Neutron-diffraction study of the magnetic structure of KFeCl3

The compound KFe${\mathrm{Cl}}_3$ is paramagnetic at room temperature and belongs to the space group $D_{2h}^{16}-\mathrm{Pnma}$ with four molecules per unit cell. A neutron-diffraction study of a powder sample of KFe${\mathrm{Cl}}_3$ was carried out as a function of the sample temperature. A transition to an antiferromagnetic state was found at $T_N\sim 16$ K. The magnetic structure, as determined from the diffraction pattern at 4.2 °K, consists of antiferromagnetically coupled ferromagnetic chains paralled to the $b$ axis. The antiferromagnetic axis is along $b$ and the magnetic moment per ${\mathrm{Fe}}^{2+}$ ion calculated from the 4.2 °K pattern is (4.1 ± 0.3)${\mathrm{\mu }}_{\mathit{B}}$. Susceptibility measurements, on the other hand, yielded an effective magnetic moment of (5.5 ± 0.1)${\mathrm{\mu }}_{\mathit{B}}$. A broad line which appears above $T_N$ is interpreted in terms of strong intrachain one-dimensional ferromagnetic correlations. It is argued that such behavior is reasonable in a compound having this type of crystallographic structure.