a Department of Physics, Oregon State University, Corvallis, OR 97331-6507, USA
b Department of Chemistry, Oregon State University, Corvallis, OR 97331-6507, USA
Abstract:
We report 63,65Cu spin–lattice relaxation rates measured by nuclear quadrupole resonance (NQR) in the delafossite compound CuYO2 and CuYO2:Ca over a temperature range from 200 to 450 K. CuYO2:Ca is a prototype transparent oxide exhibiting p-type electrical conductivity. Relaxation rates in CuYO2:Ca are enhanced by one to two orders of magnitude relative to undoped material, exhibit much stronger temperature dependence, and contain contributions from magnetic and quadrupolar relaxation mechanisms with roughly equal strengths. Relaxation in undoped CuYO2 is of purely quadrupolar origin and is attributed to interactions with lattice phonons. The main focus of this paper is the magnetic contribution to the relaxation rate in CuYO2:Ca which is attributed to the hyperfine fields of carriers. It is argued that the dynamics of the hyperfine field are dominated by the hopping rate for carrier transfers between neighboring atoms in the copper planes of the delafossite structure. Comparison of the magnetic relaxation rates with the DC conductivity permits an estimate of the carrier concentration and mobility.