Field-Induced Spin-Flop in Antiferromagnetic Semiconductors
with Commensurate and Incommensurate Magnetic Structures: Li<sub>2</sub>FeGeS<sub>4</sub> (LIGS) and Li<sub>2</sub>FeSnS<sub>4</sub> (LITS)
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Abstract
Li<sub>2</sub>FeGeS<sub>4</sub> (LIGS) and Li<sub>2</sub>FeSnS<sub>4</sub> (LITS), which are among the first magnetic semiconductors with the
wurtz-kesterite structure, exhibit antiferromagnetism with <i>T</i><sub>N</sub> ≈ 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 <b>k</b><sub>m</sub> = [<sup>1</sup>/<sub>2</sub>, <sup>1</sup>/<sub>2</sub>, <sup>1</sup>/<sub>2</sub>] 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. <sup>57</sup>Fe and <sup>119</sup>Sn Mössbauer spectroscopy confirmed
the presence of Fe<sup>2+</sup> and Sn<sup>4+</sup> 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