Half-Metallic Ferromagnetism and Large Negative Magnetoresistance in the New Lacunar Spinel GaTi₃VS₈

The lacunar spinel compounds GaTi4−xVxS8 (0 < x < 4), consisting of Ti4−xVx tetrahedral clusters, were prepared and their structures were determined by powder X-ray diffraction. The electronic structures of GaTi4−xVxS8 (x = 0, 1, 2, 3) were examined by density functional calculations, and the electrical resistivity and magnetic susceptibility of these compounds were measured. Our calculations predict that GaTi3VS8 is a ferromagnetic half-metal, and this prediction was confirmed by magnetotransport experiments performed on polycrystalline samples of GaTi3VS8. The latter reveal a large negative magnetoresistance (up to 22% at 2 K), which is consistent with the intergrain tunnelling magnetoresistance expected for powder samples of a ferromagnetic half-metal and indicates the presence of high spin polarization greater than 53% in GaTi3VS8.本研究合成了由Ti₄₋ₓVₓ四面体团簇构成的空位尖晶石化合物GaTi₄₋ₓVₓS₈（0<x<4），并通过粉末X射线衍射（powder X-ray diffraction）解析了其晶体结构。针对x=0、1、2、3的GaTi₄₋ₓVₓS₈化合物，本研究通过密度泛函计算（density functional calculations）考察了其电子结构，并测试了该系列化合物的电阻率与磁化率。计算结果预言GaTi₃VS₈为铁磁半金属（ferromagnetic half-metal），该结论通过对GaTi₃VS₈多晶样品开展的磁输运实验得到了验证。实验结果显示，该材料在2 K下可实现最高达22%的超大负磁阻，这与铁磁半金属粉末样品预期的晶粒间隧穿磁阻行为相符，同时表明GaTi₃VS₈中存在超过53%的高自旋极化率。