Nanocomposites and nanomaterials

Paramagnetic properties of nanocomposites based on polyamide with carbon fibers as fillers
Krasnovyd S.V.1, Konchits A.A.1, Shanina B.D.1,
 Burya A.I.2, Tomina A.-M.V. 2
1 Department of Optics and Spectroscopy, V. Lashkaryov Institute of Semiconductor Physics of the NAS of Ukraine. Prospect Nauki, 41, Kyiv-03028, Ukraine. 
E-mail: sergkrasnovyd88@gmail.com
2 Department of Condensed Matter Physics, Dniprovsk State Technical University, Dneprostroevskaya str., 2, Kamenskoe-51918, Ukraine.

Among the many composite materials, one of the most widely used are composites containing carbon fibers (CFs) [1]. In CFs, crystallites of turbostratic graphite form layers with a length of several microns and a thickness of the order of nanometers.
In this work, we studied the ferro- and paramagnetic properties of carbon fibers of the Ural-24 type and their composites based on aromatic polyamide Phenilon C-2. It was established that the line of electron spin resonance (ESR) of the CFs bundles has an asymmetric, so-called Dyson shape, characteristic of EPR signals of conduction electrons with parameters: g=2.0034; Bpp=2.07 mT; R=50, where R=TD/T2; TD is the electron diffusion time through the skin layer, T2 is the electron spin relaxation time. In Phenylon C-2/CFs nanocomposites, the ESR spectrum is complicated by superparamagnetic and ferromagnetic signals due to the presence of micro- and nanoparticles of iron oxides as a component of the technological process. The ESR line width of the CFs in the composite increases up to Bpp=9.2 mT due to the inhomogeneous line broadening because of the distribution features of fibers and their interaction with matrix.
Strong non-resonant microwave absorption (NMP) is observed in CFs samples and composites due to the semiconductor nature of the conductivity of CFs, the free electrons of which absorb a wide spectrum of radio waves. In powdered samples of composites, the magnitude of the NMP effect strongly depends on the density of particles in volume of sample, which affects the electrical contact between them.

1.	Dresselhaus M. S., Dresselhaus G., Sugihara K., Spain L., Goldberg H. A. Graphite Fibers and Filaments // Springer-Verlag, 1988, 382 p.