Low-field octupoles and high-field quadrupoles in URu2Si2

The recent experimental finding of large-amplitude antiferromagnetism induced by uniaxial strain shows that the "hidden" low-field order of URu2Si2 breaks time reversal invariance. We propose a new crystal field model which supports T(beta)z octupolar order in the low-field phase, and quadrupolar order in a disjoint high-field phase. The temperature dependence of the linear and third order magnetic susceptibility is in good agreement with the observed behavior.