Giant magnetocaloric effect and magnetic properties of nanocomposites of manganite Nd_1-xSr_xMnO₃ (0.0 ≤ x ≤ 0.8) synthesized using modified sol-gel method

The magnetocaloric effect in an array of nanocomposites manganite Nd_1-xSr_xMnO₃ (x = 0.0, 0.2, 0.4, 0.6 and 0.8) was reported in this study. The nanocomposites were synthesized using auto-combustion sol-gel technique where replacing Nd³⁺ by Sr²⁺ influence the structure and hence enhancing the magnetic properties and magnetocaloric effect. The synthesized nanocomposites form an orthorhombic crystal structure with Pnma space group No.62 and the average crystallite size was found to be ∼30 nm. The tunning (Mn⁴⁺/Mn³⁺) ratio varies in the nanocomposites with different concentration where the Nd_0.6Sr_0.4MnO₃ nanocomposite exhibits maximum (Mn⁴⁺/Mn³⁺) ratio. The ZFC-FC magnetization measurements indicate that all samples exhibit ferromagnetic (FM) to paramagnetic (PM) transition with increasing temperature and other phase transitions are observed for all samples except Nd_0.6Sr_0.4MnO₃ which also shows a peak Curie temperature (T_C = 256 K) in the vicinity of room temperature. The presence of FM in NdMnO₃ sample is highly enhanced via FM double exchange (DE) interaction due to self-doping process. Room temperature hysteresis loop reveals paramagnetic (PM) behaviour whereas the pronounced effect presents in Nd_0.6Sr_0.4MnO₃ compound compared to other compounds. However, all compounds exhibit FM behaviour at low temperature measurements with saturation magnetization (M_s) raising up gradually and reaching its maximum at x = 0.4. The magnetic entropy change | ΔS_M | is calculated through isotherms measurements and Nd_0.6Sr_0.4MnO₃ nanocomposite exhibits a relatively giant value of magnetic entropy (12.71 J/kg.K and 7.78 J/kg.K at around 257.5 K) under a maximum applied magnetic field of 9 T and 5 T respectively. The corresponding relative cooling power (RCP) for this compound is found accordingly as 636.9 J/kg and 349.8 J/kg. The obtained results in the wide range of temperature starting from very low temperature up to room temperature recommend Nd_0.6Sr_0.4MnO₃ compound as a good potential material for magnetic cooling.