Magnetic entropy table-like shape and enhancement of refrigerant capacity in La1.4Ca1.6Mn2O7-La1.3Eu0.1Ca1.6Mn2O7 composite

R M'nassri; Muaffaq M Nofal; P de Rango; N Chniba-Boudjada

doi:10.1039/c9ra00984a

Magnetic entropy table-like shape and enhancement of refrigerant capacity in La_1.4Ca_1.6Mn₂O₇-La_1.3Eu_0.1Ca_1.6Mn₂O₇ composite

RSC Adv. 2019 May 14;9(26):14916-14927. doi: 10.1039/c9ra00984a. eCollection 2019 May 9.

Authors

R M'nassri¹, Muaffaq M Nofal², P de Rango³, N Chniba-Boudjada³

Affiliations

¹ Unité de recherche Matériaux Avancés et Nanotechnologies (URMAN), Institut Supérieur des Sciences Appliquées et de Technologie de Kasserine, Kairouan University BP 471 Kasserine 1200 Tunisia rafik_mnassri@yahoo.fr.
² Department of Mathematics and General Sciences, Prince Sultan University P. O. Box 66833 Riyadh 11586 Saudi Arabia.
³ Institut NEEL BP 166 38042 Grenoble Cedex 09 France.

Abstract

In this work, we have investigated the structural, magnetic and magnetocaloric properties of La_1.4Ca_1.6Mn₂O₇ (A) and La_1.3Eu_0.1Ca_1.6Mn₂O₇ (B) oxides. These compounds are synthesized by a solid-state reaction route and indexed with respect to Sr₃Ti₂O₇-type perovskite with the I4/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 (ΔS _M) produced by the sharp change of magnetization at their Curie temperatures. An asymmetric broadening of the maximum of ΔS _M with increasing field is observed in both samples. This behaviour is due to the presence of metamagnetic transition. The ΔS _M(T) is calculated for A _x /B_1-x composites with 0 ≤ x ≤ 1. The optimum ΔS _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 ΔS _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 ΔS _M(T) is ≈4.07 J kg^-1 K^-1 in a field change of 0-5 T in a wide temperature span over ΔT _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 ΔT _FWHM and RC values together with the table-like (-ΔS _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.