Nanocomposites and nanomaterials
Magnetoresistance of modified by Cobalt Carbon nanotubes
Shpylka D.O.1, Ovsiienko I.V.1, Len T.A.1, 
Matzui L.Yu.1, Trukhanov Alex.V2
1Taras Shevchenko National University of Kyiv, Department of Physics, 64/13 Volodymyrska st., 01601, Kyiv, Ukraine
E-mail: denys8600@ukr.net
2Scientific Practical Materials Research Centre of NAS of Belarus, Minsk, Belarus 

The work presents the results of investigations of magnetoresistance of modified by Cobalt multiwall carbon nanotubes (MWCNTs) at different mutual orientation between the direction of the magnetic field and the direction of current through MWCNTs specimen. The modification of MWCNTs with cobalt (30% mass) has been performed by the method of metal reduction from aqueous salt solution. According to structural and phase investigations modified MWCNTs contain cobalt (ferromagnetic phase) and cobalt oxide (CoO) (antiferromagnetic phase with Neel temperature TN = 291 K) particles up to 3 nm in size. Cobalt and cobalt oxide particles are distributed in internal cavity of MWCNTs and at the ends of tubes. For magnetoresistance measurements MWCNTs bulk specimens have been prepared by cold compacting of nanotubes with PVA as binder (25% mass). The resistance has been measured in the temperature interval from 4.2 K to 293 K and in the magnetic fields up to 2.2 T. 
Figure presents the field dependences of magnetoresistance /0(B) for bulk specimens of modified MWCNTs at room temperature and T = 4.2 K at parallel mutual orientation of the magnetic field and current through specimen. 
a	
b	As can be seen from the Figure in dependence /0(B) there is a pronounced hysteresis that is symmetric with respect to the magnetic field. The coercive force (Bc) is ~ 0.09 T. This type of /0(B) dependence is characteristic for systems containing ferromagnetic and antiferromagnetic phases and is associated with the realization of 	
Fig. /0(B) for modified MWCNTs at T = 293 K (a) and T = 4.2 K (b), B I. Arrows and numbers indicate the sequence of measurements		
the effect of the giant magnetoresistance due to exchange anisotropy that occurs between the layers of ferro- and antiferromagnets.