Europhys. Lett.
Volume 74, Number 5, June 2006
Page(s) 903 - 908
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 03 May 2006
Europhys. Lett., 74 (5), pp. 903-908 (2006)
DOI: 10.1209/epl/i2005-10586-y

The effect of nano-sized superparamagnetic particles on the dielectric constant of polyimide

J. H. Kang1, C. E. Park1 and Y. H. Jeong2, 3

1  Department of Chemical Engineering and Polymer Research Institute Pohang University of Science and Technology - Pohang, 790-784, S. Korea
2  Department of Physics and electron Spin Science Center Pohang University of Science and Technology - Pohang, 790-784, S. Korea
3  Department of Physics and Astronomy, Michigan State University E. Lansing, MI 48824, USA

received 23 December 2005; accepted in final form 5 April 2006
published online 3 May 2006

We propose that dynamically induced internal fields be utilized in obtaining materials with low dielectric constant at high frequencies. We also demonstrate the validity of the proposal by measuring the effective dielectric constant of polyimide dispersed with nano-sized $\chem{Ni_{0.6}Zn_{0.4}Fe_2O_4}$ particles. The dielectric constant of a polyimide composite measured at $1\un{MHz}$ increases as a function of $\chem{Ni_{0.6}Zn_{0.4}Fe_2O_4}$ contents when the diameter of the embedded particles is approximately $20\un{nm}$. On the other hand, the measured dielectric constant of a composite containing superparamagnetic particles of diameter approximately $6\un{nm}$ showed much smaller value than that of pure polyimide. These contrasting behaviors indicate that the induced internal fields are in operation, in reducing the dielectric constant, for a material with superparamagnetic particles.

77.22.Ch - Permittivity (dielectric function).
71.20.Rv - Polymers and organic compounds.
77.55.+f - Dielectric thin films.

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