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 T-c = 8 K. For AceMn, this analysis is performed using M/H-(X'ac) and M(H) near T-c = 9 K. The observed data from the literature are used for the power-law analysis. The critical exponents beta, delta, and gamma 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 gamma and delta 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.