Crystal structure, magnetic state and electrical resistivity of Fe2/3Ti(S,Se)2 as affected by anionic substitutions

Abstract

The layered compounds Fe2/3TiS2−ySey (0 ⩽ y ⩽ 2) have been synthesized and studied by means of x-ray diffraction, magnetization, electrical resistivity and magnetoresistance measurements in order to reveal how the Se for S substitution affects the crystal structure and properties of these materials. Together with the growth of the unit cell volume the replacement of S by Se in Fe2/3TiS2−ySey leads to anisotropic deformations of the crystal lattice assumingly due to the formation of Fe chains in the ab plane of the crystal lattice and a higher polarizability of Se. The Fe2/3TiS2 compound shows the magnetization behavior characteristic for the highly anisotropic ferrimagnetic materials, while the Se for S substitution leads to an antiferromagnetic ordering in Fe2/3TiS2−ySey at y > 0.5, which is attributed to increasing randomness in the distribution of Fe atoms and vacancies in cationic layers. At low temperatures, the sulfur rich Fe2/3TiS2−ySey compounds exhibit increased magnetic hardness (Hc ~ (8–22) kOe). Unlike antiferromagnetic Fe1/2TiS2−ySey compounds with a metallic-type resistivity behavior the electrical resistivity of Fe2/3TiS2−ySey in the magnetically ordered state is observed to be higher than in the paramagnetic state. An additional magnetic contribution to the resitivity which does not vanishes at T → 0 is ascribed to the appearance of the magnetic-polaron-like states in compounds due to the the partial Fe–Ti mixing in cationic layers.