Slow spin dynamics in the hyperhoneycomb lattice [(C2H5)3NH]2Cu2(C2O4)3 revealed by 1H NMR studies

We report the results of magnetic susceptibility chi and H-1 nuclear magnetic resonance (NMR) measurements on a three-dimensional hyperhoneycomb lattice compound [(C2H5)(3)NH](2)Cu-2(C2O4)(3) (CCCO). The average value of the antiferromagnetic (AFM) exchange coupling between the Cu2+ (S = 1/2) spins was determined to be J similar to 50 K from the chi measurements. No long-range magnetic ordering has been observed down to T = 50 mK, although NMR lines become slightly broader at low temperatures below 1 K. The broadening of the NMR spectrum observed below 1 K reveals that the Cu spin moments remain at this temperature, suggesting a non-spin-singlet ground state. The temperature and magnetic field dependence of 1/T-1 at temperatures above 20 K is well explained by paramagnetic thermal spin fluctuations where the fluctuation frequency of Cu2+ spins is higher than the NMR frequency of the order of megahertz. However, a clear signature of the slowing down of the Cu2+ spin fluctuations was observed at low temperatures where 1/T-1 shows a thermally activated behavior. The magnetic field dependence of the magnitude of the spin excitation gap suggests that the magnetic behaviors of CCCO are characterized as an AFM chain at low temperatures.

Automated summary

The results show that the Cu spin coupling in the three-dimensional hyperhoneycomb lattice compound CCCO has an average antiferromagnetic exchange coupling value of about 50 K, with Cu spin fluctuations slowing down at low temperatures exhibiting thermally activated behavior.