Abstract
The low-field (below 5 Oe) ac and dc magnetic response of a magnetic fluid [MF] sample in the range of 305 to 360 K and 410 to 455 K was experimentally and theoretically investigated. We found a systematic deviation of Curie's law, which predicts a linear temperature dependence of inverse initial susceptibility in the range of our investigation. This finding, as we hypothesized, is due to the onset of a second-order-like cluster-to-monomer transition with a critical exponent which is equal to 0.50. The susceptibility data were well fitted by a modified Langevin function, in which cluster dissociation into monomers, at the critical temperature [T*], was included. In the ac experiments, we found that T* was reducing from 381.8 to 380.4 K as the frequency of the applied field increases from 123 to 173 Hz. In addition, our ac experiments confirm that only monomers respond for the magnetic behavior of the MF sample above T*. Furthermore, our Monte Carlo simulation and analytical results support the hypothesis of a thermal-assisted dissociation of chain-like structures.PACS: 75.75.-C; 75.30.Kz; 75.30.Cr.
Highlights
The interest in magnetic fluids [MFs] has increased enormously in the last decade, due to the opportunities they provide for applications in the medical field [1,2,3,4,5,6,7]
MFs have been used as an excellent material platform for the development of magnetic immunoassay [1,2], contrast agents for magnetic resonance imaging [3,4], and material devices for magnetohyperthermia [5,6,7]
We report the unusual superlinear deviation in the temperature dependence of the inverse initial magnetic susceptibility in a magnetite-based (Fe3O4) MF sample in the temperature range of 305 to 360 K
Summary
The interest in magnetic fluids [MFs] has increased enormously in the last decade, due to the opportunities they provide for applications in the medical field [1,2,3,4,5,6,7]. The design of nanosized magnetic particles, taking into account the maximization of the materials’ response in terms of their use for diagnosis, imaging, and therapy, requires the knowledge of the temperature dependence of the magnetic susceptibility under the action of applied dc and ac fields. In this context, the widely accepted concept is a linear relationship between the inverse initial magnetic susceptibility (1/c) and the temperature (T), which is accounted for by the first-order Langevin function. To understand the underlying physics of this nonlinearity in magnetization, a more complete physical model is highly demanded
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