Magnetic Structure of CoCs3Cl5and CoCs3Br5

The Luttinger-Tisza method has been used to calculate the low-temperature spin configurations of Co ions in Co${\mathrm{Cs}}_3$ ${\mathrm{Cl}}_5$ and Co${\mathrm{Cs}}_3$ ${\mathrm{Br}}_5$ crystals. In order to explain the purely antiferromagnetic arrangement of spins in Co${\mathrm{Cs}}_3$ ${\mathrm{Cl}}_5$, determined experimentally by Hammann from neutron diffraction, it is found that $J_4$ the fourth-nearest-neighbor exchange-interaction constant must be greater than 0.0086 K. For Co${\mathrm{Cs}}_3$ ${\mathrm{Br}}_5$, for which no detailed spin structure is available, it is found that the experimentally observed antiferromagnetic ordering of Co spins is most probably one of the layered-antiferromagnetic type.