Magnetization dynamics in bistable systems

Sammanfattning: The magnetization dynamics in ferromagnetic materials will depend on the specific shape of the system’s energy landscape. In most systems, the energy landscapes can be approximated as paraboloids, resulting in a typical ellipti- cal precession of the magnetization. However, this model is not always appli- cable to more complex potentials, which can present exotic precessions. The aim of this project was to measure the magnetization dynamics in a system where a non-parabolic potential was expected. From the dynamics, it would then be possible to estimate the energy potential of the system. In order to measure magnetization dynamics, time-resolved MOKE (magneto-optic Kerr effect) measurements were performed using a pump-and-probe tech- nique. A permalloy (Fe20Ni80) thin film with an uniaxial in-plane anisotropy was used as a sample, presumably presenting a bistable energy potential with two close minima at certain applied external magnetic fields. By measuring one component of the magnetization in the plane of the sample, the shape of the precession in this landscape could be extracted. The results show the expected parabolic precessions at higher external fields, from which energy landscapes could be constructed. The dynamics measured at one particular field also indicate a bistable energy potential although no exotic precessions were found.