THE SPIN WAVE THEORY OF A HEISENBERG FERROMAGNETIC SYSTEM WITH BIQUADRATIC EXCHANGE INTERACTION AT LOW TEMPERATURES
具有四次幂交换作用的Heisenberg铁磁体的低温自旋波理论

We presented here a theory of the Heisenberg ferromagnetic system with biquadratic exchange interaction at, low temperatures. In our theory, the kinematic and dynamic interactions are correctly included. The expansion for Sz in terms of temperature and the temperature dependence of spin wave spectrum are obtained ri-grously.