Temperature and field dependences of the magnetization and the magnetic susceptibility in perovskite structures (FMDMn and AceMn)

Ferromagnetic properties of the perovskite structures, namely, [NH2–CH+–NH2] [Mn(HCOO)3] (FMDMn) and [CH3C(NH2)2] [Mn(HCOO)3] (AceMn), are studied close to magnetic phase transitions. Magnetization M(T) is calculated by the extended mean field model, and M(H) is analyzed for FMDMn near Tc = 8 K. For AceMn, this analysis is performed using M/H(χac′) and M(H) near Tc = 9 K. The observed data from the literature are used for the power-law analysis. The critical exponents β, δ, and γ for M(T), M/H, and M(H), respectively, are determined, which are compared with the expected values from the mean field theory, Ising and Heisenberg models. We find that the Landau mean-field model satisfactorily describes the magnetic behavior of M(T) values for the perovskite FMDMn. Our γ and δ values are not in agreement with those expected ones. It is indicated that both compounds (FMDMn and AceMn) exhibit weak first-order (or nearly second-order) behavior; in particular, a tricritical magnetic transition is suggested for FMDMn.