Magnetic Structure of the Two-Dimensional Antiferromagnet BaCoF4

Abstract

The results of magnetic-susceptibility and neutron-diffraction measurements on BaCo${\mathrm{F}}_4$ show behavior characteristic of a two-dimensional antiferromagnet. The material is highly anisotropic and exhibits two magnetic phases, $A$ and $B$, both of which order in three dimensions at the same temperature, $T_N=(69.6\mathrm{}\pm 0.1)°$K. The magnetic structure consists of puckered (010) layers of moments within which nearest neighbors are coupled antiparallel. The ordering of the moments 14 Å apart in the $b$ direction is antiparallel in phase $A$ and parallel in phase $B$. The moments are directed along [100]. If the ${\mathrm{Co}}^{2+}$ moment is assumed to be the same for both phases, then the ordered moments have a magnitude of $(3.4\mathrm{}\pm 0.2){\mu }_B$ at 4.7 °K.