Unveiling the Structural, Electronic and Magnetic Properties of Gd_4.5<i>A</i>_0.5Si₃O₁₃ (<i>A</i> = K, Na, and Li) Oxides With Promising Potential for Low‐Temperature Magnetic Cooling

The growing demand for solid-state magnetic cooling, leveraging the magnetocaloric effect requires the discovery of high-performing magnetocaloric materials (MCMs). Herein, a family of Gd-containing MCMs is provided, specifically the Gd_4.5A_0.5Si₃O₁₃ (A = K, Na, and Li) oxides, which demonstratse exceptional low-temperature magnetocaloric performance. Through comprehensive experimental investigations and theoretical calculations on their structural, electronic, and magnetic properties, it is unequivocally confirmed that all of them crystallize in a hexagonal apatite-type structure (space group P6₃/m), exhibiting an antiferromagnetic semiconductor ground state with magnetic ordering temperatures below 1.8 K (typically ≈0.7 K for Gd_4.5K_0.5Si₃O₁₃). Furthermore, their remarkable maximum magnetic entropy change (-ΔS_M ^max) values of 31.85 and 58.22 J kgK^-1 for Gd_4.5K_0.5Si₃O₁₃; 25.31 and 55.01 J kgK^-1 for Gd_4.5Na_0.5Si₃O₁₃; and 25.15 and 55.77 J kgK^-1 for Gd_4.5Li_0.5Si₃O₁₃, under the magnetic field changes of 0-2 and 0-5 T, respectively, surpass those of prominent low-temperature MCMs, including the commercialized Gd₃Ga₅O₁₂ (≈14.6 and 32.8 J kgK^-1) paramagnetic salt. These findings in addition to their high environmental stability position these Gd_4.5A_0.5Si₃O₁₃ oxides as exceptionally promising for practical magnetic cooling applications.