Thermodynamic properties of mixed-spin chains in magnetic field by the transfer matrix method

Motivated by recent experimental synthesis of molecule-based ferrimagnetics, we have investigated the thermodynamic properties of one-dimensional antiferromagnetic-ferromagnetic mixed spin-12 lozenge chain in external magnetic fields at low temperature, using the transfer matrix method. The magnetization and the specific heat of the spin system have been evaluated numerically from the free energy. The magnetization as a function of the magnetic field at low temperature shows step-like plateau characterized by three critical magnetic fields, which reflects the competing effect of magnetic interactions and thermal fluctuations. The double-peak structure in the curves of the specific heat is also found, which comes from the huge variation of the long-range order parameters. Our results show that the thermodynamic properties of the mixed spin-12 molecule-based ferrimagnetics are very analogous to the behaviors of the spin-1 and spin-12 mixed antiferromagentic chain.