T-1P IN NUCLEAR-QUADRUPOLE RESONANCE - A THEORETICAL-STUDY

A new NQR method of measuring the spectral density of slow motions in solids is proposed. It is shown that also in NQR a 90 degrees phase sh ift of a resonant rf magnetic field following a 90 degrees pulse locks the nuclear magnetization in a 'rotating frame' similarly as in NMR. The spin-lattice relaxation time T-1 rho of the locked magnetization i s calculated in general for an arbitrary spin. It is assumed that the fluctuations of the EFG tensor dominate the spin-lattice relaxation. T he calculations show that T-1 rho depends on the spectral density J(om ega) of the electric quadrupole fluctuations at the NQR frequencies, a nd also at a low frequency Omega. Here Omega approximate to gamma B-1 kHz depends on the orientation of the rf magnetic field in the princip al-axis system of the EFG tenser. The term containing J(Omega) in the expression for T-1 rho(-1) depends on the orientation of the rf magnet ic field in the principal-axis system of the EFG tensor, only through the orientation dependence of Omega. This term vanishes when the elect ric quadrupole fluctuations do not modulate the frequency of the NQR t ransition excited by the rf magnetic field. Two particular examples: I = 1 and I = 3/2 are worked out in details. (C) 1997 Elsevier Science B.V.