Magnetic entropy table-like shape and enhancement of refrigerant capacity in LaCaMnO-LaEuCaMnO composite.

In this work, we have investigated the structural, magnetic and magnetocaloric properties of LaCaMnO (A) and LaEuCaMnO (B) oxides. These compounds are synthesized by a solid-state reaction route and indexed with respect to SrTiO-type perovskite with the 4/ space group. The substitution of La by 10% Eu enhances the value of magnetization and reduces the Curie temperature ( ). It is also shown that these compounds undergo a first-order ferromagnetic-paramagnetic phase transition around their respective . The investigated samples show large magnetic entropy change (Δ ) produced by the sharp change of magnetization at their Curie temperatures. An asymmetric broadening of the maximum of Δ with increasing field is observed in both samples. This behaviour is due to the presence of metamagnetic transition. The Δ () is calculated for A /B composites with 0 ≤ ≤ 1. The optimum Δ () of the composite with = 0.48 approaches a nearly constant value showing a table-like behaviour under 5 T. To test these calculations experimentally, the composite with nominal composition A/B is prepared by mixing both individual samples A and B. Magnetic measurements show that the composite exhibits two successive magnetic transitions and possesses a large MCE characterized by two Δ () peaks. A table-like magnetocaloric effect is observed and the result is found to be in good agreement with the calculations. The obtained Δ () is ≈4.07 J kg K in a field change of 0-5 T in a wide temperature span over Δ ∼ 68.17 K, resulting in a large refrigerant capacity value of ≈232.85 J kg. The MCE in the A/B has demonstrated that the use of composite increases the efficiency of magnetic cooling with = 5 T by 23.16%. The large Δ and RC values together with the table-like (-Δ ) feature suggest that the A/B composite can meet the requirements of several magnetic cooling composites based on the Ericsson-cycle. In addition, we show that the magnetic field dependence of MCE enables a clear analysis of the order of phase transition. The exponent presents a maximum of > 2 for A, B and A/B samples confirming a first-order paramagnetic-ferromagnetic transition according to the quantitative criterion. The negative slope observed in the Arrott plots of the three compounds corroborates this criterion.