Magnetic entropy table-like shape and enhancement of refrigerant capacity in La 1.4 Ca 1.6 Mn 2 O 7 -La 1.3 Eu 0.1 Ca 1.6 Mn 2 O 7 composite.

In this work, we have investigated the structural, magnetic and magnetocaloric properties of La 1.4 Ca 1.6 Mn 2 O 7 (A) and La 1.3 Eu 0.1 Ca 1.6 Mn 2 O 7 (B) oxides. These compounds are synthesized by a solid-state reaction route and indexed with respect to Sr 3 Ti 2 O 7 -type perovskite with the I 4/ mmm space group. The substitution of La by 10% Eu enhances the value of magnetization and reduces the Curie temperature ( T C ). It is also shown that these compounds undergo a first-order ferromagnetic-paramagnetic phase transition around their respective T C . The investigated samples show large magnetic entropy change (Δ S M ) produced by the sharp change of magnetization at their Curie temperatures. An asymmetric broadening of the maximum of Δ S M with increasing field is observed in both samples. This behaviour is due to the presence of metamagnetic transition. The Δ S M ( T ) is calculated for A x /B 1- x composites with 0 ≤ x ≤ 1. The optimum Δ S M ( T ) of the composite with x = 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 0.48 /B 0.52 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 S M ( T ) peaks. A table-like magnetocaloric effect is observed and the result is found to be in good agreement with the calculations. The obtained Δ S M ( T ) is ≈4.07 J kg -1 K -1 in a field change of 0-5 T in a wide temperature span over Δ T FWHM ∼ 68.17 K, resulting in a large refrigerant capacity value of ≈232.85 J kg -1 . The MCE in the A 0.48 /B 0.52 has demonstrated that the use of composite increases the efficiency of magnetic cooling with μ 0 H = 5 T by 23.16%. The large Δ T FWHM and RC values together with the table-like (-Δ S M ) max feature suggest that the A 0.48 /B 0.52 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 N presents a maximum of N > 2 for A, B and A 0.48 /B 0.52 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.