Magnetic phase transitions, metastable states, and magnetic hysteresis in the antiferromagnetic compounds Fe0.5TiS2-ySey

The phase transitions and magnetization processes in the antiferromagnetic compounds Fe0.5TiS2-ySey [FeTi2(S,Se)(4)] with an ordered layered crystal structure of the Cr3S4 type have been studied by using x-ray diffraction, measurements of the specific heat, electrical resistivity, magnetoresistance, and the magnetization in steady and pulsed magnetic fields together with calculations within the Ising model accounting the magnetoelastic interactions. The change from the spin-flip to spin-flop type phase transition and a monotonic growth of the critical transition field from similar to 50 kOe at y = 0 up to 470 kOe at y = 2 has been observed with the Se for S substitution in antiferromagnetic (AFM) compounds Fe0.5TiS2-ySey. In the selenium-poor compounds (y < 0.5), the field-induced AFM-FM phase transition at low temperatures is accompanied by ultrasharp changes in the magnetization and magnetoresistance and by huge magnetic hysteresis. The presence of remnant magnetoresistance in these compounds after the application of a magnetic field indicates the formation of a metastable field-induced FM state. Despite an AFM ground state, the Fe0.5TiS2-ySey compounds with y < 0.5 after application of a magnetic field behave at low temperatures as high-anisotropic Ising-type ferromagnets with the coercive field H-c up to similar to 60 kOe. It has been shown, that magnetoelastic interactions may be responsible for the formation of the metastable field-induced high-coercive FM state in the Ising-type antiferromagnets.