Engineering Magnetic Properties of Ni Nanoparticles by Non-Magnetic Cores

Abstract

This work focuses on the magnetism-control study of nickel (Ni) nanoparticles (NPs) with nonmagnetic cores of noble metals (M = Ag, Au). Monodispersed M NPs used as templates were synthesized by reducing their salt with a weak reductant;oleylamine (OA). The OA acted as surfactant and non-coordinating reagent in the preparation of Ni NPs with a narrow size distribution. Then Ni atoms were controlled to grow upon the M NPs by controlling the decomposition of nickel acetylacetonate in OA. The as-prepared M and core/shell M/Ni NPs exhibit spherical shape, as characterized by transmission electron microscopy. The systematic study indicated that the Ni shell exhibits face-centered cubic crystal structure and is relatively stable in air. The hydrophobic OA molecules on the surface could be exchanged by hydrophilic imidazole to make the samples watersoluble. Magnetic study of core/shell NPs indicated that their blocking temperatures could be tuned by modulating either core size or shell thickness. The novel magnetic properties of the core/shell structured NPs are introduced by the size effect, exchange interaction, and reduced magnetic ordering. The novel core/shell M/Ni NPs are expected to have a significant potential for biomolecule separation, magnetic imaging, and optoelectronics.

Size‐, Shape‐ and Composition‐Dependent Alloying Ability of Bimetallic Nanoparticles

“…The referred data are from: solid circles, [19] solid squares, [20] solid triangles, [21] solid prism, [41] open squares, [42] open circles [43] and open triangles. [44] ChemPhysChem For large sizes of the Cu-Ag system, the Ag-rich alloys have a much broader alloying range compared to Cu-rich alloys. When the size reaches 5 nm, it is impossible for Cu-rich particles to form disordered alloys.…”

Mechanical activation on aluminothermic reduction and magnetic properties of NiO powders

“…This could be attributed to the contribution from various anisotropies such as magnetocrystalline anisotropy, shape anisotropy, strain anisotropy and exchange anisotropy for these fine nanosized Ni in nanocomposites prepared by ball milling process. Zhang et al [46] also reported size dependent enhanced K eff of the Ni nanoparticles in the range between 1.2 × 10 4 J m −3 and 6 × 10 4 J m . High values of K eff have also been reported in other nanocrystalline system [50] prepared by mechanical alloying process.…”

“…It may be noted that the milled NiO-Al powders exhibit RTFM despite having the average size of D Ni in the range below 25 nm, which is significantly below the critical size (~34 nm) of spherical Ni particles for single domain behavior at RT [44]. Hence, Ni nanoparticles will be of single domain but prone to thermal fluctuations [45,46]. Therefore, the obtained RTFM in the presently investigated samples can be correlated to one or more of the following several origins: (i) The milled powder exhibits quite irregular morphology (see figure 4) and hence the shape anisotropy could play a key role.…”

“…(iii) Surface anisotropy of the nanoparticles may also play an important role [45,47]. (iv) When the FM nanoparticles are embedded in an AFM matrix, an additional uniaxial type anisotropy is also introduced to the nanoparticles [46,48]. In order to analyze the effective magn etic anisotropy in the milled NiO-Al powders, we have fitted IM curves using law of approach of the magnetization to satur ation (LAS) as defined in equation (1) ⎜…”

Preparation and Characterization of Conductive SiO2-Polyaniline Core-Shell Nanoparticles

“…Due to diverse structures and properties, the core-shell nanoparticles have wide applications in various fields such as surface-enhanced Raman scattering, photonic crystals, catalysis, nano-electronic devices, and biochemical sensor [1]- [7].Among the various core-shell nanoparticles, the fabrication of inorganic nanoparticles coated with the shell of polymers has attracted increasing attention as new materials because of their novel mechanical, electrical, and optical properties [8]- [9]. Characteristics of the hybrid colloids can be adjusted through the functionality of polymer moieties.…”