Disk Shaped Magnetic Thin-Film Nanoparticles Tailored for Optimal MPI Signal Generation

Abstract

Magnetic Particle Imaging (MPI) generates signals through the nonlinear magnetization response of magnetic nanoparticle tracers to an external magnetic field. The common tracers used so far are superparamagnetic iron oxide (SPIO) nanoparticles. These particles exhibit a modest saturation magnetization and follow a Langevin-type magnetization curve, which restricts their dM/dH response. Consequently, this leads to a limited generation of higher harmonic signals in magnetic field drive oscillations, thereby affecting the sensitivity and spacial resolution achievable in MPI setups.

In our research, we have adopted a top-down approach for nanoparticle fabrication. This process begins with the sputter-deposition of multilayers on a Germanium sacrificial layer, which is evaporated onto a silicon wafer. From these layers, circular nanoscale islands are then patterned. The analysis of the magnetic properties of these islands revealed an M(H) loop characterized by a narrow switching field distribution and coercive fields below 1 mT. To create a nanoparticle suspension, these circular islands were detached from the wafer through the dissolution of the sacrificial layer. The recorded magnetic particle spectra of these disk-shaped magnetic nanoparticles showed a significant enhancement in the amplitudes of the higher harmonics when compared to perimag® particles. This advancement allows for the detection of signals up to the nth harmonic, leading to a marked improvement in MPI performance.