Phase transition and magneto-caloric properties of perovskites Pr0.55Sr0.45MnO3: Modeling versus experiments

Experimental data obtained with the perovskite compounds Pr0.55Sr0.45MnO3 show that the magnetization decreases with increasing temperature T and undergoes a very sharp phase transition to the paramagnetic phase. The sharp transition in a system with a strong disorder is very rare, if not non-existent, in the theory of phase transition in systems of short-range pairwise exchange interactions. To understand this remarkable property, we introduce a model including a multispin (cluster-like) interaction between Mn ions, in addition to the usual pairwise exchange terms between these ions and the Mn–Pr interactions. We carry out Monte Carlo (MC) simulations using this model. The crystal is a body-centered tetragonal lattice where the corner sites are occupied by Mn ions and the center sites by Pr or Sr ions. Due to the doping, Mn4+ with S=3/2 has the concentration of Pr3+ (S=1) and Mn3+ with S=2 has the Sr concentration. After attempts with different spin models and various Hamiltonians, we find that the many-state Ising spin model reproduces most of the experimental results. For the Hamiltonian, we find that pairwise interactions alone between ions cannot reproduce the sharp transition and the magnetization below TC. We have to include a multispin interaction as said above. We fit the MC results with experimental data, and we estimate values of various exchange interactions in the system. These values are found to be in the range of those found in perovskite manganite compounds. We also study the applied-field effect on the magnetization in the temperature region below and above the transition temperature TC. We calculate the magnetic entropy change |ΔSm| and the Relative Cooling Power, for magnetic field from 1 to 3 T. Our simulation results are in good agreement with experiments. The role of the multispin interaction is analyzed and discussed.