Magnetoresistance in spinel-type Mg_xCu_1-xCr ₂S₄

CuCr₂S₄ shows a p-type metallic conductivity and ferromagnetism with Curie temperatures T_c of 375 K, and exhibit magnetic anomaly at 84 K (= T_m). CuCr₂S₄ exhibits the coexistence of both the ferromagnetism and spin-glass with the irreversible magnetic effect below T_m. The partial 20% Mg-substitution for Cu in CuCr₂S₄ slightly reduces the T_c and T_m. Magnetorsistance of Mg_xCu _1-xCr₂S₄ can be expressed as Δp=aH ²-bHⁿ below T^m. a, b, and n are temperature-dependent adjustable parameters. These unique MR behavior would be attributed to the coexistence of the ferromagnetism and spin-glass-like order below T_m, Mg-substitution decreased the conducting carrier, which forms the conduction band whose orbital motion gave the positive MR contribution. Therefore, Mg-substitution gave smaller positive MR contribution and consequently gave larger negative MR (maximum 7% at 10 K) in Mg _0.2Cu_0.8Cr₂S₄. These results suggest that Cr 3d band filling control can be expected to give functional magnetoelectric transport properties in CuCr₂S4.