MAGNETIC PROPERTIES OF KMnF$sub 3$. I. CRYSTALLOGRAPHIC STUDIES

摘要: The lattice parameters for KMn${\mathrm{F}}_{3}$ have been determined by means of an x-ray rotation camera designed temperatures down to 15\ifmmode^\circ\else\textdegree\fi{}K. cubic room temperature perovskite structure transforms at 184\ifmmode^\circ\else\textdegree\fi{}K orthorhombic phase with ${{D}_{2h}}^{16}\ensuremath{-}Pbnm$ as the most probable space group a unit cell containing 4 formula units; it has tetragonal pseudocell $\frac{c}{a}g1$ in which fluorine octahedra about manganese remain essentially regular but till relative crystal axes. At 84\ifmmode^\circ\else\textdegree\fi{}K, just below N\'eel 88\ifmmode^\circ\else\textdegree\fi{}K, pure antiferromagnetic also pseudocell, $\frac{c}{a}l1$ and still rotated well twisted. Below second magnetic transition 81.5\ifmmode^\circ\else\textdegree\fi{}K, 65\ifmmode^\circ\else\textdegree\fi{}K shows addition significant distortion regularity octahedra.