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Proceedings ArticleDOI

Phase stability and magnetic properties of Ni-nanoparticles prepared by chemical reduction methods

05 Nov 2020-Vol. 2265, Iss: 1, pp 030534
TL;DR: In this article, a comparative study of Ni nanoparticles synthesized by NaBH4 reduction method (SBR) and Polyol process (PP) has been carried out.
Abstract: A comparative study of structure, stability and magnetic properties of Ni nanoparticles (NPs) synthesized by NaBH4 reduction method (SBR) and Polyol process (PP) has been carried out. Temperature and field dependence magnetization measurements suggest that 600 °C air annealed for 1 hour samples exhibit weak and strong magnetic properties for samples prepared by PP and SBR methods respectively. From the structural and magnetic measurements we conclude that Ni particles prepared by SBR and annealed at 600 °C air develops in to core-shell structure NPs while PP NPs under similar conditions show heterogeneous magnetic (Ni/NiO) behavior.
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Journal ArticleDOI
TL;DR: In this paper, the magnetic properties of sol-gel prepared nickel oxide nanoparticles of different sizes were studied and various measurements such as frequency, field, and temperature dependence of ac susceptibility, temperature and field dependence of dc magnetization, and time decay of thermoremanent magnetization.
Abstract: We present a detailed study of the magnetic properties of sol-gel prepared nickel oxide nanoparticles of different sizes. We report various measurements such as frequency, field, and temperature dependence of ac susceptibility, temperature and field dependence of dc magnetization, and time decay of thermoremanent magnetization. Our results and analysis show that the system behaves as a spin glass.

223 citations

Journal ArticleDOI
TL;DR: The outstanding glucose sensing performance should be attributed to the unique 3D hierarchical porous superstructure of the composite, especially for its enhanced electron-transfer kinetic properties.
Abstract: The 3D NiO hollow sphere/reduced graphene oxide (rGO) composite was synthesized according to the coordinating etching and precipitating process by using Cu2O nanosphere/graphene oxide (GO) composite as template. The morphology, structure, and composition of the materials were characterized by SEM, TEM, HRTEM, XPS, and Raman spectra, and the electrochemical properties were studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and amperometry. Moreover, the electrochemical activity of the composite materials with different morphologies were also investigated, which indicating a better combination of the NiO hollow sphere and the rGO. Used as glucose sensing material, the 3D NiO hollow sphere/rGO composite modified electrode exhibits high sensitivity of ~2.04 mA mM−1 cm−2, quick response time of less than 5 s, good stability, selectivity, and reproducibility. Its application for the detection of glucose in human blood serum sample shows acceptable recovery and R.S.D. values. The outstanding glucose sensing performance should be attributed to the unique 3D hierarchical porous superstructure of the composite, especially for its enhanced electron-transfer kinetic properties.

151 citations

Journal ArticleDOI
TL;DR: The functionalized Au and M/Au nanoparticles are shown to exhibit the desired functional properties for the detection of SERS signals in the magnetically separated reaction products.
Abstract: The ability to create bio-functional nanoprobes for the detection of biological reactivity is important for developing bioassay and diagnostic methods. This paper describes the findings of an investigation of the surface functionalization of gold (Au) and magnetic nanoparticles coated with gold shells (M/Au) by proteins and spectroscopic labels for the creation of nanoprobes for use in surface enhanced Raman scattering (SERS) assays. Highly monodispersed Au nanoparticles and M/Au nanoparticles with two types of magnetic nanoparticle cores (Fe2O3 and MnZn ferrite) were studied as model systems for the bio-functionalization and Raman labeling. Comparison of the SERS intensities obtained with different particle sizes (30?100?nm) and samples in solution versus on solid substrates have revealed important information about the manipulation of the SERS signals. In contrast to the salt-induced uncontrollable and irreversible aggregation of nanoparticles, the ability to use a centrifugation method to control the formation of stable small clustering sizes of nanoparticles was shown to enhance SERS intensities for samples in solution as compared with samples on solid substrates. A simple method for labeling protein-capped Au nanoparticles with Raman-active molecules was also described. The functionalized Au and M/Au nanoparticles are shown to exhibit the desired functional properties for the detection of SERS signals in the magnetically separated reaction products. These results are discussed in terms of the interparticle distance dependence of 'hot-spot' SERS sites and the delineation of the parameters for controlling the core?shell reactivity of the magnetic functional nanocomposite materials in bio-separation and spectroscopic probing.

79 citations

Journal ArticleDOI
TL;DR: In this article, the use of high-temperature oxidation and reduction to produce highly crystalline nanoparticles of Ni and NiO was described, and it was shown that the Ni nanoparticles are much more resistant to oxidation than the original Ni powder, perhaps due to the relative crystalline perfection of the former.
Abstract: We describe here the use of high-temperature oxidation and reduction to produce highly crystalline nanoparticles of Ni and NiO. Starting with an amorphous Ni powder, we demonstrate that oxidation at $900\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ produces faceted NiO nanocrystals with sizes ranging from 20 to 60 nm. High-resolution transmission electron microscopy measurements indicate near-perfect atomic order, truncated by (200) surfaces. Magnetization measurements reveal that the N\'eel temperature of these NiO nanoparticles is 480 K, substantially reduced by finite-size effects from the bulk value of 523 K. The magnetization of these faceted NiO nanoparticles does not saturate in fields as large as 14 T while a loop offset is observed which increases from 1000 Oe at 300 K to its maximum value of 3500 Oe at 50 K. We have used high-temperature reduction to transform the faceted NiO nanoparticles into highly ordered Ni nanoparticles, with a Curie temperature of 720 K and blocking temperatures in excess of 350 K. Subsequent efforts to reoxidize these Ni nanoparticles into the core-shell morphology found that the Ni nanoparticles are much more resistant to oxidation than the original Ni powder, perhaps due to the relative crystalline perfection of the former. At $800\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$, an unusual surface roughening and subsequent instability was observed, where 50-nm-diameter NiO rods grow from the Ni surfaces. We have demonstrated that high-temperature oxidation and reduction in Ni and NiO are both reversible to some extent and are highly effective for creating the highly crystalline nanomaterials required for applications such as exchange-bias devices.

69 citations

Journal ArticleDOI
TL;DR: Two significant indexes for the dipolar interaction n and multi-anisotropic barrier β derived from the dynamic magnetization are proposed, which provide a unified picture of the exchange bias mechanism and insight into the influence of the cooling field.
Abstract: We review the phenomenology of the exchange bias and its related effects in core–shell nanocrystals. The static and dynamic properties of the magnetization for ferromagnetic Ni-core and antiferromagnetic NiO-shell cluster glassy nanoparticles are examined, along with the pinning–depinning process, through the measurement of the conventional exchange bias, and associated with different cooling fields and particle sizes. Two significant indexes for the dipolar interaction n and multi-anisotropic barrier β derived from the dynamic magnetization are proposed, which provide a unified picture of the exchange bias mechanism and insight into the influence of the cooling field.

28 citations