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  Xu, J.; Balz, C.; Baines, C.; Luetkens, H.; Lake, B.: Spin dynamics of the ordered dipolar-octupolar pseudospin-½ pyrochlore Nd₂Zr₂O₇ probed by muon spin relaxation. Physical Review B 94 (2016), p. 064425/1-8

10.1103/PhysRevB.94.064425
Open Access Version

Abstract:
We present a muon spin relaxation study on the Ising pyrochlore Nd2Zr2O7 which develops an “all-in-all-out” magnetic order below 0.4 K. At 20 mK, far below the ordering transition temperature, the zero-field muon spin relaxation spectra showno static features and can be well described by a dynamical Gaussian-broadened Gaussian Kubo-Toyabe function indicating strong fluctuations of the ordered state. The spectra of the paramagnetic state (below 4.2 K) reveal anomalously slow paramagnetic spin dynamics and show only a small difference with the spectra of the ordered state.We find that the fluctuation rate decreases with decreasing temperature and becomes nearly temperature independent below the transition temperature, indicating persistent slow spin dynamics in the ground state. The field distribution width shows a small but sudden increase at the transition temperature and then becomes almost constant. The spectra in applied longitudinal fields are well fitted by the conventional dynamical Gaussian Kubo-Toyabe function, which further supports the dynamical nature of the ground state. The fluctuation rate shows a peak as a function of external field which is associated with a field-induced spin-flip transition. The strong dynamics in the ordered state is attributed to the transverse coupling of the Ising spins introduced by the multipole interactions.