磁原胞与化学原胞不一致的磁性晶体的磁结构

本文发展了一个讨论磁原胞与化学原胞不一致的磁性晶体的自旋位形的宏观方法。引进一个有限羣,其元素乃是分布于一个磁原胞内的空间羣的元素。该羣的对称元素作用于次晶格的自旋密度上,使热力势保持不变。利用这原理可以建立热力势按次晶格自旋密度的展式。由热力势取极小条件决定磁性晶体的自旋位形。应用这个方法具体地讨论了四类磁性晶体的自旋位形,对每一类情况得到了与中子衍射实验一致的结果。利用本方法在某些情况下,也可以得到螺旋形的自旋位形。

THE MAGNETIC STRUCTURES OF CRYSTALS WITH MAGNETIC UNIT CELL UN-IDENTICAL WITH ITS CHEMICAL UNIT CELL

In this work a phenomenological method is developed for the determination of spin configurations of magnetic crystals with a magnetic unit cell un-identical with its chemical unit cell. A finite group, formed of those elements of the space group which are distributed within a magnetic unit cell, is introduced. The expansion of the thermo-dynamic potential in terms of sublattice spin densities is constructed according to the principle that it should be invariant when symmetry operations of the above mentioned group are applied on sublattice spin densities separately. Spin configurations of magnetic crystals are then determined from the minimum condition of thermodynamic potential.With the above method, we have discussed the spin configurations of magnetic crystals of four different types. In each case, the results obtained are consistent with those of neutron diffraction experiments. Under certain conditions the existence of helical spin configuration may also be accounted for with the aid of this method.