Role of lanthanum vacancy on the structural, magnetic and magnetocaloric properties in the lacunar perovskite manganites La0.8−x□xNa0.2MnO3 (0 ≤ x ≤ 0.15). Issue 79 (27th October 2017)

• Record Type: Journal Article
• Authors: Choura-Maatar, S.; M'nassri, R.; Cheikhrouhou-Koubaa, W.; Koubaa, M.; Cheikhrouhou, A.; Hlil, E. K.
• Is Part Of: RSC advances. Volume 7:Issue 79(2017)
• Page Start: 50347
• Page End: 50357
• Publication Date: 2017-10-27
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c7ra08610e
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : Lacunar La0.8− x □ x Na0.2 MnO3 (0 ≤ x ≤ 0.15) ceramics where □ is a lanthanum deficiency were synthesized via a sol–gel method. Abstract : Lacunar La0.8− x □ x Na0.2 MnO3 (0 ≤ x ≤ 0.15) ceramics where □ is a lanthanum deficiency were synthesized via a sol–gel method. Magnetic phase transitions and magnetocaloric effects of the ceramics have been systematically studied. Structural studies using X-ray diffraction show that all compounds crystallize in the rhombohedral structure with an R 3̄ c space group. The lanthanum deficiency does not modify the crystal structure of the pristine compound ( x = 0) but results in a slight change of the lattice parameters. The unit cell volume and Mn–O–Mn angle decrease with increasing deficiency content whereas the Mn–O bond length increases. This situation weakens the double-exchange interaction and hence reduces the Curie temperature ( T C ). By analyzing the temperature and field dependence of magnetization, we find that the La0.8− x □ x Na0.2 MnO3 family exhibits a second order magnetic phase transition whose critical temperature is tunable near room temperature. A considerable magnetic entropy change is observed in La0.8− x □ x Na0.2 MnO3 near room temperature. The maximum value of the relative cooling power (RCP) is found to be ∼268 J kg −1 in La0.65 □0.15 Na0.2 MnO3 at 5 T. This value of RCP is about ∼65.3% of that obtained in gadolinium metal, known as one of the most important materials for magnetic refrigeration, at the same magnetic field change of 5 T. With increasing vacancy our manganites exhibit a stable magnetocaloric effect in a wide temperature range. The results suggest that La0.8− x □ x Na0.2 MnO3 and its composite materials could be expected to have effective applications for magnetic refrigeration near room temperature.