  Magnetic nanoparticles have proven to be valuable for biomedical
applications. A prerequisite for the efficiency of these applications are
precisely characterized particles. Thermal Noise Magnetrometry (TNM), unlike
any other magnetic characterization method, allows to characterize the
particles without the application of an external excitation. We present a
theoretical framework to model the experiment in order to examine the magnetic
noise power properties of particle ensembles in TNM and optimize the geometry
of the nanoparticle sample. An optimized sample geometry is calculated to
maximize the noise power measured by the detector. The theoretical framework
and the newly designed sample holder are validated by measuring a sensitivity
profile in the setup. The optimized sample holder increases the noise power
with a factor of 3.5 compared to the regular sample holder, while its volume is
decreased by more than half. Moreover, the experimental profiles are consistent
with the simulated counterparts, confirming the relevance of the theoretical
framework. These results contribute to the further establishment of TNM as
magnetic nanoparticle characterization method.
