Magnetic transition, long-range order, and moment fluctuations in the   pyrochlore iridate Eu2Ir2O7
  Muon spin rotation and relaxation experiments in the pyrochlore iridate Eu2Ir2O7 yield a well-defined muon spin precession frequency below the metal-insulator/antiferromagnetic transition temperature TM = 120 K, indicative of long-range commensurate magnetic order and thus ruling out quantum spin liquid and spin-glass-like ground states. The dynamic muon spin relaxation rate is temperature-independent between 2 K and ~TM and yields an anomalously long Ir^{4+} spin correlation time, suggesting a singular density of low-lying spin excitations. Similar behavior is found in other pyrochlores and geometrically frustrated systems, but also in the unfrustrated iridate BaIrO3. Eu2Ir2O7 may be only weakly frustrated; if so, the singularity might be associated with the small-gap insulating state rather than frustration. 
Songrui Zhao. J. M. Mackie, D. E. MacLaughlin, O. O. Bernal, J. J.   Ishikawa, Y. Ohta, and S. Nakatsuji
cond-mat.str-el