Adiabatic Magnetization Process in CoCl₂·2H₂O

Abstract

The entropy of a model Ising spin system for CoCl₂·2H₂O, which consisted of 24 spins with periodic boundary conditions in two-dimensional lattice, was calculated. The cooling effect was predicted at both fields H_c1 and H_c2 in adiabatic magnetization process.
The experiment of adiabatic magnetization on CoCl₂·2H₂O revealed that it was really the case. Bellow 5.9 K, however, temperature variation near both H_c1 and H_c2 was not simple; heating-up was observed after passing temperature minimum. These anomalies might be attributed to the hysteresis effect of spin arrangement among the excited levels as well as ground levels.