Evidence for Antiferromagnetism in CoBr2·6H2O

An antiferromagnetic-paramagnetic transition has been observed in a single crystal of Co${\mathrm{Br}}_2$·6${\mathrm{H}}_2$O by by using the proton resonance technique and by measuring the heat capacity in the temperature range 1.65-5.05°K. The Néel temperature, obtained by the magnetic measurement is 3.08°K while the heat capacity measurement gave 3.07°K. The entropy change associated with the transition was calculated from the heat capacity data and yielded 1.42 cal/mole deg. The contribution to the entropy change above the Néel temperature was approximately 38% of the total entropy change, which indicates a rather slow diminution of the short-range ordering of the ${\mathrm{Co}}^{++}$ spins.