Magnetic Sensor Principle for Susceptibility Imaging of Para- and Diamagnetic Materials

Abstract

In ferromagnetic materials, magnetic domain walls interact with microstructure over similar mechanisms as dislocations do. Under the absence of stress as an additional influence, the magnetic properties of these materials are often correlated with mechanical-technological characteristics such as hardness and strength. This fundamental observation is the basis of micro-magnetic materials characterization. It is not yet well known, but quite legitimate to assume that such a correlation also exists between magnetic and mechanical properties of para- and diamagnetic materials, since the interactions on the electron spin level depend on the molecular structure and determine the magnetic behavior. Similar effects are known to exist in the electrical domain. As an example, the electrical conductivity of nonmagnetic materials such as aluminum or nickel based alloys, which can be assessed non-destructively using eddy current impedance measurements, is affected by stress and dislocation density. Much less is known about the correlation between the mechanical properties and the magnetic susceptibility of non-ferromagnetic materials such as graphite, aluminum and plastics. Today, there is no commercialized non-destructive method which uses the concept of magnetic susceptibility measurements for the characterization of dia- and paramagnetic materials. This article proposes a force-based magnetic sensor principle for susceptibility imaging of such materials.