Critical behavior of single crystal CuCr2Se4-x Br x (x=0.25)

The doping of bromine has prominent effect on the transport properties of CuCr2Se4, where the conductivity of CuCr2Se4-x Br (x) changes from metallic behavior with x=0 to semiconductor with x=1. In this work, the critical behavior of single crystal CuCr2Se4-x Br (x) with x=0.25, which lies at the boundary between the metallic and insulating state, is investigated through the magnetization under high magnetic field. The critical exponents beta=0.39 +/- 0.03 and gamma=1.25 +/- 0.05 are obtained by the Kouvel-Fisher method, and delta=4.79 +/- 0.01 is generated by the critical iso-thermal analysis. The obtained exponent beta is close to the prediction of the three-dimensional (3D) Heisenberg model, while gamma approaches that of the 3D-Ising model. Although the bromine doping has prominent effect on the transport behavior, the critical exponents are hardly changed. The obtained results indicate that the ferromagnetism is established through one-dimensional Cr-Se-Cr bonds. However, the nearest-neighbor magnetic interaction belonging to the 3D-Heisenberg model also contributes to the ferromagnetic exchange.