Substitution effects on the magnetic properties of Fe-containing chalcogenides with NiAs-type structures

The changes in the magnetization processes caused by Se for S substitutions in the layered chalcogenide compounds Fe_{x}TiS_{2-y}Se_{y} (x=0.5, 0.66) with antiferromagnetic (AF) and ferrimagnetic (FI) orderings, respectively, have been studied by using the magnetization and magnetoresistance measurements. Unusually high values of the coercive fields (H_{c} up to 56 kOe) have been observed at low temperatures in Fe_{0.5}TiS_{2-y}Se_{y} with the Se content y<0.5, which is ascribed to the presence of an unquenched orbital moment on Fe ions and to the formation of a magnetically heterogeneous state in the vicinity of H_{c}. The Se for S substitution in Fe_{0.66}TiS_{2-y}Se_{y} leads to the transition from the FI to AF state and to non-monotonous change of H_{c} with a maximal value 22 kOe an y=0.5. The changes in the magnetic state of Fe_{x}TiS_{2-y}Se_{y} are suggested to be strongly affected by the distribution of Fe ions and vacancies in cationic layers.