Investigation of the Emerging Magnetic Behavior in a Breathing Spinel Material

Considered one of the best candidates for geometric frustration in three-dimensions, the corner sharing tetrahedral network known as the Pyrochlore lattice is exhibited in various materials including spinels with general formula AM₂X₄ (A = alkali and alkaline earth metals, heavier 3d transition metals and Ge, Cd and Hg; M = transition and post transition metals; X = group 16 elements). However, the addition of two different size cations on the A site leads to the formation of a unique lattice type called the breathing pyrochlore lattice, which has been discovered in materials with the general formula AA'Cr₄X₈. The partial substitution of the A site atom results in the formation of two inequivalent tetrahedra with bond distances d, d' defined by a breathing ratio d′/d and two inequivalent nearest-neighbor magnetic exchange interactions J, J'. The newly introduced degrees of freedom in the breathing pyrochlore lattice provides a certain level of tunability of the frustration within the lattice leading to a plethora of exotic magnetic states. In this talk, I will present the chemical tuning effect of the A and A' atomic sites on the structure, breathing ratio and magnetic behavior in the breathing spinel CuA'Cr₄Se₈ family. A highly frustrated magnetic nature with complex magnetic order was discovered for CuAlCr₄Se₈, with a T_f ~ 13 K. The highly frustrated magnetic nature, exclusion of expensive rare-earth elements and low transition temperatures makes the breathing spinel materials attractive magnetocaloric candidates for low temperature applications. The complex magnetic order in the breathing spinel family provides a unique avenue to generate a large magnetocaloric effect (MCE) through the use of highly frustrated magnetic materials. Through an indirect measurement method, we have assessed the potential magnetocaloric effect within the breathing spinel CuA'Cr₄Se₈ family.