Oxygen deficiency effect on the magnetocaloric and critical phenomena for La_0.8□_0.2MnO_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 S_eff 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).