Calibration of AC magnetometers for measuring magnetic fluid magnetization

AC magnetometers for characterizing magnetic nanoparticles in fluid are gaining popularity as the applications of magnetic nanoparticle fluids at AC frequencies, such as magnetic hyperthermia and magnetic particle imaging, expand[1-3]. One problem is the magnetization calibration of these magnetometers. There are practical constraints on the size and shape of the pickup coils, the vials containing fluid sample, and the near-uniform magnetic field region[2]. These constraints lead to a geometry in which the sample is too small to approximate as a long rod but too large for a point-dipole approximation[4]. We will present theoretical calibration factor calculations for these intermediate geometries along with experimental verification. In this geometry, the calibration factor is particularly sensitive to changes in the sample aspect ratio and distribution of magnetic moment within the sample, moreso than in [5]. Thus, samples that are inhomogeneous or in which evaporation occurs require additional calibration steps.

 

[1] Z. Boekelheide et al, JMMM (2021)

[2] I. Rodrigo et al, International Journal of Hyperthermia (2020)

[3] P. Lenox et al, IEEE Magnetics Letters (2018)

[4] R. L. Fagaly, Review of Scientific Instruments (2006)

[5] Z. Boekelheide and C. L. Dennis, AIP Advances (2016)