EXPERIMENTAL
The spin-lattice relaxation times were measured by adiabatic
fast passage. In adiabatic fast passage, the magnetization vector
follows the precession of the effective magnetic field obeying the
equation
dH
0 << Jl H2 (12)
dt 1
where H1 is the applied rf field [5]. If the static magnetic field,
Ho, is symmetrically modulated by a sinusoidal or triangular sweep,
and if the time spent in resonance is short compared to T1, then at
equilibrium the signal on the return trace will be equal in amplitude
but inverted from that on the forward trace.
The magnetization at any time t, M1, is given by
1 exp(-t /T)
M = M (13)
1 expl-t/T (3)
where M is the magnetization at equilibrium in the H field [5].
O O
A modification of the above method is useful for T1 measurement.
The signal is no longer centered in the sweep field so there are
unequal time intervals above and below resonance. The time interval
difference, At, may be adjusted such that the signal vanishes on the
return trace as the magnetization returns to equilibrium. By knowing
the period of the sweep, P, and At, T1 is determined from the equation