3d-4f spin interaction induced giant magnetocaloric effect in zircon-type DyCrO₄ and HoCrO₄ compounds

We have investigated the influence of 3d-4f spin interaction on magnetic and magnetocaloric properties of DyCrO₄ and HoCrO₄ compounds by magnetization and heat capacity measurements. Both the compounds exhibit complicated magnetic properties and huge magnetic entropy change around the ferromagnetic transition due to the strong competition between ferromagnetic and antiferromagnetic superexchange interactions. For a field change of 8 T, the maximum values of magnetic entropy change (Δ S M m a x), adiabatic temperature change (Δ T a d), and refrigerant capacity (RC) reach 29 J kg^-1 K^-1, 8 K, and 583 J kg^-1, respectively, for DyCrO₄ whereas the corresponding values for HoCrO₄ are 31 J kg^-1 K^-1, 12 K, and 622 J kg^-1. Δ S M m a x, Δ T a d, and RC are also quite large for a moderate field change. The large values of magnetocaloric parameters suggest that the zircon-type DyCrO₄ and HoCrO₄ could be the potential magnetic refrigerant materials for liquefaction of hydrogen.