Rotating Frame Analog of Spin-Locking and Spin-Lattice Relaxation in the Doubly Rotating Frame

摘要

The present paper reports the achievement of the rotating-frame analog of spin-locking and its application to the precise measurements of the spin-lattice relaxation time T_(1DR) in the doubly rotating frame. After the magnetization is aligned along the resonant RF field H_(1), a pulse sequence of a low-frequency oscillating magnetic field at exact resonance is applied perpendicular to H_(1). We have overcome several technical difficulties arising from the fact that the rotating-wave approximation is not valid for the low-frequency field. We have theoretically derived an expression of T_(1DR)~(-1) due to fluctuating magnetic dipole interactions in the weak collision case and found an important relation among the spinlattice relaxation rates T_(1)~(-1), T_(1ρ)~(-1), and T_(1DR)~(-1). This relation can be used to ascertain whether the relaxation is only due to the fluctuating magnetic dipole interactions between like spins. The experiment was carried out on ~(1)H nuclei in tetramethylammonium iodide (CH_(3))_(4)NI and the temperature dependence of T_(1DR)~(-1) was measured together with that of T_(1)~(-1) and T_(1ρ)~(-1). The activation energies and the preexponential factors of Arrhenius expressions of the correlation times are newly determined.