| Zugriffsnummer | 35525 |
| Dokumenttyp | Zeitschriftenartikel |
| Sprache | Englisch |
| Titel | Magnetic-field dependence of Brownian and Néel relaxation times |
| Autor(in); Institution |
Dieckhoff, J.; Institut für Elektrische Messtechnik und Grundlagen der Elektrotechnik, TU Braunschweig, Braunschweig, GERMANY
Eberbeck, Dietmar; 8.2, Biosignale, PTB-Berlin
Schilling, M.; Institut für Elektrische Messtechnik und Grundlagen der Elektrotechnik, TU Braunschweig, Braunschweig, GERMANY
Ludwig, F.; Institut für Elektrische Messtechnik und Grundlagen der Elektrotechnik, TU Braunschweig, Braunschweig, GERMANY
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| Quelle/Jahr | Journal of Applied Physics: 119 (2016), 4, 043903-1 - 043903-8 |
| ISSN | 0021-8979 (PRINT) ; 1089-7550 (ONLINE) |
| DOI | |
| Verlag | Melville, NY: AIP |
| Freie Schlagworte | Relaxation times ; Alternating current power transmission ; Magnetic fields ; magnetic fields measurements ; Magnetic moments |
| Zusammenfassung | The investigation of the rotational dynamics of magnetic nanoparticles in magnetic fields is of academic interest but also important for applications such as magnetic particle imaging where the particles are exposed to magnetic fields with amplitudes of up to 25 mT. We have experimentally studied the dependence of Brownian and Neel relaxation times on ac and dc magnetic field amplitude using ac susceptibility measurements in the frequency range between 2 Hz and 9 kHz for field amplitudes up to 9 mT. As samples, single-core iron oxide nanoparticles with core diameters between 20 nm and 30 nm were used either suspended in water-glycerol mixtures or immobilized by freeze-drying. The experimentally determined relaxation times are compared with theoretical models. It was found that the Neel relaxation time decays much faster with increasing field amplitude than the Brownian one. Whereas the dependence of the Brownian relaxation time on the ac and dc field amplitude can be well explained with existing theoretical models, a proper model for the dependence of the Neel relaxation time on ac field amplitude for particles with random distribution of easy axes is still lacking. The extrapolation of the measured relaxation times of the 25 nm core diameter particles to a 25 mT ac field with an empirical model predicts that the Brownian mechanism clearly co-determines the dynamics of magnetic nanoparticles in magnetic particle imaging applications, in agreement with magnetic particle spectroscopy data. |
