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

Host:  Ramesh
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