On the determination of the magnetocaloric effect in the (La0.55Bi0.15)Ca0.3MnO3 perovskite

We have studied the magnetocaloric effect of the (La0.55Bi0.15)Ca0.3MnO3 perovskite. This material shows interesting magnetic properties, as its saturation magnetic moment per formula unit of 3.44 mu(B) and a magnetic order temperature of 230 K. Below this temperature neutron diffraction experiments show antiferromagnetic contributions in the main ferromagnetic structure. The measured heat capacity exhibits a broad jump centred at the Curie temperature. By increasing the magnetic field, the jump shifts to higher temperatures, confirming the ferromagnetic character of the transition. From the total entropy we have determined the isothermal magnetic entropy (Delta S-m) and the adiabatic temperature change (Delta T-ad). We found that both magnitudes display peaks centred at 230 K with maximum values of vertical bar Delta S-m vertical bar= 1.1 J/K.mol and Delta T-ad = 2.3 K at 9 T applied field. Although these values are modest, it is significant that the magnetocaloric effect extends over a large temperature range. Isothermal measurements of magnetization allow us, through thermodynamic Maxwell relation, to determine the isothermal magnetic entropy. The temperature dependences of Delta S are similar to those obtained from Cp although the values are slightly higher.