Magnetic interactions in CoBr2·6H2O

Abstract

High-precision measurements of the heat capacity of Co${\mathrm{Br}}_{2}$\ifmmode\cdot\else\textperiodcentered\fi{}6${\mathrm{H}}_{2}$O were performed between 1.2 and 11 K. A fit of the high-temperature magnetic specific heat to the high-temperature-series expansion for a two-dimensional $\mathrm{XY}$ antiferromagnet yielded $\frac{J}{k}=\ensuremath{-}2.5$ K. A combination with antiferromagnetic-resonance results gave ${J}_{1xx}=\ensuremath{-}2.4$ K, ${J}_{1yy}=\ensuremath{-}2.3$ K, ${J}_{1zz}=\ensuremath{-}0.3$ K for the intersublattice interaction and ${J}_{2xx}=\ensuremath{-}0.5$ K, ${J}_{2yy}=\ensuremath{-}0.5$ K, and ${J}_{2zz}=\ensuremath{-}0.07$ K for the intrasublattice interaction. A calculation of the Curie constant, the perpendicular susceptibility, and the paramagnetic phase transition based upon these values gave satisfactory agreement with the experimental data. From the critical entropy (57%), as well as the critical behavior of the sublattice magnetization ($\ensuremath{\beta}=0.31$), a somewhat bidimensional character could be concluded. The effect of deuteration will be briefly considered.