磁性晶体二级相变理论与镧系金属的磁结构

本文讨论了Ландау二级相变理论中的稳定性条件,阐明了Лифшиц提出的对称改变限制条件是不必要的,从而可以讨论过去认为无法讨论的镧系金属镝(Dy)等在Neél点的二级相变,解释了镧系金属镝等在Neél点以下螺旋磁结构的螺距与温度成线性关系。同时,利用空间羣表示论和热力势极小条件,建立了一个讨论磁结构的新方法,用这方法分析了镧系金属的磁结构,所得的结果与中子衍射实验相符合。

SECOND ORDER PHASE TRANSFORMATION OF MAGNETIC CRYSTALS AND MAGNETIC STRUCTURE OF METALS OF THE LANTHANUM SERIES

The stability conditions in the Landau theory of second order phase transformation are discussed. It is shown that the restrictions imposed by Lifshitz on the change of type of symmetry are not necessary. As a consequence, the second order transformation at the Neél point of metals of the Lanthanum series such as dysprosium, which was thus far regarded as a problem that could not be treated on the basis of the Landau theory, is amenable to theoretical treatment. The linear relationship to temperature of the pitch of the helical spin structure of dysprosium is explained. In the meantime, a new method for the analysis of spin structure is developed employing the theory of space group representation and the minimum conditions of the thermodynamic potential. The results obtained by the application of this method to the magnetic structure of metals of the Lanthanum series are in agreement with the results of neutron diffraction experiments.