Magnetic Properties of Jahn-Teller Distorted Cu-Ferrite Films

The crystal structure of copper iron oxide (CuFe2O4:Cu-ferrite) is transformed from cubic spinel to tetragonal symmetry by the Jahn-Teller (J-T) distortion. The degree of J-T distortion σ is theoretically given by the function σ=σ0 tanh (|A|σ/RBT), where σ0 is the degree of the distortion at 0 K, A is the energy term involved in the distortion, RB is Boltzmann's constant, and T is the absolute temperature. The films were prepared by vacuum evaporation and solid reaction, and their crystal structure, magnetic coercive force, and initial magnetization energy were investigated. The temperature dependence of the shift of the Bragg angle Δ2θ for XRD, the coercive force Hc, and the initial magnetization energy Ei were well fitted to the function C tanh (α/T−β), where C, α, and β are constants determined by experiment. Consequently, the interaction between the distortion and magnetic properties of Cu-ferrite films was considered to be caused by J-T distortion, and experimental results agreed with the theorem of J-T distortion.