Effect of oxygen content on structural, magnetic and magnetocaloric properties of (La0.7Pr0.3)0.8Sr0.2Mn0.9Co0.1O3±δ

• Published in: Journal of magnetism and magnetic materials Vol. 476; pp. 199 - 206
• Main Authors: Mitrofanov, V.Ya, Estemirova, S.Kh, Kozhina, G.A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15-04-2019; Elsevier BV
• Subjects: Ferromagnetism; Heisenberg theory; Magnetic materials; Magnetic measurement; Magnetic measurements; Magnetic properties; Magnetic transitions; Magnetocaloric effect; Orthorhombic phase; Oxide materials; Oxygen; Oxygen content; Phase transitions; Refrigeration; Statistical models; Stoichiometry; Temperature; Three dimensional models; Transition temperature; X-ray diffraction; X-ray diffraction; Magnetic measurements; Magnetocaloric effect; Oxide materials; Phase transitions
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2018.12.097

•Increasing the oxygen content lowers the temperature of polymorphic phase transitions.•Oxygen non-stoichiometry has little effect on TC and MCE.•All the compositions have high values of |SMmax| and RCP.•The FM-PM transition broadens and shifts to higher T with increasing magnetic field.•The critical exponents matched well with the isotropic short range 3D-Heisenberg model.
The present study reports the effect of oxygen content on the structural, magnetic and magnetocaloric properties in the (La0.7Pr0.3)0.8Sr0.2Mn0.9Co0.1O3±δ (δ = +0.02, +0.01, −0.03) in the temperature range of 5–723 К. It has been found that the temperatures of structural phase transitions vary significantly depending on the oxygen index value, δ. In oxygen-deficient samples (δ = −0.03), two structural phase transitions are observed: O′ → O and O → R (O′ – Orbitally ordered orthorhombic phase, O – Orbitally disordered orthorhombic phase, R – Rhombohedral phase). In excess oxygen samples (δ = +0.02, +0.01), the O′-phase is not formed. The O → R transition temperature increases with decreasing δ from TO→R = 353 K (δ = +0.02) to TO→R = 623 K (δ = −0.03). Magnetic measurements show that all our compounds exhibit a paramagnetic-ferromagnetic transition at TC ∼ 205 K. The Arrott plots reveal the occurrence of a second order phase transition. It was found that the transition temperature TC depends on the magnitude of the applied magnetic field, which rarely happens for materials with phase transitions of the second order. It has been shown from evaluation of the Temperature averaged Entropy Change (TEC) that a wide temperature range of MCE does not satisfies the requirements of using the compounds studied as an effective magnetocaloric material for magnetic refrigeration. The substitutions in cation sublattices and oxygen non-stoichiometry have negligible effect on TC and magnetocaloric effect (MCE). To investigate the magnetic interactions responsible for the magnetic transitions, the analysis was done by using the modified Arrott plot (MAP) method. The obtained values of the critical exponents matched well with those predicted for the isotropic short range 3D-Heisenberg model.