Large magnetocaloric effect in La0.75Ca0.25–xNaxMnO3 (0 ≤ x ≤ 0.10) manganites

Abstract

We have studied the effect of a partial substitution of Ca2+ by Na+ on the structural, magnetic and magnetocaloric properties of the mixed valence perovskites $${\text{La}}_{{{0}{\text{.75}}}} {\text{Ca}}_{{{0}{\text{.25 - }}x}} {\text{Na}}_{x} {\text{MnO}}_{{3}}$$ (0 ≤ x ≤ 0.10), prepared by the flux method. X-ray diffraction studies revealed that our samples crystallize in the orthorhombic structure with a Pbnm space group. Rietveld analysis showed that MnO6 octahedron has a little distortion and that θMn–O–Mn bond angles increase with increasing Na+ content. The field cooled (FC) and zero field cooled (ZFC) magnetizations indicated that our samples have a paramagnetic-ferromagnetic phase transition, when decreasing temperature. A small deviation was observed between FC and ZFC curves. This deviation can be explained by the competition between the ferromagnetic and antiferromagnetic interactions, leading to a glassy behavior. The Curie temperature, TC, increased from 268 K for x = 0 to 278 K for x = 0.10. The magnetizations isotherms of our compounds, with a second-order phase transition, were investigated. For the x = 0.10 sample, the maximum of the magnetic entropy change was found to be 3.15 and 6.44 J kg−1 K−1, under an applied magnetic field of 2 and 5 T, respectively. Moreover, it has important relative cooling power values of about 134.82 and 317.79 J kg−1, under the same applied magnetic field. In addition, rescaled entropy data collapsed into the same curve, which indicates the universal behavior for the magnetocaloric effect (MCE) in our compounds. These materials could be potential candidates as working substances in magnetic refrigeration.