摘要
The crystal structure of spinel FeCr_(2)S_(4), which shows a semiconductor-metal transition and paramagnetic-ferrimagnetic transition at T_(c)=170 K,was determined by x-ray powder diffraction.It is found that the spinel FeCi_(2)S_(4) belongs to a normal spinel structure [Fe^(2+)]_(t)[Cr^(3+)_(2)]_(0)S_(4).The result clearly shows that the spinel FeCr_(2)S_(4) has neither mixed valence of Fe^(3+)and Fe^(2+)ions or Cr^(3+)and Cr^(2+) ions for a double-exchange magnetic interaction, nor a Jahn-Teller cation such as Cr^(3+).The spinels represent a distinct class of colossal magnetoresistance materials,with magnetic ordering driven by superexchange rather than double exchange.
基金
Supported in partly by the National Natural Science Foundation under Grant No.KJ951-A1-401,and the National Education Department of China.
