Field-induced spin-flop in antiferromagnetic semiconductors with commensurate and incommensurate magnetic structures: Li₂FeGeS₄ (LIGS) and Li₂FeSnS₄ (LITS)

Li₂FeGeS₄ (LIGS) and Li₂FeSnS₄ (LITS), which are among the first magnetic semiconductors with the wurtz-kesterite structure, exhibit antiferromagnetism with T_N 6 and 4 K, respectively. Both compounds undergo a conventional metamagnetic transition that is accompanied by a hysteresis; a reversible spin-flop transition is dominant. On the basis of constant-wavelength neutron powder diffraction data, we propose that LIGS and LITS exhibit collinear magnetic structures that are commensurate and incommensurate with propagation vectors k_m = [¹/₂, ¹/₂, ¹/₂] and [0, 0, 0.546(1)], respectively. The two compounds exhibit similar magnetic phase diagrams, as the critical fields are temperature-dependent. The nuclear structures of the bulk powder samples were verified using time-of-flight neutron powder diffraction along with synchrotron X-ray powder diffraction. ⁵⁷Fe and ¹¹⁹Sn Mössbauer spectroscopy confirmed the presence of Fe²⁺ and Sn⁴⁺ as well as the number of crystallographically unique positions. LIGS and LITS are semiconductors with indirect and direct bandgaps of 1.42 and 1.86 eV, respectively, according to optical diffuse-reflectance UV-vis-NIR spectroscopy.