Nanocomposites and nanomaterials

Magneto-transport properties of nanographite structures obtained by different methods 
Syvolozhskyi O. A., Ovsiienko I. V., Len T. A., Matzui L. Yu., Marinin O. D.
Taras Shevchenko National University of Kyiv, 01601, Kyiv, Volodymyrska st. 64/13, Department of Physics
E-mail: mail.olexiy@gmail.com

The presented work is devoted to questions of evolution of magneto-transport properties of nanographites with different structure perfection. The specimens of nanographite were obtained by methods of chemical treatment (1.5 М solution of KMnO4 in 20% H2SO4 on the sand bath) and ultra-sonic treatment in different chemical environments (water, ethanol, acetone) of source thermoexfoliated graphite (TEG). The structure of obtained nanographite specimens was investigated by electron microscopy and Raman spectroscopy methods. It is revealed, that the chemical treatment of source TEG lets to get the planar defective graphenelike sheets with small number of graphite. The lateral crystalline size for this nanographite does not exceed the 5 nm. The use of sonication for dispersion of source TEG results in the formation of nanographites with a weekly expressed defects in graphite layers with lateral crystalline size ~ 40 nm.
The Fig. 1 presents the typical field dependences of magnetoresistance (/(B)) for bulk specimens of chemically treated (a) and sonicated (b) nanographites.
a)	b)	As can be seen from Fig. the magneto-resistance for chemically treated nano-graphite is quadratic and negative at low temperature. This negative magnetoresistance is explained in terms of week localization effect.	
Fig. 1. Dependences /(B) for chemically treated (a) and sonicated (b) nanographites		
For sonicated nanographites magnetiresistance is positive and independent from temperature. The linear dependence of magnetoresistance from magnetic field is observed. This effect is satisfactorily described in the terms of Abrikosov model of quantum linear magnetoresistance.