First-order phase transition in perovskites Pr0.67Sr0.33MnO3 – 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 Pr0.67Sr0.33MnO₃. 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 TC, 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 Pr0.67Sr0.33MnO₃. Furthermore, we show by the energy histogram taken at TC that the transition is clearly of first order. We also calculate the magnetic entropy change |Δ Sₘ| 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 Sₘ| and the values of RCP. This perovskite compound has a good potential in refrigeration application due to its high RCP.