Magnetodielectric Effect in Crystals of the Noncentrosymmetric CaOFeS at Low Temperature

Single
crystals of the stoichiometric iron calcium oxysulfide CaOFeS have
been grown by a solid-state reaction. Structural analysis of CaOFeS
at room temperature by combining single-crystal X-ray diffraction
data and transmission electron microscopy leads to a stoichiometric
hexagonal noncentrosymmetric P63mc layered structure isostructural to CaOZnS. It is built
from alternating layers made of FeOS3 tetrahedra sharing
sulfur apexes and stacked with Ca2+ planes. All Fe–O
bonds are parallel to the stacking axis; this breaks the centrosymmetry,
leading to a polar structure. The dielectric measurements reveal the
existence of a magnetodielectric effect near 33 K in good agreement
with the Neel temperature, as evidenced near 35 K by specific heat
measurements reported by a different group.