Spin Excitations in Ferromagnetic Semiconductor GaMnAs Films

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Spin Excitations in Ferromagnetic Semiconductor
(GaMnAs) Films Margaret Dobrowolska,
University of Notre Dame, DMR 0603752
Microwave or femtosecond laser excitation
Microwave spin wave resonances
GaMnAs film
Purpose to explore spin dynamics through the
study of spin waves (SW) or magnons in
ferromagnetic semiconductors
Liu et al., PRB 75, 195220 (2007)
Photo-Induced Coherent Magnetization Precession
Broader impact The understanding of spin
dynamics is fundamental for building nanoscale
computational devices in which information is
encoded directly into the spin wave
(magnon). Approaches 1. Microwave spin wave
studies at Notre Dame (see top) 2. Ultrafast
magneto-optical Kerr effect at Michigan,
Vanderbilt, and UC- Berkeley (see
left). Results 1. Identified types of
non-propagating SW modes (see top) and determined
types of SW pinning. 2. Observed directly
coherent magnetization precession induced by
sub-picosecond laser pulses (see left), and
identified the temperature and field dependences
of SW modes. 3. Established spin-dynamic
parameters (magnetic anisotropy g-factor and
spin stiffness constants). 4. Identified physical
conditions that govern spin precession damping
(Gilbert damping).
H0
H?0
Wang et al., 2005 QELS PRB 75, 233308 (2007)
Qi et al., APL (2007)
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• Margaret Dobrowolska, University of Notre Dame
• DMR 0603752

Education Three undergraduate students Miss
Carissa Reynolds (Wittenberg U.), Miss Leanna
Steier (Notre Dame) and Mr. Kevin H. Miller (St.
Bonaventure University) and two grad students
(Ms. Ronda Zhou and Mr. Z. Ge) contributed to
this work. Miss Reynolds and Mr. Miller were REU
students, and Miss Steier is a Notre Dame
undergraduate whom we employ part-time. In
addition, the Ph.D. research of two graduate
students in other institutions has also benefited
from this program Mr. J. Qi at Vanderbilt U.,
and Dr. D. M. Wang who received his Ph.D. from U.
of Michigan in April 2007 and is now working at
Berkeley National Laboratory.
Societal Impact Our group has been continually
active as a resource of materials for other
groups. We are currently interacting with at
least 30 other institutions by providing them
with magnetic semiconductor specimens for their
research. The understanding of these materials
and their heterostructures, as well as of devices
based upon them developed in our laboratory, is
thus automatically of benefit to our
collaborators (including graduate students in
their Ph.D. research), who depend not only on the
specimens that we provide, but on the
intellectual input from our group in the form of
characterization and general understanding of the
properties of these materials.