自发磁化交换偏置的朗道相变理论

为了研究具有自发磁化交换偏置不对称性材料的自由能密度F的特征,采用朗道的相变理论,处理自发磁化的交换偏置不对称性.一维情况下对称性的自由能密度F展开成自发磁化强度M(T)的偶次幂级数,而不对称的自由能密度F只要考虑M3(T)项,这样,在铁磁一顺磁相变温度Tc附近,得到了具有二级相变特征的不对称的M-T和(F-g0)-M曲线.其中,F的幂级数展开系数的定性关系为:g2=γ(T-Tc);g3随T的减小非线性减小;g4随T的减小而增大.

Landau Theory of Phase Transition Applied to Bias Exchange of Spontaneous Magnetization

In order to study the character of free energy density F of some material with an asymmetry of bias exchange of spontaneous magnetization, Landau theory of phase transition is adopted to study the asymmetry. Symmetric free energy density F in one-dimension is expanded into the even power series of spontaneous magnetisation intensity M( T). As for asymmetric F, only M3(T) term is put into consideration, thus the asymmetric M-T and ( F-go )-M curves with the character of second-order phase transition are obtained near the transition temperature Tc between the ferromagnetic and paramagnetic states. The qualitative relation of expansion coefficient of the power series of F is: g2 = γ ( T- Tc ), in which g3 decreases and g4 increases in nonlinearity with the decrease of temperature.