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Anisotropic superparamagnetic resonance of Co nanoparticles in nanoporous carbon

Vladimir S. Yefanov 2Sergey P. Kolesnik 2Alexander M. Danishevskii 1V B. Shuman 1D A. Kurdjukov 1S K. Gordeev 3Andrey A. Konchits 2

1. Ioffe Physico-Technical Institute (Ioffe), Polytechnicheskaya, 26, Saint-Petersburg 194021, Russian Federation
2. V.Lashkaryov Institute of Semiconductor Physics NAS Ukraine (ISP), Nauky prosp., Kyiv 03028, Ukraine
3. Central Science Research Institute for Matherials, Saint-Petersburg, Russian Federation

Abstract


Here, we report on the synthesis and magnetic resonance study of Co nanoparticles, encapsulated in nanoporous carbon (NPC). NPC powder samples were prepared from carbide Mo2C using the chemical removal of non-carbon carbide forming atoms. Size of nanopores was estimated as 1-7 nm. Impregnation of Co into was done from CoCl2 during 48 hours at T = 980 C.
At room temperature the as grown powder samples of NPC: Co show magnetoresonance responce ( ν=9.3 GHz) represented by two superposed lines, a broad and a narrow ones, with effective g-factor close to g=2.0.
The sample with separated granules of NPC: Co demonstrate only one almost symmetric line of absorption (ΔHpp = 340 G at T=300 K) determined by magnetic response of superparamagnetic Co particles above their blocking temperature. The resonance field corresponds to g-factor of g=2.22, which is close to the one of Co. As temperature decrease, parameters of the line change sufficiently being an evidence for a spectrum anisotropy. Such anisotropy could be interpreted as anisotropic superparamagnetic resonance, taking into account both anisotropy energy of the nanoparticles and effective magnetization of the non-spherical form of nanoparticles in a disordered system. Using the value of blocking temperature (about 70 K) estimated from our measurements, mean size of Co nanoparticles was obtained as 5 nm.

 

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Presentation: poster at E-MRS Fall Meeting 2004, Symposium I, by Vladimir S. Yefanov
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-04-30 15:19
Revised:   2009-06-08 12:55