Magnetization Dynamics and Random Matrices
Robert McMichael
Metallury Division, Material Science Engineering Laboratory, NIST
Tuesday, January 28, 2003 15:00-16:00,
Room 145, NIST North (820)
Gaithersburg
Tuesday, January 28, 2003 13:00-14:00,
Room 4550
Boulder
Abstract:
One interesting consequence of the link between the magnetic moment
and the spin angular momentum of electrons is that the magnetization
precesses around the effective field in a way that is analogous to
the precession of a top in the gravitational field. Typical precession
frequencies are in the GHz range. Damping processes allow the
magnetization to come to equilibrium in a few nanoseconds, a time that
is becoming slow relative to data rates in disk drives, magnetic
memory chips and sensors.
Ferromagnetic resonance experiments use the width of the peak in
susceptibility at the magnetization precession frequency to measure
magnetization damping. These measurements are generally clouded by
the presence of material inhomogeneities that broaden the
ferromagnetic resonance lines. In this talk, I will give an
introduction to ferromagnetic resonance and three models of the added
line width due to inhomogeneities: one that ignores magnetic
interactions, one that handles weak inhomogeneities while accounting
for interactions, and a new model that links the two older models.
This new model requires finding the eigenvalues and eigenmodes of a
Hermitian matrix with Fourier components of the random inhomogeneity
in the off-diagonal terms. Finally, I will touch on the possible
relationships between this work and random matrix theory and
localization theory.
Contact: M. J. DonahueNote: Visitors from outside NIST must contact
Robin Bickel; (301) 975-3668;
at least 24 hours in advance.
|
