Quality Factor Characterization of Magnetic Materials using Magnetic Force Macroscopy

Charles Brown and Mike Hepler

University of Minnesota

Methods of Experimental Physics Spring 2012

Abstract

Using a technique dubbed magnetic force macroscopy, this experiment attempted to characterize changes in the magnetic properties A36 steel in response to permanently induced strain. As a magnetic material is strained, it is expected that magnetic domain walls will increase in number and will be pinned to the deformations created as the metal is stretched. Using an oscillating cantilever with a strong neodymium magnet at the tip, we investigated the energy loss of the cantilever's motion due to the magnetic field's interaction with the magnetization present in the metal sample. The energy loss due to the magnetic interactions was expected to produce changes in the shape of the resonance curve of the cantilever, and could therefore be measured by determining the quality factor of the cantilever's response. Our team attempted to identify strained regions by determining this Q-factor at regular intervals over several samples. Due to what we believe is a lack in the sensitivity of our equipment, we were unable to find any measurable change in the shape of the resonance curves, and thus no measurable change in energy loss was observed.