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Evidence of Formation of Co_{x}Cu_{1-x} Nanoparticles with Core-Shell Structure

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Dhara S., Chowdhury R., Bandyopadhyay B.

Acta Physica Polonica A

2015

vol. 128

issue 4

533-535

We have prepared Co_{x}Cu_{1-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 (H_{C}) 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.

Effect of Vanadium Substitution of Cobalt in NdCo₂Si₂

100%

Chowdhury R., Dhara S., Bandyopadhyay B.

Acta Physica Polonica A

2015

vol. 128

issue 4

530-532

In NdCo₂Si₂, partial substitution of Co by V having a larger atomic radius results in negative pressure affecting the magnetic properties of the compound. The samples Nd(Co_{1-x}V_{x})₂Si₂ (x=0, 0.20, 0.35) have been prepared and characterized using X-ray diffraction. The parent compound NdCo₂Si₂ is antiferromagnetic with T_{N} of 34 K whereas the temperature dependence of inverse susceptibility in the doped samples show ferrimagnetic behaviour below 45 K. From the magnetic field dependence of magnetization and the coercive fields obtained from hysteresis loops, the doped samples exhibit ferromagnetism below ≈ 20 K. The specific heat studies compare the magnetic transitions in the parent and doped samples. Nd(Co_{0.65}V_{0.35})₂Si₂ shows a magnetoresistance of 15% at 4 K.

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2 Acta Physica Polonica A

2 2015

2 Bandyopadhyay B.

2 Chowdhury R.

2 Dhara S.

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Evidence of Formation of Co_{x}Cu_{1-x} Nanoparticles with Core-Shell Structure

Effect of Vanadium Substitution of Cobalt in NdCo₂Si₂