Oxygen deficiency effect on the magnetocaloric and critical phenomena for La 0.8 □ 0.2 MnO 3-Δ (Δ = 0, 0.1 and 0.2) compounds: significant enhancement of relative cooling power

In this article, we focused on the study of magnetocaloric properties and the critical phenomena of $${La}_{0.8}{\square }_{0.2}Mn{O}_{3-\Delta }$$ ( $$\Delta$$ = 0, 0.1 and 0.2) manganites. The analysis of X-ray diffraction patterns shows that for $$\Delta$$ = 0 and 0.1 the samples crystallize in the rhombohedral phase with the $$R\stackrel{-}{3}C$$ space group. For $$\Delta$$ = 0.2, the refinement has reveals the coexistence of the $$R\stackrel{-}{3}C$$ rhombohedral and $$Pnma$$ orthorhombic phases. The grain size distribution for our samples was evaluated by scanning electron microscopy (SEM). The elemental and chemical properties were investigated using energy-dispersive X-ray 'EDX) measurement. The magnetic measurements prove that our samples exhibit a second-order ferromagnetic state (FM)/paramagnetic state (PM) phase transition. The study of the inverse of the magnetic susceptibility and the calculated value of Seff show the presence of a griffiths phase in $$\Delta$$ = 0.2 sample. In addition, the change in the magnetic entropy ( $$-\Delta S\left(M\right)$$ ) of representative samples was calculated using Landau theory and Maxwell relation. Remarkably, these compounds have very interesting magnetocaloric properties. In fact, the relative cooling power (RCP) reaches 126 (J. Kg−1. K−1) for an applied field at 2 T for ( $$\Delta$$ = 0.2) Which makes it considered a potentially candidate that can be used in the cooling system based on magnetic refrigeration. The calculated critical exponents values β, γ and δ using through various techniques are comparable to those predicted by the Tricritical mean field model for $$\Delta$$ = 0, $$\Delta$$ = 0.1 and by the mean field model for $$\Delta$$ = 0.2. Additionally, the magnetic interaction nature in our samples is described by the calculation of exchange distance J(r).