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Second-order-like cluster-monomer transition within magnetic fluids and its impact upon the magnetic susceptibility

Jing Zhong1, Qing Xiang1, Letícia O Massa2, Fanyao Qu2, Paulo C Morais2 and Wenzhong Liu1*

Author Affiliations

1 Department of Control Science and Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China

2 Instituto de Física, Núcleo de Física Aplicada, Universidade de Brasília, Brasília DF, 70910-900, Brazil

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Nanoscale Research Letters 2012, 7:167  doi:10.1186/1556-276X-7-167

Published: 5 March 2012


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.

magnetic fluid; inverse initial susceptibility; cluster disruption; critical temperature; Langevin function