title: A giant magnetocaloric effect with a tunable temperature transition close to room temperature in Na-deficient La0.8Na0.2-x□xMnO3 manganites.
abstract: A giant magnetocaloric effect induced by sodium-deficiency in a La0.8Na0.2-x□xMnO3 (0.00 ≤ x ≤ 0.15) polycrystalline sample is reported in the present research work. The ability to tune the temperature transition close to room temperature is revealed to be possible by changing the sodium-deficiency content as well. All samples were synthesized using solid-solid reaction. X-ray diffraction and magnetization measurements were performed to investigate their crystallographic structure and magnetocaloric properties. A rhombohedral structure with the R3[combining macron]c space group is deduced from pattern diffraction refinement of all samples. A second-order magnetic phase transition from the ferromagnetic to the paramagnetic state at the Curie temperature (Tc) is observed. Such a Tc decreased from 335 to 260 K when the sodium deficiency rate increased. Besides, the magnetic entropy change and the related Relative Cooling Power (RCP) values, sensitive to sodium-deficiency, were estimated. The magnetic entropy change ranges increased from 2.38 J kg(-1) K(-1) to 3.48 J kg(-1) K(-1) under a magnetic field of 2 T, whereas the RCP varied from 210 to 235 J kg(-1) under an applied magnetic field of 5 T, when x increased from 0.00 to 0.15. The comparison of the values reported in the reference Gd material underlines that the proposed oxide material has substantial advantages for magnetic refrigeration.
authors.affiliation: Laboratoire de Physique Appliquée, Faculté des Sciences de Sfax, B.P. 802, Université de Sfax, Sfax 3018, Tunisia. mouna.wali@yahoo.fr.
authors.forename: M
authors.initials: M
authors.lastname: Wali
authors.forename: R
authors.initials: R
authors.lastname: Skini
authors.forename: M
authors.initials: M
authors.lastname: Khlifi
authors.forename: E
authors.initials: E
authors.lastname: Dhahri
authors.forename: E K
authors.initials: EK
authors.lastname: Hlil