Magnetic Structure of NaNiF3

Abstract

The structure of NaNi${\mathrm{F}}_3$ has orthorhombic symmetry ($Pbnm-{D_{2h}}^{16}$). It is found, using neutron diffraction, that it undergoes a magnetic transition at $T_n\simeq 149°$K to an antiferromagnetic mode of the type $G_x$. This mode belongs to the magnetic space group $P{b}^{\prime }{n}^{\prime }m$ which allows ferromagnetism in the $z$ direction. Weak ferromagnetism in this direction was indeed found in previous experiments. This result is in contrast to a recent suggestion made by Judin and Sherman. It is nevertheless in accord with what one expects and finds in structures of this type (orthoferrities, for example). On the basis of the present data it is suggested that it is probably the antisymmetric exchange interaction which is responsible for the weak ferromagnetism in this compound.