Evidence of Formation of CoxCu1-x Nanoparticles with Core-Shell Structure
S. Dhara, R. Roy Chowdhury and B. Bandyopadhyay
Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064, India
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We have prepared CoxCu1-x granular alloys with Co contents (x ≈ 0.01-0.30) by chemical reduction. Samples are characterized by X-ray diffraction and transmission electron microscopy yielding particles of mean diameter 8-20 nm formed in fcc phase. The branching in ZFC/FC magnetization behavior confirm superparamagnetism in the samples, characterized by blocking temperature distributions which represent variations in particle size and inhomogeneities of their chemical compositions. Magnetic field dependence of magnetization show hysteresis loops, and the magnetization at any temperature 4-300 K is a combination of ferromagnetism and superparamagnetism. The saturation moment of Co for the ferromagnetism part increases with the Co content. But the coercive fields (HC) and magnetic anisotropy of the particles do not vary with Co concentration. Annealed samples exhibit exchange bias in the range 20-150 Oe at 4 K. The results indicate formation of nanoparticles of CoCu alloy in a core-shell type structure with Co being concentrated near the core.

DOI: 10.12693/APhysPolA.128.533
PACS numbers: 75.75.Fk, 61.05.cp, 75.60.-d