Study of metal-insulator like transition in Co1-xFexS2

The metal-insulator like transition of the ferromagnetic (FM) state in Co1-xFexS2 (0 <= x <= 0.7) with varying x is investigated using X-ray diffraction, Mossbauer spectroscopy, and magnetoresistance measurements. The linear decrease of unit cell parameter with x confirmed Fe substitution at the Co site. The room temperature Mossbauer study showed the absence of magnetic moment on Fe and both isomer shift and quadrupole splitting were found to vary linearly with x. The temperature-coefficient-of-resistivity (TCR) in the FM state became negative for x = 0.15. For intermediate compositions i.e., x >= 0.05 and 0.1, TCR changed from positive to negative (T <= T-C) to positive with an increase in temperature. By studying the temperature-dependent and isothermal magnetoresistance data around the transition region, it was shown that resultant behavior could be arising due to changes in spin polarization over a broad temperature range.