Anisotropic Heisenberg spin system with biquadratic exchange interaction

Abstract

For anisotropic Heisenberg ferromagnet of S = 1 with the bilinear exchange interaction J and the biquadratic exchange interaction J 1, the magnetization 〈 S z 〉, the Curie temperature T c and the magnetic susceptibility χ have been calculated by making use of the pair model approximation. It is pointed out that the biquadratic exchange interaction J 1 gives different effects on the magnetization 〈 S z 〉 of the Heisenberg ferromagnet and the Ising ferromagnet especially in the negative region of J 1. Furthermore, it turns out that the Curie temperature for all anisotropic Heisenberg ferromagnets has nearly constant value for the biquadratic exchange interaction of J 1 = −J 10 .