Colossal Magnetoresistance Without Double Exchange Mechanism in Spinel FeCr₂S₄

The crystal structure of spinel FeCr₂S₄, which shows a semiconductor-metal transition and paramagnetic-ferrimagnetic transition at T_c = 170K , was determined by x-ray powder diffraction. It is found that the spinel FeCr₂S₄ belongs to a normal spinel structure Fe²⁺_tCr³⁺_2oS₄. The result clearly shows that the spinel FeCr₂S₄ has neither mixed valence of Fe³⁺ and Fe²⁺ ions or Cr³⁺ and Cr²⁺ ions for a double-exchange magnetic interaction, nor a Jahn-Teller cation such as Cr³⁺. The spinels represent a distinct class of colossal magnetoresistance materials, with magnetic ordering driven by superexchange rather than double exchange.