First-order magnetic transition in Yb2Ti2O7

The very nature of the ground state of the pyrochlore compound Yb2Ti2O7 is much debated, because experimental results demonstrate evidence for either a disordered ground state or a long-range ordered ground state. Indeed, the delicate balance of exchange interactions and anisotropy is believed to lead to competing states, such as a quantum spin liquid state or a ferromagnetic state which may originate from an Anderson-Higgs transition. We present a detailed magnetization study demonstrating a first-order ferromagnetic transition at 245 and 150 mK in a powder and a single-crystal sample, respectively. Its first-order character is preserved up to applied fields of similar to 200 Oe. The transition stabilizes a ferromagnetic component and involves slow dynamics in the magnetization. Residual fluctuations are also evidenced, the presence of which might explain some of the discrepancies between previously published data for Yb2Ti2O7.