Observation of enhanced magnetic entropy change near room temperature in Sr-site deficient La_0.67Sr_0.33MnO₃ manganite

Abstract

The effect of Sr-site deficiency on the structural, magnetic and magnetic entropy change of La0.67Sr0.33−yMnO3−δ (y = 0.18 and 0.27) compounds was investigated.

Expansion of the multifunctionality in off-stoichiometric manganites using post-annealing and high pressure: physical and electrochemical studies

“…Rare-earth perovskite manganites have been extensively studied in the past few decades owing to their easy chemical production and structural diversity, as well as colossal magnetoresistance and high magnetocaloric effect (MCE) near the Curie temperature T C . [1][2][3][4] All these have significantly increased interest in them and promoted the search for ways of their potential practical applications in magnetic memory devices, batteries, fuel cells, transistors, spintronic and electronic devices, magnetic refrigerators, medicine for treating cancer, and drug delivery. [5][6][7][8] The recent development of new magnetic refrigeration technology based on the MCE has become an alternative green and environmentally friendly approach compared to the conventional gas compression technique.…”

“…24 Cation vacancies V (c) in the A-sublattice sufficiently influence the magneto-transport properties of manganites modifying Mn-O bond lengths and Mn-O-Mn bond angles, which are responsible for the strength of exchange interactions, and for the appearance of Mn 2+ ions in the A-sites and an additional multiple FM DE interaction. 2,23,[25][26][27][28] In addition, a change in the content of Mn in the A-and Bsites by the substitution of other ions, creation of cation vacancies V (c) B or introduction of overstoichiometric manganese also strongly influences the magneto-transport properties of manganites. 2,23,25,26,[28][29][30][31][32] Introducing excess Mn in the A-and/ or B-positions has a number of advantages since it brings to the completeness of the B-sublattice due to the existence of V (c) B vacancies and significantly improves the magneto-resistance effect without lowering T C ; [33][34][35][36] increases the metal-insulator temperature; 28 enhances transport properties and the FM metallic state due to the appearance of Mn 2+ ions in the A-sites, which have a half-filled conduction band crossing the Fermi level, and causes the multiple DE.…”

“…2,23,[25][26][27][28] In addition, a change in the content of Mn in the A-and Bsites by the substitution of other ions, creation of cation vacancies V (c) B or introduction of overstoichiometric manganese also strongly influences the magneto-transport properties of manganites. 2,23,25,26,[28][29][30][31][32] Introducing excess Mn in the A-and/ or B-positions has a number of advantages since it brings to the completeness of the B-sublattice due to the existence of V (c) B vacancies and significantly improves the magneto-resistance effect without lowering T C ; [33][34][35][36] increases the metal-insulator temperature; 28 enhances transport properties and the FM metallic state due to the appearance of Mn 2+ ions in the A-sites, which have a half-filled conduction band crossing the Fermi level, and causes the multiple DE. 23 It also increases the T C and MCE, for example, in La 0.67 Ca 0.33 Mn 1+d O 3 nanopowders with ÀDS M = 2.94 J kg À1 K À1 (5 T) at T C = 240 K for d = 0 and ÀDS M = 2.90 J kg À1 K À1 (5 T) at T C = 248 K for d = 0.05; 37 in La 0.8Àx Ag 0.2 Mn 1+x O 3 bulk with ÀDS M = 2.40 J kg À1 K À1 (1 T) at T C = 300 K for x = 0, 38 and ÀDS M = 2.46 J kg À1 K À1 (1 T) at T C = 271 K for x = 0.1, 3 and in La 0.8Àx Ag 0.2 Mn 1+x O 3 nanopowders with ÀDS M = 0.96 J kg À1 K À1 (2 T) at T C = 306 K for x = 0, 39 and ÀDS M = 2.03 J kg À1 K À1 (1 T) at T C = 308 K for x = 0.2.…”

“…24 Cation vacancies V (c) in the A-sublattice sufficiently influence the magneto-transport properties of manganites modifying Mn–O bond lengths and Mn–O–Mn bond angles, which are responsible for the strength of exchange interactions, and for the appearance of Mn 2+ ions in the A-sites and an additional multiple FM DE interaction. 2,23,25–28…”

“…This work presents the results of a parallel study of the electrochemical properties of La 0.9 Mn 1.1 O 3 manganites along with investigating changes in crystallite sizes, structural features, and thermal properties, as well as their interconnection. For this purpose, off-stoichiometric La 0.9 Mn 1.1 O 3− δ ceramic samples have been selected and synthesized due to the following reasons: (i) high reproducibility of the samples, 3,32,38 (ii) Mn-containing perovskites are effective catalysts, 18 (iii) this off-stoichiometric compound 0.9 : 1.1 : 3− δ demonstrates the non-zero magnetization in contrast to the classical antiferromagnetic (AFM) one 1 : 1 : 3, 41 (iv) they have one of the most stable perovskite crystal structure with a tolerance factor t of 0.946 closed to 1, 42 (v) the presence of cation vacancies at A-positions leads to the appearance of an additional magnetism from Mn 2+ ions, 2,23,25–28 and (vi) the overstoichiometric manganese on B-sites improves the magneto-transport and magnetocaloric properties. 3,33–36,40 Thus, the structural, microstructural, magnetic, magnetocaloric, and electrochemical properties of La 0.9 Mn 1.1 O 3 ceramics depending on post-annealing and/or high hydrostatic pressure have been studied systematically.…”