arXiv subjects

Thomas Veile

Publications and source records attributed to Thomas Veile.

4 recordsLinked to original sources

arXiv2026

The impact of sample insulation on estimating the heating power of magnetic nanoparticles by AC calorimetry

Correct estimation of the heating power of magnetic nanoparticles is important for magnetic hyperthermia treatment. This work investigates the impact of sample insulation in AC calorimetry. We show that temperature increase in the insulation can lead to systematic errors when estimating the heating power by the corrected slope method. The errors arise if the temperature of the sample environment is kept fixed at its initial temperature in the data analysis. To correct for this, we propose the use of a local temperature difference between the sample and the sample environment.

physics.app-ph↗

arXiv2026

Enhanced nanocomposite susceptibility by field-alignment of superparamagnetic particles

Nanocomposites comprised of insulated magnetic single-domain particles are promising candidates for high-frequency, eddy current free, soft magnetic materials, but tend to suffer from low magnetic susceptibility ($<20$). Particle alignment has been proposed to increase nanocomposite susceptibility and reduce magnetic losses but experimental verification has been lacking. Here, magnetic nanocomposites containing 3-57 vol\% field-aligned 11$\pm$3 nm maghemite particles in a poly-vinyl matrix were investigated for potential use as high-frequency inductor core materials. The particles were aligned by a homogenous static alignment field during nanocomposite drying, fixating the particle orientation. Particle aggregation was disproved by small-angle scattering. The dependence of the alignment field strength and particle concentration on the nanocomposite's susceptibility and hysteresis losses were investigated from DC up to 922 kHz by vibrating sample magnetometry, AC-susceptibility and high-frequency hysteresis measurements. Nanocomposite susceptibility increased super-linearly with particle fraction due to weak particle interactions. Alignment of the particles increased the nanocomposite susceptibility from 21 to 50 for samples with a particle content of 57 vol\%. Hence, the synergy between particle alignment and interaction allows for a higher than expected susceptibility of nanocomposites. The results show that magnetically aligning particles in a nanocomposite reduces magnetic losses when using well-dispersed single-domain superparamagnetic nanoparticles. Measured nanocomposite susceptibility could be modelled by a combination of directional dependent Debye-models including mean-field interaction effects and partial particle alignment. Measured susceptibility of 50 is among the highest obtained for nanocomposites, making it a relevant candidate for applications in power electronics.

physics.app-ph↗

arXiv2025

AC Magnetometry Loop Tracer Compatible with Magnetic Calorimetry for Power Loss Analysis

Magnetic nanoparticles (MNPs) have garnered significant attention for various applications in the high-kHz-to-MHz range, although their magnetic characterization at these operational conditions has been limited. However, a number of recent studies have showcased high-frequency and high-field amplitude AC magnetometry loop tracers capable of retrieving the magnetic AC hysteresis curve and the associated magnetic properties. In this paper, we present an easily constructable loop tracer that is retrofitted into an existing AC calorimetry setup. This enables the loop tracer to function simultaneously with the AC calorimetry setup and also to be run as a high-frequency AC susceptometer. The loop tracer is shown to work in the frequency range 160-922 kHz with maximum applied fields from 18 to 46 mT depending on the frequency. An iron oxide nanoflower sample is used to test the loop tracer, showcasing high reproducibility in measured magnetic parameters as well as quantitative agreement between the different measurement methods in the setup.

physics.ins-det↗

arXiv2025

Printable Nanocomposites with Superparamagnetic Maghemite ($\gamma$-Fe$_2$O$_3$) Particles for Microinductor-core Applications

We here present printable and castable magnetic nanocomposites containing superparamagnetic 11$\pm$3 nm $\gamma$-Fe$_2$O$_3$ particles in an insulating poly-vinyl alcohol polymer matrix. The nanocomposites feature well-dispersed particles with volume fractions between 10 and 45 \%, as confirmed by small-angle neutron scattering. The magnetic volume susceptibility is as high as 17, together with negligible hysteresis at low frequency, and constant AC-response up to the high-kHz range. Measured hysteresis curves at 100-900 kHz with up to 110 mT induced $B$-fields in the nanocomposite show that power losses depend on $B$-field squared, and frequency to the power of 1-1.3. The only loss mechanism in the nanocomposite is hysteresis losses at $>$100 kHz frequencies, where the largest particles in the 11$\pm$3 nm distribution transition from the superparamagnetic to blocked regime. To mitigate the resulting hysteresis losses (up 10$^2$-10$^5$ kW/m$^3$) a more narrow particle size distribution could be used for future materials. The presented material is eddy current-free and easily integrated into micro-fabrication protocols, as we demonstrate by fabrication of 3-turn print circuit board based inductors with cast/manual printed nanocomposite inductor cores, on which induction has been measured up to 100 MHz.

cond-mat.mes-hall↗