Magnetic interactions in CoBr2·6H2O

High-precision measurements of the heat capacity of CoBr2·6H2O 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 XY antiferromagnet yielded Jk=-2.5 K. A combination with antiferromagnetic-resonance results gave J1xx=-2.4 K, J1yy=-2.3 K, J1zz=-0.3 K for the intersublattice interaction and J2xx=-0.5 K, J2yy=-0.5 K, and J2zz=-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 (β=0.31), a somewhat bidimensional character could be concluded. The effect of deuteration will be briefly considered.