Orientation dependence of the magnetic phase diagram of Yb2Ti2O7

When interactions support quantum fluctuations in frustrated magnets, one may hope to realize a quantum spin liquid. Here, the authors report a detailed experimental and theoretical study of the low-temperature phase diagram of the pyrochlore quantum magnet Yb${}_{2}$Ti${}_{2}$O${}_{7}$. Despite the geometric frustration associated with this structure, the material exhibits anisotropic ferromagnetism at low temperatures. The reentrant phase diagram and the reversed anisotropy of the upper critical field reported here are, however, inconsistent with a classical description and indicate that the reentrant low-field regime is driven by quantum fluctuations.