Ferromagnetically interacting Ising spins on the pyrochlore lattice of corner-sharing tetrahedra form a highly degenerate manifold of low-energy states. A spin flip relative to this “spin-ice” manifold can fractionalize into two oppositely charged magnetic monopoles with effective Coulomb interactions. To understand this process, we have probed the low-temperature magnetic response of spin ice to time-varying magnetic fields through stroboscopic neutron scattering and SQUID magnetometry on a new class of ultrapure Ho₂Ti₂O₇ crystals. Covering almost 10 decades of time scales with atomic-scale spatial resolution, the experiments resolve apparent discrepancies between prior measurements on more disordered crystals and reveal a thermal crossover between distinct relaxation processes. Magnetic relaxation at low temperatures is associated with monopole motion through the spin-ice vacuum, while at elevated temperatures, relaxation occurs through reorientation of increasingly spin-like monopolar bound states. Spin fractionalization is thus directly manifest in the relaxation dynamics of spin ice.

共享角四面体烧绿石晶格上的铁磁相互作用 Ising 自旋形成了高度简并的低能态流形。相对于这种“自旋冰”流形的自旋翻转可以分解为两个带相反电荷的磁单极子，并具有有效的库仑相互作用。为了理解这个过程，我们通过频闪中子散射和 SQUID 磁力测定法在一类新型超纯 Ho ₂ Ti ₂ O _{7 上}探测了自旋冰对时变磁场的低温磁响应晶体。这些实验涵盖了近 10 个具有原子级空间分辨率的时间尺度，解决了先前对更无序晶体的测量之间的明显差异，并揭示了不同弛豫过程之间的热交叉。低温下的磁弛豫与通过自旋冰真空的单极运动有关，而在高温下，弛豫通过越来越类似自旋的单极束缚态的重新定向而发生。因此，自旋分级直接体现在自旋冰的弛豫动力学中。