Effect of Exchange Interaction on the Low-Temperature Ordering of Gadolinium Trichloride Hexahydrate

The low-temperature ordered state of ${\mathrm{Gd}}^{+++}$ ions in gadolinium trichloride hexahydrate (Gd${\mathrm{Cl}}_3$·6${\mathrm{H}}_2$O) lattice is investigated taking into account both the dipole-dipole and exchange interactions. It is found that while consideration of the dipole-dipole interaction alone predicts a ferromagnetic low-temperature ordered state, the inclusion of the exchange interaction predicts an antiferromagnetic low-temperature ordered state in agreement with the experimental observations.