First-Order Phase Transition in Perovskites Pr_0.67Sr_0.33MnO_3 - Magneto-Caloric Properties – Effect of Multi-Spin Interaction

We show by extensive Monte Carlo simulations that we need a multi-spin interaction in addition to pairwise interactions in order to reproduce the temperature dependence of the experimental magnetization observed in the perovskite compound Pr_0.67Sr_0.33MnO_3. The multi-spin interaction is introduced in the Hamiltonian as follows: each spin interacts simultaneously with its four nearest-neighbors. It does not have the reversal invariance as in a pairwise interaction where reversing the directions of two spins leaves the interaction energy invariant. As a consequence, it competes with the pairwise interactions between magnetic ions. The multi-spin interaction allows the sample magnetization M to increase, to decrease or to have a plateau with increasing T. In this paper we show that M increases with increasing T before making a vertical fall at the transition temperature T_C, in contrast to the usual decrease of M with increasing T in most of magnetic systems. This result is in an excellent agreement with the experimental data observed in Pr_0.67Sr_0.33MnO_3. Furthermore, we show by the energy histogram taken at T_C that the transition is clearly of first order. We also calculate the magnetic entropy change |Δ S_m| and the Relative Cooling Power (RCP) by using the set of curves of M obtained under an applied magnetic field H varying from 0 to 5 Tesla across the transition temperature region. We obtain a good agreement with experiments on |Δ S_m| and the values of RCP. This perovskite compound has a good potential in refrigeration application due to its high RCP.