Molecular Beam Epitaxy Growth of Co₂FeSn: a Heusler Nodal Line Semimetal Candidate with Theorized Giant Room Temperature Anomalous Transport

Recently there has been a surge of interest in the giant Anomalous Nernst Conductivity (ANC) and Anomalous Hall Conductivity (AHC) deriving from the topological features in topological semimetals such as ferromagnetic Weyl semimetals and nodal line semimetals due to their potential uses in various device proposals. However in most samples studied to date, the Curie temperature is well below room temperature, limiting their practical applications. Heusler compounds can solve this issue and others as they generally have large Curie temperatures and anomalous Hall angles. The ferromagnetic full Heusler Co₂FeSn has much potential with a large magnetic moment and predicted giant nodal-line-induced AHC and ANC (the largest among the often studied Heuslers) available within a reasonable distance from the Fermi level [1]. Here we report molecular beam epitaxy growth and optimization of the Heusler compound Co₂FeSn(001) on MgO- and Cr-buffered MgO(001). We have confirmed the metastable nature of Co₂FeSn through observation of phase separation at moderate growth temperatures, which limits the ordering of the film. Indeed, Co₂FeSn films show varying degrees of Fe-Sn site disorder depending on growth conditions. Adoption of a chromium buffer leads to an enhancement of the crystalline quality and reduced Fe-Sn disorder, but also enhances other site disorder. SQUID magnetometry further measures a large saturation moment (5.2 μ_B/f.u.) which is slightly reduced from the theorized value (5.6 μ_B/f.u.), suggestive of this disorder. In this talk, we also discuss magnetotransport and thermal transport of the highest quality samples in comparison with first principles calculations.<br/><br/>[1] Noky, et al. npj Comput Mater 6, 77 (2020).