Large Magnetocaloric Effect in RMn₆Sn₆ Systems

Magnetic refrigeration is a more efficient and environmentally friendly technology than the conventional gas-cycle cooling. The main challenge, however, is finding materials with large enough magnetocaloric effect (MCE). A giant MCE has been found in materials with large rare-earth content but the search for earth-abundant systems has proven to be extremely challenging. Here we present our results on the Kagome magnets RMn₆Sn₆ (R=Rare Earth) that order near and above room temperature with a considerable MCE and with less than 8% rare-earth content. The materials exhibit a range of different magnetic structures depending on the specific rare earth element. We measured the MCE in these systems in order to determine how it evolves along the later Lanthanides and what magnetic transitions, structures, and anisotropies lead to the largest change of entropy. Our investigations into the RMn₆Sn₆ materials with (R=Tb, Ho, Er, and Lu) show that transitions from the paramagnetic state to a ferro- or ferrimagnetic state result in a larger entropy change than transitions between different magnetically ordered states or between para- and antiferromagnetic states. Our investigation also shows a larger MCE in the earlier lanthanides which are ferrimagnetic compared to the later Lanthanide materials which are antiferromagnetic.