A giant magnetocaloric effect with a tunable temperature transition close to room temperature in Na-deficient La_0.8Na_0.2−x□_xMnO₃manganites

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.

Study of magnetic and electrical properties of Pr0.65Ca0.25Ba0.1MnO3manganite

“…Thus, the resulting RCP values are found to be 104.2 and 263.5 J kg À1 under a magnetic eld changes of 2 and 5 T, respectively. The obtained values are comparable with those of several manganite systems with a large MCE, [26][27][28][29][30][31][32] suggesting that our compound may be suitable candidate for magnetic refrigeration. The large MCE in Pr 0.65 -Ca 0.25 Ba 0.1 MnO 3 can be understood by its sharp magnetization change at the FM-PM transition and its high magnetization saturation.…”

Impact of Annealing Temperature on the Physical Properties of the Lanthanum Deficiency Manganites

“…However, Zhang et al [21] observed that Tc decreased with increase in the grain size in the range of 24.4-240 nm. It is known that this variation of Tc is controlled by the electron bandwidth W and the mobility of eg electrons [11,22,23]. In fact, the structure, magnetism, and the magnetocaloric effect are very correlated, primarily by the bandwidth W.…”

Distribution of Transition Temperatures in Magnetic Transformations: Sources, Effects and Procedures to Extract Information from Experimental Data

“…transition temperature as a function of the Mn +4 fraction in La-manganites (data taken from supplemental material of [29] and [31][32][33][34][35][36][37]). [29] and [31][32][33][34][35][36][37]).…”