Antiferromagnetic Properties of the Iron Group Trifluorides

A neutron diffraction study has been made of the trifluorides of $3d$ transition group elements. The arrangement of the magnetic ions and the anions in these trifluorides is similar to that in the compounds $\mathrm{La}M{\mathrm{O}}_{3}$ for which the antiferromagnetic properties have been studied earlier. No antiferromagnetic transition was observed in V${\mathrm{F}}_{3}$. In the compounds Cr${\mathrm{F}}_{3}$, Fe${\mathrm{F}}_{3}$, and Co${\mathrm{F}}_{3}$ the magnetic ions are observed to couple antiferromagnetically via the intervening anion to each of their six nearest neighbors. This is the same structure as that found in the compounds LaCr${\mathrm{O}}_{3}$ and LaFe${\mathrm{O}}_{3}$. In the trifluorides the distortions from cubic symmetry have made it possible to determine the orientation of the spin moments relative to the crystallographic axes and in one case (Cr${\mathrm{F}}_{3}$) the antiferromagnetic domain properties have been studied with magnetic fields applied to the sample. In Mn${\mathrm{F}}_{3}$ an antiferromagnetic layer structure is found of the type previously observed for LaMn${\mathrm{O}}_{3}$. The indirect magnetic coupling in these compounds is correlated with the orbitals which result from the splitting of the $d$ levels by the crystalline field.