Separation of quadrupolar and magnetic contributions to spin-lattice relaxation in the case of a single isotope

We present a NMR pulse double-irradiation method which allows one to separa te magnetic from quadrupolar contributions in the spin-lattice relaxation. The pulse sequence fully saturates one transition while another is observed . In the presence of a \Delta m\ = 2 quadrupolar contribution, the intensit y of the observed line is altered compared to a standard spin-echo experime nt. We calculated analytically this intensity change for spins I = 1, 3/2, 5/2, thus providing a quantitative analysis of the experimental results. Si nce the pulse sequence we used takes care of the absorbed radiofrequency po wer, no problems due to heating arise. The method is especially suited when only one NMR sensitive isotope is available. Different cross-checks were p erformed to prove the reliability of the results obtained. The applicabilit y of this method is demonstrated by a study of the plane oxygen O-17 (I = 5 /2) in the high-temperature superconductor YBa2Cu4O8: the O-17 spin-lattice relaxation rate consists of magnetic as well as quadrupolar contributions. (C) 2000 Academic Press.