Giant reversible magnetocaloric effect in the pyrochlore Er2Mn2O7 due to a cooperative two-sublattice ferromagnetic order

Most magnetic refrigeration materials showing a large and reversible magnetocaloric effect (MCE) undergo a second-order ferromagnetic (FM) transition involving large-moment magnetic species on one sublattice. A stronger MCE is expected near a cooperative FM order of two or more magnetic species with large magnetic moments residing on different sublattices, but experimental realizations are rare. Here we report on the discovery of large MCE in the cubic pyrochlore Er2Mn2O7 near its second-order FM transition at T-c approximate to 34 K; under the magnetic field change of 1 and 5 T, the maximum magnetic entropy change -Delta S-M is 5.27 and 16.1 J kg(-1) K-1, and the estimated magnetic refrigerant capacity reaches 68 and 522 J kg(-1), respectively. These latter values are among the largest for the known MCE materials. The observed giant and reversible MCE in Er2Mn2O7 is mainly attributed to the large saturation moment of 18.9 mu(B) per formula unit owing to a simultaneous FM ordering of the rear-earth Er3+ and transition-metal Mn4+ localized moments. Our results suggest that Er2Mn2O7 pyrochlore is a promising candidate for magnetic refrigeration applications in the temperature range 20-80 K. More importantly, this work provides a new material system for developing high-performance MCE materials that can exhibit a strongly coupled FM transition involving two magnetic sublattices of large local moments in a single-phase material.