Abstract
The insulating pyrochlore compound has been shown to undergo a second order magnetic phase transition at K to a noncoplanar all-in–all-out magnetic structure of the magnetic moments. An anomalously slow paramagnetic spin dynamics has been evidenced from neutron backscattering and muon spin relaxation . In the case of this has been revealed through the strong effect of a 50 mT longitudinal field on the spin-lattice relaxation rate. Here, motivated by a recent successful work performed for and , analyzing the shape of the longitudinal polarization function, we substantiate the existence of extremely slow paramagnetic spin dynamics in the microsecond time range for . Between 1.7 and 7 K, this time scale is temperature independent. This suggests a double spin-flip tunneling relaxation mechanism to be at play, probably involving spin substructures such as tetrahedra. Unexpectedly, the standard deviation of the field distribution at the muon site increases as the system is cooled. This exotic spin dynamics is in sharp contrast with the dynamics above 100 K which is driven by the Orbach relaxation mechanism involving single magnetic moments.
- Received 22 December 2016
- Revised 10 March 2017
DOI:https://doi.org/10.1103/PhysRevB.95.134420
©2017 American Physical Society