Phase lag in the amplitude modulated magnetic resonance

Response of a magnetic spin system to the amplitude modulated radiofrequenc y field is studied. Spin system is assumed to obey Bloch equations. For a s pin system resonant at Larmor frequency coo, calculations demonstrate how t he phase lags Phi (perpendicular to) and Phi (z), of magnetization componen ts M-x, M-y and M-z occur and how sensitive they are to the relaxation prop erties of the system. Relative to Larmor frequency the angular frequency of the amplitude modulation. Omega much less than omega (0), is very low, at the same time it is comparable to the relaxation rates of the spins. With r eference to the analytical solution of a damped harmonic oscillator a simpl e formula tan Phi (perpendicular to) = T-2 Omega describes the magnitude of the phase lag Phi (perpendicular to) as a function of relaxation time T-2. (C) 2001 Elsevier Science B.V. All rights reserved.