Tailoring Magnetic and Magnetocaloric Properties Towards Room Temperature by Defect Engineering at Sr Site in Ho‐Doped La _0.67 Sr _0.33 MnO ₃

We report the structural, chemical, magnetic, and magnetocaloric properties of Ho 3+ substituted La 0.67 Sr 0.33 MnO 3 : stoichiometric La 0.6 Ho 0.07 Sr 0.33 MnO 3 (LSMO‐Ho) and its Sr‐deficient composition, La 0.6 Ho 0.07 Sr 0.33‐y MnO 3 ( y = 0.07) with approximately 21% deficiency at the Sr‐site (LS d MO‐Ho). Both compounds were synthesized by the solid‐state method, and their phase formation was confirmed by X‐ray diffraction and Rietveld refinement, revealing a rhombohedral R‐3c structure, with a minor Mn 3 O 4 secondary phase in the Sr‐deficient sample. Scanning electron microscopy showed dense microstructures with sub‐5 μm grains, while field‐emission scanning electron microscopy and energy‐dispersive x‐ray spectroscopy with elemental mapping confirmed dense microstructures with uniform elemental distribution, while clearly evidencing the effect of Sr‐site deficiency on grain morphology and stoichiometry. X‐ray photoelectron spectroscopy analysis of LSMO‐Ho revealed the presence of Mn in mixed Mn 3+ and Mn 4+ oxidation states, whereas LS d MO‐Ho demonstrated an interplay involving Mn 2+ , Mn 3+ , and Mn 4+ induced by Sr site deficiency. X‐ray fluorescence spectroscopy verified the stoichiometric variations, with reduced SrO and enhanced La 2 O 3 /Ho 2 O 3 fractions in LS d MO‐Ho. Magnetic measurements demonstrated that Sr‐deficiency reduces the T C bringing it closer to room temperature. The Δ S M values were recorded for both the samples under a 5 T magnetic field, with deficient samples showing slightly lower Δ S M . Sr‐site deficiency in Ho‐doped LSMO not only shifts T C closer to room temperature but also increases the refrigerant capacity, according to the combined structural, spectroscopic, and magnetic characterizations.