Special
Condensed Matter Physics Seminar
Note special time and place!
2 p.m., Tuesday, September 23, 2003
Room 1302, Nuclear Engineering Bldg.
Parametric
Pumping, Nonlinear Spin Waves, and Spin Wave Instability in Permalloy Films
Carl E. Patton
(Department of Physics, Colorado State University)
Abstract: The damping in ferromagnetic films is a critical
consideration for magnetic storage applications. It is often assumed that the
damping from low power ferromagnetic resonance (FMR) linewidth measurements is
applicable to switching and flux reversal. New FMR measurements at high
microwave power show that nonlinear effects can be important even for very small
precession angles. The data show features which are well known for spin wave
instability processes in ferrites, as well as new features unique to metallic
films. Of particular note are the very small precession angle, on the order of
a few degrees, for the onset of nonlinear damping.The
measurements were made with a high power spectrometer at a nominal frequency of
10 GHz for in-plane and perpendicular-to-plane magnetized 100 – 300 nm thick
permalloy films. The data show a clear saturation of the uniform mode FMR line
and, in addition, a broad subsidiary absorption peak below the FMR field. All
of these effects occur for relatively low powers, small microwave field
amplitudes, and small precession angles.
Measurements of the threshold field
versus static field H profiles, called “butterfly
curves”, in the subsidiary absorption region show a distinct structure and a
characteristic high field divergence points which mark the low frequency band edge of
the spin wave band at one-half the pump frequency for the film under test. A
theory of spin wave instability processes in thin films has also been
developed. Fits to the data give new information on the wave vector dependence
of the spin wave linewidth and relaxation rate in thin films, as well as the
critical modes for the instability response.
This work was supported in part by the National Science
Foundation, DMR-0108797, the United States Office of Naval Research,
N00014-03-1-0070, the United States Army Research Office, DAAD19-02-1-0197, and
the National Institute of Standards and Technology Nanomagnetodynamics Program
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Host: Ramesh
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