Investigation of Magnetocaloric Effect and Critical Field Analysis of Nd0.7−xLaxSr0.3MnO₃ (x = 0.0−0.3) Manganites

This research explored the temperature dependence magnetization, magnetocaloric effect, and critical field analysis of Nd 0.7−x La x Sr 0.3 MnO 3 (x = 0.0, 0.1, 0.2 and 0.3) manganites samples synthesized through solid state reaction route. The substitution of La 3+ at Nd 3+ site enhances the A-site average ionic radius ( r A ) from 1.321 Å (for x = 0.0) to 1.348 Å (for x = 0.3). An increase in r A reduced the internal chemical pressure inside the lattice such that the Mn–O–Mn bond angle approached 180°. In addition, an increase in Mn–O–Mn bond angle supresses the spin-lattice interaction, which consequently reduces the change in maximum magnetic entropy ( Δ S M max ) at the magnetic transition temperature. This implies that variation of A-site average ionic radius influences the change in maximum magnetic entropy. The critical behavior of the manganite samples was addressed based on the data of magnetization measurements around the transition temperature T C . Various techniques such as modified Arrott plot, a Kouvel–Fisher method, and critical isotherm analysis were used to measure the values of the ferromagnetic transition temperature TC, as well as the critical exponents of β , γ , and δ . The magnetic order parameter n is very well obeyed with scaling relation with change in magnetic entropy.