CdCr2O4 is a frustrated magnetic insulator featuring a large one-half magnetization plateau. The plateau arises from lattice deformations that relieve frustration, which can be seen experimentally through magnetostriction. On the experimental side, dilatometry provides a precise phase diagram in a magnetic field of up to 30 Tesla [Rossi et al., Phys. Rev. Lett. 123, 027205 (2019)]. These measurements found a significant negative thermal expansion associated with the collinear half-magnetization plateau for magnetic fields above 27 Tesla.
By comparing experiments with theoretical models, we find that this negative thermal expansion comes from a sharp, temperature-dependent drop in magnetization caused by nearly localized spin excitations in the plateau phase. Finally, I discuss how these findings may lead to a magnetocaloric effect.