Magnetic Field-driven Insulator-Metal Transition and Colossal Magnetoresistance of Metamagnetic Semiconductor Mercury Thiodichromite Crystals.

A facile method is developed to efficiently prepare metamagnetic mercury thiodichromite (HgCr 2 S 4 , HCS) polycrystals and single crystals, and their transport properties are studied. The resistivity of the as-prepared HCS polycrystal shows a semiconducting behavior and no magnetic field dependence in the whole temperature range. In contrast, the annealing treatment of the HCS polycrystal induces gigantic changes: an insulator-metal transition is driven by a magnetic field of 5 T, leading to colossal magnetoresistance (CMR) as high as ∼10 4 . The HCS single crystal grown by a newly developed facile method displays similar properties with a larger CMR up to 10 6 -10 7 . First-principles calculation demonstrates a large spin splitting of band structures, providing the possibility of magnetic polaron existence, which is further evidenced by electron spin resonance spectra. Thus, the insulator-metal transition and CMR can be explained in a magnetic polaronic scenario. This work opens a new window for CMR-based spintronics.