Structural, Magnetic, and Magnetocaloric Properties of La0.67Sr0.33−xKxMn0.95Ni0.05O3 Manganites (x = 0.10, 0.125, and 0.15): A-site Doping

Polycrystalline powder samples of La_0.67Sr_0.33−xK_xMn_0.95Ni_0.05O₃ (x = 0.1, 0.125, 0.15) (LSKMNO) were prepared using the sol–gel method (S-G) in this study. The influence of K⁺ doping was systematically investigated on the lattice structure, morphology, and magnetic and magnetocaloric effect (MCE) of LSKMNO. Through the X-ray diffraction (XRD) to confirm the rhombohedral structure of LSKMNO. The magnetic results showed that the Curie temperature (T_C) and the maximum magnetic entropy change (\(\mathit-{\mathit\Delta\textit{S}}_\textit{M}^\text{max}\)) increase with the K⁺ doping for LSKMNO. The T_C and \(\mathit-{\mathit\Delta\textit{S}}_\textit{M}^\text{max}\) for LSKMNO (x = 0.15) were 319 K and 3.59 J/(kg·K) when the external magnetic field (H) was 5 T, respectively. Arrott curve and normalized magnetic entropy curve (\({\mathit\Delta\mathit S}_\textit{M}\mathit/{\mathit\Delta\mathit S}_\textit{M}^\text{max}\mathit-\theta\)) are plotted to prove that LSKMNO undergoes a second order magnetic phase transition at the T_C attachment.