This Demonstration visualizes the dynamics in the process of magnetic resonance in which the macroscopic magnetization
of an ensemble of paramagnetic particles is exposed to the common action of a static magnetic field
and a weak magnetic field
(
) that rotates with a frequency ω around
. The motion of
is governed by the so-called
Bloch equations. The effect of
on
becomes most dramatic when the rotational frequency ω is equal to the Larmor free precession frequency
(i.e., detuning
).
Many interesting solutions are registered as bookmarks, which you can activate by clicking the small cross at the upper right corner. For example:
• The
free Larmor precession, which occurs for
, so that magnetization precesses around
at the Larmor frequency.
• The
-
pulse, for which
rotates at the Larmor frequency (
detuning = 0) and for which
is switched on for a time duration
, such that
. As a result the magnetization is flipped by
into the
-
plane.
• The
-
pulse, for which
rotates at the Larmor frequency (
detuning = 0) and for which
is switched on for a time duration
, such that
. As a result the magnetization is flipped by
to the
direction.
•
Magnetic resonance with relaxation, for which the magnetization reaches a steady state. You can play with the value of the frequency detuning
. If
or
, the effect of
is small and the steady state is close to the equilibrium magnetization along
. However, when
, the effect of
is important and the steady state is reached far from the
axis.
• A
diabatic following occurs for
, in which case the magnetization precesses rapidly around the magnetic field and therefore follows the direction of
adiabatically.
of an ensemble of magnetic moments in a magnetic field 
is determined by the Bloch equations,
is the equilibrium 
-component of 
, when all fields are 0; 
and 
are called the longitudinal and transverse relaxation rates, respectively. The total magnetic field is the vector sum of a static field 
along 
and a field 
rotating in the 
-
plane,
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