Effects of exchange interaction and spin-fluctuation on the magnetic and magneto-optic properties of NdF₃

The exchange interaction between the electrons in the different magnetic ions and the spin-fluctuation of the magnetic ions exist in the paramagnetic media NdF_3. The exchange interaction between the electrons in the different magnetic ions may be equivalent to an effective field H_in that is in direct proportion to the magnetization M. The spin-fluctuation of the magnetic ions leads the coefficient of the effective field to vary with temperature. The effective field is given as H_\rm in = - (0.75 + 0.22\rm T) \times 10^^ - 5M in NdF_3. When the secondary crystal field effect is taken into account, the magnetic susceptibility and Verdet constant are calculated for NdF_3 by means of the effective field H_\rm in and the applied field H_e. The calculated results are in agreement with the measured ones.