Evidence for Antiferromagnetism in CoBr2·6H2O

Abstract

An antiferromagnetic-paramagnetic transition has been observed in a single crystal of Co${\mathrm{Br}}_{2}$\ifmmode\cdot\else\textperiodcentered\fi{}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\ifmmode^\circ\else\textdegree\fi{}K. The N\'eel temperature, obtained by the magnetic measurement is 3.08\ifmmode^\circ\else\textdegree\fi{}K while the heat capacity measurement gave 3.07\ifmmode^\circ\else\textdegree\fi{}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 N\'eel 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.