Calculation of the Magnetization and the Heat Capacity for [Nh2 Nh3][M(hcoo)3] (M=fe, Mn) Near the Phase Transitions

Abstract

Temperature dependence of the magnetization M(T) is calculated for [NH2 NH3][M(HCOO)(3)] (M=Fe, Mn), namely, HyFe (perovskite and chiral) below T m =12.5 K and, for HyMn (chiral) below and above T m =7.9 K (at 100 Oe) by the molecular field theory (MFT). Close to the magnetic transition temperature ( T m ), the temperature (at 100 Oe) and the field (at 2K) dependence of the magnetization M(T, H) is analyzed by the power-law formula using the literature data. Magnetic susceptibility is predicted as a function of the field (T = 2K). Also, the temperature dependence of the heat capacity is calculated by the compressible Ising model close to the structural phase transitions in perovskite ( T C =347 K) and chiral ( T C =336 K) HyFe and the chiral ( T C =296 K) HyMn. Our results indicate that HyM (M=Fe, Mn) exhibit weak first order or near second order transitions (magnetic transition and the structural phase transitions).