Moscow State University, Moscow 119991, Russia.
J Phys Condens Matter. 2011 Jul 13;23(27):276003. doi: 10.1088/0953-8984/23/27/276003. Epub 2011 Jun 17.
A dynamic spin-fluctuation theory that directly takes into account nonlocality of thermal spin fluctuations and their mode-mode interactions is developed. The Gaussian approximation in the theory is improved by a self-consistent renormalization of the mean field and spin susceptibility due to the third-and fourth-order terms of the free energy, respectively. This eliminates the fictitious first-order phase transition, which is typical for the Gaussian approximation, and yields a proper second-order phase transition. The effect of nonlocal spin correlations is enhanced by taking into account uniform fluctuations in the single-site mean Green function. Explicit computational formulae for basic magnetic characteristics are obtained. The extended theory is applied to the calculation of magnetic properties of Fe-Ni Invar. Almost full agreement with experiment is achieved for the magnetization, Curie temperature, and local and effective magnetic moments.
我们发展了一种动态自旋涨落理论，该理论直接考虑了热自旋涨落的非局域性及其模式-模式相互作用。通过自由能的第三和第四阶项对平均场和自旋磁化率进行自洽重整化，改进了理论中的高斯近似。这消除了高斯近似中典型的虚假一级相变，并产生了适当的二级相变。通过考虑单站点平均格林函数中的均匀涨落，增强了非局域自旋相关性的影响。获得了基本磁性特征的显式计算式。扩展理论应用于 Fe-Ni Invar 的磁性计算。对于磁化强度、居里温度以及局域和有效磁矩，与实验几乎完全一致。
