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 (HgCr₂S₄, 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 ∼10⁴. The HCS single crystal grown by a newly developed facile method displays similar properties with a larger CMR up to 10⁶–10⁷. 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.