Multiple magnetic states and irreversibilities in the FexTiS2 system

The structural and concentration conditionality of magnetic states and transport properties of layered chalcogenide compounds FexTiS2 (0 <= x <= 0.75) have been studied by means of x-ray and neutron diffraction, magnetization, electrical resistivity, and magnetoresistance measurements performed on polycrystalline samples synthesized by solid-phase reaction method with prolonged homogenization heat treatment. It has been revealed that various magnetic states [spin-cluster glass state at x < 0.25, antiferromagnetic (AFM) order at x approximate to 0.25-0.28, cluster glass state at x approximate to 0.33, AFM at x approximate to 0.45-0.5, and ferrimagnetic ordering above x = 0.5] are realized in the FexTiS2 system with increasing Fe content. The absence of a long-range magnetic order in Fe0.33TiS2 is confirmed by neutron diffraction measurements. The magnetic states observed in this system are closely related not only to the concentration of Fe atoms, but also, to a greater extent, to their distribution over the cation layers. It is assumed that the single crystals obtained by chemical vapor deposition are practically unique objects with only their inherent properties, which leads to inconsistency between the literature data on the magnetic properties of these compounds. Changes in the magnetic state of FexTiS2 with Fe concentration are accompanied by nonmonotonic dependencies of the magnetoresistance and coercivity with maximal absolute values in compounds with the AFM virgin state. The ferrimagnetic order in compounds with x > 0.5 is suggested to originate in Fe-Ti mixing in cationic layers. The AFM ordered compounds undergo the field-induced phase transitions to the metastable high-coercive ferromagnetic (FM) state, which is accompanied by a large remnant magnetoresistance. The enhanced coercivity observed in compounds with the AFM virgin state is ascribed to the intrinsic exchange bias together with the Ising-type spin state of Fe ions.