Magnetic, thermal and ferroelectric properties of MOFs (MHyM, M = Fe, Mn) close to phase transitions

•Magnetic, thermal and ferroelectric properties of MOFs were studied.•Molecular field theory, Ising compressible model and the power-law formula were used.•The experimental data for MHyFe and MHyMn from the literature were analyzed.•Our calculated results describe the observed behaviour satisfactorily. Magnetic, thermal and ferroelectric properties of MOFs (metal organic frameworks), in particular, the compounds CH3NH2NH2M(HCOO)3 (MHyM) with M = Fe and Mn, are studied close to phase transitions. For the magnetic properties, the molecular field theory at low temperatures and the power-law formula within the framework of an Ising pseudospin-phonon coupled model close to TC are performed by using the observed magnetization data for MHyFe and MHyMn from the literature. For the thermal properties, particularly, the heat capacity CP, Ising compressible model with the power-law formula is introduced to analyze the experimental data by considering the two anomalies in CP at the critical temperatures (TC1and TC2) for MHyFe and MHyMn. Within these two anomalies, the ferroelectric properties of MHyMn are also studied by analyzing the observed data for the spontaneous polarization PS using the power-law formula. Our calculations show that the molecular field theory is satisfactory for the temperature dependence of the magnetization at low temperatures well below TC at constant fields, with the M(T) at 0.1 kOe close to TC in MHyFe. Values of the critical exponent β for the magnetization from our analysis using the power-law formula close to TC(=Tm), are acceptable for both compounds (MHyFe and MHyMn). Regarding the thermal properties, an Ising compressible model is adequate to describe the observed behaviour of the heat capacity CP with the two anomalies (TC1and TC2) for MHyFe and MHyMn. Also, for the ferroelectric properties of those compounds the temperature dependence of the spontaneous polarization PS at TC1and TC2 (MHyMn) is studied by the power-law formula from an Ising compressible model which describes the observed behaviour of PS in this compound.