Sensitive High Frequency AC Susceptometry in Magnetic Nanoparticle Applications

Abstract

We report on the development of a sensitive high frequency susceptometer capable of measuring in the frequency range from 25 kHz up to 10 MHz with a volume susceptibility sensitivity of 3.5 × 10 -5 at 100 kHz corresponding to about 0.3 % of the measured AC susceptibility. In combination with the previous reported DynoMag system capable of measuring dynamic magnetic properties in the range from 1 Hz to 200 kHz we are thus able to measure dynamic magnetic properties between 1 Hz to 10 MHz with high magnetic sensitivity. We will show AC susceptometry applications and results within the fields of magnetic hyperthermia and dynamic magnetic characterization of magnetic nanoparticle system with different particle sizes and magnetic properties.

Effective particle magnetic moment of multi-core particles

“…2. This high frequency relaxation process is probably due to the intra-potential-well contribution of the single-domain nanocrystals to the AC susceptibility [13,16]. The Néel relaxation contribution to the AC susceptibility for the FeraSpin R particle system can best be seen in Fig.…”

“…By using different AC susceptibility models based on Debye relations for multi-core and single-core particles integrated over a size distribution (log-normal distribution) considering both Brownian and Néel relaxation behavior [12][13][14][15] and fitting the AC susceptibility data to these models, we are able to determine the particle and nanocrystal (core) size of the particle systems. The determined particle size from the AC susceptibility analysis is largely dependent on the surrounding liquid (that is the viscosity of the carrier liquid) while the determined nanocrystal (core) size is largely dependent on the nanocrystal intrinsic magnetic anisotropy.…”

“…The DynoMag system [12] was utilized between 1 Hz and 500 kHz, a lab high frequency AC susceptometer [13] was used in the frequency range between 10 kHz and 10 MHz and an additional lab high frequency susceptometer up to 1 MHz [14]. Measurements were carried out at 300 K.…”

Size-Dependent Relaxation Properties of Monodisperse Magnetite Nanoparticles Measured Over Seven Decades of Frequency by AC Susceptometry

“…We evaluated magnetic relaxations of a series of magnetite nanoparticles synthesized in our labs, using the two AC susceptibility systems designed by Acreo AB: the DynoMag [8] and HF AC Susceptometer [11]. With increasing nanoparticle size, we observed an increase in relaxation time that corresponded to a transition from Néel to Brownian relaxation [Fig.…”

Lock-In Thermography as an Analytical Tool for Magnetic Nanoparticles: Measuring Heating Power and Magnetic Fields

“…29 Some of them rely on calorimetric tests, where SPIONs temperature is directly measured during AMF stimulation using different probes (e.g., fiber optic cables, thermocouples, IR cameras). 30 Other techniques are based on magnetic measurements, such as AC magnetic susceptibility, 31,32 determination of the particles' hysteresis loops, 33 or the combination of both. 34 However, hysteresis loop determination can only be used with ferro/ ferrimagnetic particles, as SPIONs do not show magnetic hysteresis in quasi static measurements.…”