Monopolar and dipolar relaxation in spin ice Ho 2 Ti 2 O 7

• Published in: Science advances 2021-06, Vol.7 (25)
• Main Authors: Wang, Yishu, Reeder, T., Karaki, Y., Kindervater, J., Halloran, T., Maliszewskyj, N., Qiu, Yiming, Rodriguez, J. A., Gladchenko, S., Koohpayeh, S. M., Nakatsuji, S., Broholm, C.
• Format: Article
• Language: English
• Subjects: CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
• ISSN: 2375-2548; 2375-2548
• DOI: 10.1126/sciadv.abg0908

The fractionalization of magnetic dipoles into monopoles is revealed through a crossover in the relaxation dynamics of spin ice. 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 Ho 2 Ti 2 O 7 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.