Magnetic Studies on Quaternary Iron Sulfides BaLn2FeS5 (Ln = Ce, Pr, Nd, Sm) by Magnetic Susceptibility, Specific Heat, 57Fe Mössbauer Spectrum, and Neutron Diffraction Measurements

Magnetic properties of quaternary iron sulfides, BaLn2FeS5 (Ln = Ce, Pr, Nd, Sm), have been investigated through magnetic susceptibility, electrical resistivity, specific heat, 57Fe Mössbauer spectrum, and powder neutron diffraction measurements. In these compounds, the Fe2+ ion exhibits an antiferromagnetic ordering at around 40 K. In the Nd and Sm compounds, these lanthanide ions show an antiferromagnetic ordering at 6.5 K for Ln = Nd and at 28 K for Ln = Sm. The reduction of the Fe2+ magnetic moment is observed below 120–170 K for all the compounds. Their electrical conductivities show an Arrhenius temperature-dependence, and the activation energies change at around the moment-reduction temperatures. The 57Fe Mössbauer spectra for BaPr2FeS5 indicate that the FeS4 tetrahedron is distorted prominently below the temperature at which both the magnetic susceptibility and the electrical resistivity show an anomaly in their temperature dependence. The neutron diffraction data collected for BaPr2FeS5 at 10 K show that it has a collinear antiferromagnetic structure and that the magnetic moments of the Fe2+ ions are parallel to the c-axis.