CitationHighly Uniformly sized and shaped iron oxide nanoparticles with a mean size of 25 nm were synthesized via decomposition of ironoleate. High resolution transmission electron microscopy and Mössbauer spectroscopy investigations revealed that the particles are spheres primarily composed of Fe 3 O 4 with a small fraction of FeO. From Mössbauer and static magnetization measurements, it was deduced that the particles are superparamagnetic at room temperature. The hydrophobic particles were successfully transferred into water via PEGylation using nitrodopamine as an anchoring group. IR spectroscopy and thermogravimetric analysis showed the success and efficiency of the phase transfer reaction. After the PEGylation, the particles retained monodisperse and their magnetic core remained intact as proven by photon cross-correlation spectrocopy, ac susceptibility, and transmission electron microscopy. The particle aqueous suspensions revealed an excellent water stability over a month of monitoring and also against temperature up to 40 • C. The particles exhibited a moderate cytotoxic effect on in vitro cultured bone marrow-derived macrophages and no release of inflammatory or anti-inflammatory cytokines. The PEGylated particles were functionalized with Herceptin antibodies via a conjugation chemistry, their response to a rotating magnetic field was studied using a fluxgate-based setup and was compared with the one recorded for hydrophobic and PEGylated particles. The particle phase lag rose after labeling with Herceptin, indicating the successful conjugation of Herceptin antibodies to the particles.
Permalloy (Ni80Fe20) is broadly used to prepare magnetic nanostructures for high-frequency experiments where the magnetization is either excited by electrical currents or magnetic fields. Detailed knowledge of the material properties is mandatory for thorough understanding its magnetization dynamics. In this work, thin Permalloy films are grown by dc-magnetron sputtering on heated substrates and by thermal evaporation with subsequent annealing. The specific resistance is determined by van der Pauw methods. Point-contact Andreev reflection is employed to determine the spin polarization of the films. The topography is imaged by atomic-force microscopy, and the magnetic microstructure by magnetic-force microscopy. Transmission-electron microscopy and transmission-electron diffraction are performed to determine atomic composition, crystal structure, and morphology. From ferromagnetic resonance absorption spectra the saturation magnetization, the anisotropy, and the Gilbert damping parameter are determined. Coercive fields and anisotropy are measured by magneto-optical Kerr magnetometry. The sum of the findings enables optimization of Permalloy for spintronic experiments.
Domain walls in curved Permalloy (Ni80Fe20) nanowires are depinned by nanosecond current pulses and magnetic fields. A significant dependence of the depinning probability on the pulse length is observed. We measure an oscillatory dependence with a characteristic frequency of 270 MHz. The quality of the Permalloy used for the nanowires is crucial for efficient domain-wall depinning. By sputtering Permalloy on heated substrates we are able to considerably decrease the specific resistance that is found to directly correspond to the depinning field of the domain wall.
We present point-contact Andreev reflection (PCAR) spectroscopy on Permalloy (Ni80Fe20) and on the half-metallic Heusler alloy Ni2MnIn. The thin Permalloy films are deposited on Si, the Ni2MnIn films on Si as well as on in situ cleaved (110) surfaces of InAs. A highly conductive layer under the ferromagnetic film almost eliminates a series resistance and thus facilitates the determination of the spin polarization from the differential conductance curves. We obtain a spin polarization of Permalloy of 35%. The spin polarization of Ni2MnIn depends on the substrate, presumably due to the growth of different crystal structures. It is shown that the surface sensitive PCAR spectroscopy cannot determine the spin polarization of the bulk material of half-metals where the degree of spin polarization strongly depends on the crystal structure.
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