Thermal and Magnetic Study of CoBr2·6H2O

The measurements of specific heats, isentropic curves and isothermal susceptibilities under an external field are carried out for single crystals of CoBr 2 ·6H 2 O. The hysteresis is observed at the phase boundary between antiferromagnetic (AF) and spin-flopping (SF) states. The molecular field constants are calculated from the magnetic specific heat and the magnetic phase diagram. The two kinds of path in exchange interaction at the ab plane, so called J 1 and J 2 are estimated as 1.75 k B and 1.13 k B respectively. The other path of exchange interaction J 3 along the c axis, is determined as 0.57 k B . The critical exponents of specific heat near the Neel point are shown as α=0.6±0.1 and α'=-0.1±0.1 at zero magnetic field.