Accurate Prediction of the Magnetic Ordering Temperature of Ultralow-Temperature Magnetic Refrigerants.

Adiabatic demagnetization refrigeration is known to be the only cryogenic refrigeration technology that can achieve ultralow temperatures (≪1 K) at gravity-free conditions. The key indexes to evaluate the performance of magnetic refrigerants are their magnetic entropy changes (-Δ S _m ) and magnetic ordering temperature ( T ₀ ). Although, based on the factors affecting the -Δ S _m of magnetic refrigerants, one has been able to judge if a magnetic refrigerant has a large -Δ S _m , how to accurately predict their T ₀ remains a huge challenge due to the fact that the T ₀ of magnetic refrigerants is related to not only magnetic exchange but also single-ion anisotropy and magnetic dipole interaction. Here, we, taking GdCO ₃ F ( 1 ), Gd(HCOO)F ₂ , Gd ₂ (SO ₄ ) ₃ ·8H ₂ O, GdF ₃ , Gd(HCOO) ₃ and Gd(OH) ₃ as examples, demonstrate that the T ₀ of magnetic refrigerants with very weak magnetic interactions and small anisotropy can be accurately predicted by integrating mean-field approximation with quantum Monte Carlo simulations, providing an effective method for predicting the T ₀ of ultralow-temperature magnetic refrigerants. Thus, the present work lays a solid foundation for the rational design and preparation of ultralow-temperature magnetic refrigerants in the future.