Magnetocaloric Effect and Critical Behavior across the Second-Order Ferromagnetic-Paramagnetic Phase Transition of a...

A key challenge remains to improve or discover magnetic solids with optimal magnetocaloric effect (MCE) performance, providing a promising and environmentally friendly cooling technology. Herein, we report the crystal structure, magnetocaloric effect, and critical behavior of double perovskite NdSmNiMnO₆ synthesized by the modified sol-gel process. X-ray diffraction structural investigation reveals that NdSmNiMnO₆ crystallizes in the monoclinic P2 ₁/n (14) space group. The magnetocaloric analysis unveils a maximum magnetic entropy change of -ΔS _M ^max = 2.38 J kg^-1 K^-1 (at 0-7 T) near the ferromagnetic to paramagnetic second-order phase transition at 180 K. Furthermore, the estimated relative cooling power value increases from ∼25 to ∼182 kg^-1 K^-1 when the applied field changes up to 0-7 T, suggesting a promisor magnetic refrigerant material. The critical behavior investigated by techniques such as the modified Arrott plot, the Kouvel-Fisher method, and the critical isotherm analysis reliably yields critical exponents β = 0.469, γ = 0.978, and δ = 3.09, in agreement with the scaling hypothesis. Lastly, the renormalization group theory analysis revealed a magnetic interaction distance decaying as J(r) ∝ r ^-4.63, which is between the three-dimensional (3D) Heisenberg and the mean-field models, suggesting that the critical behavior of NdSmNiMnO₆ can be attributed to the competition between long- and short-range magnetic interactions.