Dynamic spin fluctuations in the frustrated A-site spinel CuAl2O4

We performed nuclear magnetic resonance (NMR) and muon spin relaxation (mu SR) experiments to identify the magnetic ground state of the frustrated quantum A-site spinel, CuAl2O4. Our results verify that the ground state does not exhibit a long-range magnetic ordering, but a glasslike transition manifests at T* = 2.3K. However, the Gaussian shape and the weak longitudinal field dependence of mu SR spectra below T* show that the ground state has dynamic spin fluctuations, distinct from those of conventional spin glasses.