Magnetodielectric effects at quantum critical fields in cobalt-containing garnets

Here we present a comparative study of the magnetic and crystal chemical properties of two Co2+ containing garnets, NaCa2Co2V3O12 and CaY2Co2Ge3O12. Both phases exhibit the onset of antiferromagnetic order at 8K and 6K respectively, as well as field-induced transitions in their magnetization at 1T and around 11 T. We find these field-dependent transitions correspond to quantum critical points that result in the suppression of antiferromagnetic order and that these transitions can be clearly seen using magnetocapacitance measurements. Finally, we perform detailed crystal chemistry analyses and complimentary density functional theory calculations to show that changes in the local environment of the Co-ions are responsible for differences in the two magnetic structures and their respective properties.