The influence of oleylamine (OLA) concentration on the crystallography, morphology, surface chemistry, chemical bonding, and magnetic properties of solvothermal synthesized CoFe2O4 (CFO) nanoparticles (NPs) has been thoroughly investigated. Varying OLA concentration (0.01–0.1 M) resulted in the formation of cubic spinel-structured CoFe2O4 NPs in the size-range of 20–14 (±1) nm. The Fourier transform spectroscopic analyses performed confirmed the OLA binding to the CFO NPs. The thermogravimetric measurements revealed monolayer and multilayer coating of OLA on CFO NPs, which were further supported by the small-angle X-ray scattering measurements. The magnetic measurements indicated that the maximum saturation (MS) and remanent (Mr) magnetization decreased with increasing OLA concentration. The ratio of maximum dipolar field (Hdip), coercivity (HC), and exchanged bias field (Hex) (at 10 K) to the average crystallite size (Dxrd), i.e., (Hdip/Dxrd), (HC/Dxrd), and (Hex/Dxrd), increased linearly with OLA concentration, indicating that OLA concurrently controls the particle size and interparticle interaction among the CFO NPs. The results and analyses demonstrate that the OLA-mediated synthesis allowed for modification of the structural and magnetic properties of CFO NPs, which could readily find potential application in electronics and biomedicine.
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DNA‐ and Field‐Mediated Assembly of Magnetic Nanoparticles into High‐Aspect Ratio Crystals
Under an applied magnetic field, superparamagnetic Fe3O4nanoparticles with complementary DNA strands assemble into crystalline, pseudo‐1D elongated superlattice structures. The assembly process is driven through a combination of DNA hybridization and particle dipolar coupling, a property dependent on particle composition, size, and interparticle distance. The DNA controls interparticle distance and crystal symmetry, while the magnetic field leads to anisotropic crystal growth. Increasing the dipole interaction between particles by increasing particle size or external field strength leads to a preference for a particular crystal morphology (e.g., rhombic dodecahedra, stacked clusters, and smooth rods). Molecular dynamics simulations show that an understanding of both DNA hybridization energetic and magnetic interactions is required to predict the resulting crystal morphology. Taken together, the data show that applied magnetic fields with magnetic nanoparticles can be deliberately used to access nanostructures beyond what is possible with DNA hybridization alone.
more » « less- NSF-PAR ID:
- 10458633
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 32
- Issue:
- 4
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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