Spin Dynamics in Ferromagnets and Ferromagnetic Semiconductors Paul Crowell, University of Minnesota

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Spin Dynamics in Ferromagnets and Ferromagnetic
Semiconductors Paul Crowell, University of
Minnesota, DMR-9983777
One of the proposed technologies for information
storage is the use of patterned media, such as an
array of nanometer-scale disks, in which each
disk functions as a bit. Applications will
require that these bits be able to change state
from 0 to 1 in less than a nanosecond. In
order to understand this ultrafast switching
process, we are studying the spin dynamics of
small ferromagnetic particles. The example here
is a magnetic vortex. Like fluid flowing down a
drain, the magnetization in this disk (shown in
the bottom image on the left) circulates around
a central core, which is only about 10 nanometers
in diameter. The movie on the left shows the
dynamic response to a very fast (120 picosecond)
pulse of magnetic field. The vortex structure
buckles and then breaks up into a variety of
modes, but the circular motion around the core is
very clear. The image on the right is a
representation of the spectrum at different
magnetic fields. The peaks correspond to
different types of excitations. Understanding
these is an important step in identifying the
fundamental physics of high-speed magnetic
switching. J. P. Park et al., Phys. Rev. Lett.
89, 277201 (2002) J. P. Park et al., Phys. Rev.
B 67, 020403R (2003).
Movie of dynamics 40 picoseconds per
frame (double click below)
1 mm
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Spin Dynamics in Ferromagnets and Ferromagnetic
Semiconductors Paul Crowell, University of
Minnesota, DMR-9983777
Undergraduate Project Static Magneto-Optic
Kerr Effect Microscopy
Undergraduate Matt Landreman (Swarthmore
College) constructed a magneto-optic Kerr effect
microscope during the summer of 2003. Shown at
the right is a hysteresis loop for a single 1 mm
diameter disk of the type used in our
dynamicalexperiments. Matt is a Rhodes Scholar
at Oxford University this fall. Others who have
worked on this project include undergraduate
Jesse Berezovsky (now a graduate student at UC
Santa Barbara) and current undergraduate Paul
Kelley. The PI has coauthored 10 papers with
undergraduates over the past four years.
Freshman Antoni Wojtkowski has applied for
support under the University of Minnesota
Research Opportunities Program to work on a
project on the stability of ferromagnetic
nanoparticles in microwave fields. Local
high-school student David Tolyi will be
participating in a mentorship program in the
laboratory this winter. David will be developing
software to visualize fast magnetic processes.