The crystallographic and magnetic structure of both RbFe${\mathrm{Cl}}_3$·2${\mathrm{D}}_2$O and CsFe${\mathrm{Cl}}_3$·2${\mathrm{D}}_2$O have been determined from elastic-neutron-scattering experiments and nuclear magnetic resonance. Both compounds are orthorombic space group $\mathrm{Pcca}$, with lattice constants, at $T=4.2\mathrm{}$ K, $a=8.8760\mathrm{}\left(6\right)\mathrm{}$ Å, $b=6.8724\mathrm{}\left(4\right)\mathrm{}$ Å, $c=11.1807\mathrm{}\left(12\right)\mathrm{}$ Å for RbFe${\mathrm{Cl}}_3$·2${\mathrm{D}}_2$O and $a=8.9466\mathrm{}\left(6\right)\mathrm{}$ Å, $b=7.1247\mathrm{}\left(4\right)\mathrm{}$ Å, $c=11.3248\mathrm{}\left(10\right)\mathrm{}$ Å for CsFe${\mathrm{Cl}}_3$·2${\mathrm{D}}_2$O. The magnetic array below the ordering temperature can be described by a compensated four-sublattice system. The apparent chains in the structure posses a ferromagnetic moment in the $c$ direction, giving rise to metamagnetic phase transitions at relatively low field strengths.

• Received 14 February 1978

DOI:https://doi.org/10.1103/PhysRevB.18.2179