Neutron diffraction evidence for common axial-dominant antiferromagnetic order in Fe0.7A0.3Sn (A = Co, Ni)

Abstract

Pristine FeSn is a kagome antiferromagnet whose ordered moments lie predominantly in the basal plane, whereas Co and Ni substitution at the Fe site has been suggested to reorient the Neel vector toward the c-axis. While the magnetic structure of Co-substituted FeSn has been investigated directly, that of Ni-substituted FeSn has remained unresolved. Here, we use neutron powder diffraction to determine the magnetic structures of polycrystalline Fe0.7Co0.3Sn and Fe0.7Ni0.3Sn. In both compounds, the absence of magnetic intensity at (0 0 1/2), together with the emergence of magnetic Bragg peaks at (1 0 1/2) and (2 0 1/2), supports predominantly axial antiferromagnetic order. Temperature-dependent diffraction further reveals subtle anomalies in the lattice parameters near the onset of magnetic intensity, suggesting a weak magnetoelastic response. Rietveld refinements at 4 K yield ordered moments of 1.26(2) mu B/(Fe, Co) and 1.12(7) mu B/(Fe, Ni) for Fe0.7Co0.3Sn and Fe0.7Ni0.3Sn, respectively, indicating suppressed long-range magnetic order relative to pristine FeSn. These results directly demonstrate that Ni substitution, like Co substitution, stabilizes a closely similar axial-dominant antiferromagnetic state in FeSn, accompanied by reduced ordered moments and suppressed ordering temperatures.