Thermal and Magnetic Study of CoBr₂·6H₂O

Abstract

The measurements of specific heats, isentropic curves and isothermal susceptibilities under an external field are carried out for single crystals of CoBr₂·6H₂O. 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 J₁ and J₂ are estimated as 1.75k_B and 1.13k_B respectively. The other path of exchange interaction J₃ along the c axis, is determined as 0.57k_B. The critical exponents of specific heat near the Néel point are shown as α=0.6±0.1 and α′=−0.1±0.1 at zero magnetic field.