L21 ordering of Co2FeSn thin films promoted by high-temperature annealing

We report the effect of annealing on the crystalline ordering and physical properties in thin films of a nodal line semimetal candidate L21-type Co2FeSn. The Co–Fe–Sn films with a composition of Co:Fe:Sn ∼ 2:1:1 were deposited on MgO(001) substrates at a substrate temperature of 150 °C by radio-frequency magnetron sputtering. The as-deposited film showed x-ray diffraction patterns corresponding to the B2 ordering. Annealing at 600 and 700 °C after the deposition resulted in the appearance of the (111) diffraction peak, which is characteristic of the L21 ordering. Although anomalous Hall conductivity and transverse thermoelectric conductivity decreased from those of the as-deposited film with the annealing-induced L21 ordering, the low anomalous Hall conductivity of the 700 °C-annealed film was consistent with the theoretically estimated low value. These results show the significant influence of crystalline ordering on the electrical and thermoelectric transport properties. The annealing process is beneficial for studying the exotic physics arising from topological band features in the L21-ordered Co2FeSn thin films.