In this work, we have prepared nanosize-needles of mixed content (Co / Co oxide) using the sonochemical method for decomposition of metal complexes. In our research, we used cobalt carbonyl (Co2(CO)8) as the metal precursor. In the experiments, 2 g of carbonyl (5.8 mmol) were dissolved in 100 ml of deionized distilled water (sample 1) or in a water-alcohol (1:1 volume) mixture (sample 2). After this, 0.5 g of Poly-ethyleneglycole was added to the mixture. The resulting solution was treated with ultrasonic (Bandelin Sonopuls 3200, Ti-probe KE-76, amplitude 50%) for 40 min. The reaction mass was then centrifuged, and the resulting powders were studied. According to the TEM images, sample 1 contains nanosize-needles of about 19 nm in length and 5 nm in diameter which are congregated with each other into more complex web-like structures. Sample 2 also contains nanosize-needles (28 nm in length, 4 nm in diameter), however, along with spherical nanoparticles (7 nm in diameter). According to the XRD patterns, both the samples consist of polyethylene glycol, Co, and Co3O4. Magnetic measurements of the samples revealed their low blocking temperature (near 25 K°), which indicates that the samples have compound composition. ESR measurements displayed no signals from ions for sample 2 and a weak paramagnetic signal for sample 1. That indicates that both the samples are paramagnetic but display strong spin-lattice relaxation. Acknowledgements: this work has received partial financial support from the Russian Foundation for Basic Research (grant nos. 06-03-72031-MSTI, 07-03-00885, 07-08-00523, 08-03-00681, 08-08-90250), INTAS-05-1000008-7834, the grant of the President of the Russian Federation MK- 253.2007.3, Russian Science Support Foundation, ISTC nos. 3457, the Russian Academy of Sciences of the research programs.

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1. New nanocomposite materials with unique property combination