RSPE Seminar

Spin systems – a unique playground for nonlinear behavior

Professor Bob Camley
Department of Physics, Center for Magnetism and Magnetic Materials, University of Colorado, Colorado Springs, USA
Fulbright Distinguished Chair, University of Newcastle, NSW

Magnetic systems are ideal for nonlinear studies because one can easily control (and modify) the nature of the nonlinearity (quadratic versus cubic, for example) and there are simple physical systems to experimentally produce and measure significant nonlinear results.  Here we explore (with both theoretical and experimental results) two main areas: 

  1. The tunable generation of multiple harmonics and half harmonics for spin waves, and the creation of spin wave frequency combs.  We also study the time dependence of the generation of the comb.
  2. A magnetic analogy to the Fermi-Pasta-Ulam (FPU) problem 

The FPU system deserves a bit more explanation.  In a catalytic study, generating thousands of citations, FPU examined nonlinear elastic motion in a chain.  They found a unique result.  Instead of the ergodic behavior where energy in one mode eventually spreads out to all the modes, in the nonlinear case energy added to one mode spread only to nearby modes in frequency, but then the system would repeatedly return to the original state as time progressed. We present a theoretical study of FPU behavior in nonlinear magnetic chains. In magnetic systems the FPU behavior exists only under certain conditions and may be turned on and off by varying the strength and direction of an external magnetic field. A realistic micromagnetic model shows such behavior could be measurable. 

Bob Camley got his PhD in theoretical physics from the University of California, Irvine.  He then spent 2.5 years at the Max Planck Institut in Stuttgart and shortly after that became a faculty member at the University of Colorado. His primary research has been in the thermal and electromagnetic properties of magnetic materials, linear and nonlinear excitations, and while visiting with Peter Grunberg he and Josef Barnas developed the first theoretical explanation of the Giant Magnetoresistance effect. He also has an interest in biophysics where he and colleagues at UCCS have been working on ways to make temperature visible in MRI images.

Date & time

Fri 2 Jun 2023, 11am–12.30pm



4.03 Conference Room


Members of RSPE welcome