New synthetic methodology and magnetic properties of fcc Co-Ni nanostructured alloys embedded in KIT-6 matrix
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Magnetic characteristics of nanocrystalline CoNi alloy materials embedded in silica matrix (KIT-6) have been investigated. CoNi alloys with different loading (4–12 wt%) were synthesized via a novel chemical reduction route. The materials are characterized by UV–VIS, IR, powder x-ray diffraction (XRD), transmission electron microscopy (TEM) and studied for their adsorption–desorption and magnetic properties. CoNi alloys crystallize in pure fcc phase with lattice parameters (a) and crystallite sizes in the range of 3.53(62)–3.54(62) Å and 13.6(61)–16.3(61) nm, respectively. TEM microscopy studies reveal nanocrystalline nature of the materials. Enhancement of magnetic moment with the increase in loading wt% for CoNi alloys embedded in silica matrix is observed. The values of coercivity tend to decrease after dispersion in silica matrix and thereafter increase with increasing loading wt% of various CoNi loaded samples. The observed magnetic properties have been explained on the basis of size, surface effects, and dipolar interactions. I. INTRODUCTION
Recently, various non-conventional magnetic systems are being explored for their interesting magnetic characteristics.1,2 Some of them include diluted magnetic systems with unusual magnetic properties which may be of technological interest.2,3 In this regard, magnetic alloy nanoparticles (nps) dispersed in porous matrix have attracted great interest in scientific research because of their unique physical properties.4 The functional properties are derived from the synthesis and processing parameters; such as: controlled nucleation, growth of nanoparticles within the silica matrix, heat treatment using different inert atmosphere etc. These materials have potential applications in various fields; such as: catalysis,5 biomedical,6 magnetic recording media,7 microwave absorption materials8 etc. Alloy nps embedded in silica matrix show altered magnetic properties (MS, HC, Keff etc.). The values of the saturation magnetizations (MS) can be different from that of the bulk materials.9,10 Co, Ni, and their alloys nanoclusters in silica host show an enhancement in the magnetic moment and decrease in coercivity due to the superparamagnetic behavior.11 Significant changes in effective anisotropy constant (Keff) are also reported for metal/alloy nanostructures.9 These variations in the magnetic properties of nanomaterials embedded in silica matrix have already been attributed to several aspects such as high surface area to volume ratio, electronic Contributing Editor: Michael E. McHenry a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.255
structure, interaction between nanomaterials and matrix, or interparticle interactions.10,12,13 To control size, dispersion, stability, and interparticle interactions among nps, nano-composites of alloys (e.g., Co–Ni, Ni–Cu, Co–Cu, Fe–Co etc.) in silica matrix have been synthesized by various synthesis techniques such as sol–gel method,10 high temperature hydrogen reduction method,14 ion implantation me
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