Magnetism, Magnetocaloric, and Universality Class of Rare Earth Doped La _0.6‐ <i> _x </i> Eu <i> _x </i> Ca _0.4 MnO ₃ Manganite

ABSTRACT This work investigates the effect of rare earth substitution at the A‐site of La 0.6‐ x Eu x Ca 0.4 MnO 3 ( x = 0, 0.1) on the structural, magnetic, and magnetocaloric properties, with focus on the influence of ionic radius reduction on cooling performance. Polycrystalline samples synthesized via standard solid‐state reaction were structurally characterized using X‐ray diffraction, confirming single‐phase formation with orthorhombic symmetry (Pnma space group). Magnetic characterization reveals a pronounced paramagnetic–ferromagnetic transition whose temperature exhibits strong dependence on lanthanide substitution. The Curie temperature () demonstrates significant reduction from 260 K for the parent compound (x = 0) to 135.5 K for the europium‐doped variant ( x = 0.1), attributable to decreased ionic radius at the A‐site. Critical analysis of the phase transition through universal curve construction consistently confirms second‐order magnetic behavior. Comprehensive evaluation of magnetocaloric parameters reveals exceptional cooling performance, with the europium‐doped compound exhibiting a magnetic entropy change (||) of 3.33 J.kg −1 .K −1 under 5 T applied field. The full‐width at half‐maximum of spans 102 K, yielding a substantial refrigerant capacity of 157 J·kg − 1 . Most notably, the relative cooling power demonstrates remarkable enhancement from 210 to 340 J·kg − 1 at 50 kOe, representing a 60% improvement over the undoped compound. Additional thermodynamic parameters including adiabatic temperature change (), temperature‐span averaged entropy change, and the field‐normalized refrigerant capacity were quantified to establish comprehensive structure property relationships. These findings suggest that rare earth substitution at the A‐site can effectively modify the magnetocaloric response in perovskite manganites, indicating their potential for magnetic refrigeration applications.