant by 750 C. Electrical, magnetic and magneto-optical properties are observed to correlate with the structural findings and the best properties are observed in the temperature range where Fe2MnSn is the dominant phase. In general, our study highlights the difficulty in growing phase-pure ternary alloys such as Fe2MnSn, which is very strongly based on precise temperature conditions. We also observed significant disordered growth below 100 nm for Fe2MnSn, implying poor thickness scaling behavior.
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