Quasi-Spin Glass in a Geometrically Frustrated Magnet

A spin glass state is observed in the B-spinel ZnCr$_{2(1-x)}$Ga$_{2x}$O$_{4}$ for x $<$ 0.05 via low-temperature magnetization and specific heat. The spin glass phenomenology is conventional. The degrees of freedom (quasi-spins) that undergo freezing are unconventional, however, both in structure as well as their mutual interactions. In particular, below x = 0.05, the freezing temperature is independent of quasi-spin density, yielding a strong violation of mean field theory.