Sensitive Measurement of Parallel and Transverse Susceptibility by Alternating Gradient Magnetometry

Reversible susceptibility tensor measurements reveal important information about the switching fields and anisotropies of magnetic materials. We show that a simple reconfiguration of an alternating gradient magnetometer can be used to measure both reversible parallel and transverse susceptibilities with high sensitivity. It is demonstrated that positioning the sample off-axis with respect to the magnetometer gradient field coils results in a signal at twice the frequency of the gradient field that is directly proportional to the reversible susceptibility. Offsetting the sample along the x-axis results in a sensor signal proportional to the reversible parallel susceptibility, while rotating the sample holder by 90 degrees and offsetting it along the y-axis results in a sensor signal proportional to the reversible transverse susceptibility. Examples of reversible parallel and transverse susceptibility measurements of aligned nanoparticle systems will be demonstrated.