NixPt1−x is the missing link in the series of magnetic alloy particles. We report here on the first high‐quality synthesis of this nanomaterial. Although the chemistry of the Fe, Co, and Ni compounds is usually similar, distinctive differences are found in the nucleation, growth, and shape control of the respective nanoparticles, and first magnetic measurements are presented. The image shows star‐shaped agglomerates of nanoparticles.
To date, no large-scale preparative method for arrays of nanotube enables the experimentalist to arbitrarily define changes in the tubes' diameter along their length. To this goal, we start with anodic alumina substrates displaying controlled modulations in pore diameter obtained by alternating "mild" and "hard" electrochemical etching conditions. We then utilize atomic layer deposition (ALD) to coat the internal pore walls with conformal layers of an oxide. Ferromagnetic Fe(3)O(4) tubes of 10 nm wall thickness and 10-30 microm in length are thus prepared, which replicate the modulated silhouette of the template. Their magnetic properties strongly depend on the presence of diameter modulations. Introducing one or several very short segments of large diameter (150 nm) into an otherwise thin tube (70 nm diameter) brings its initially large coercive field down to a value close to the case of a homogeneously thick tube. Theoretical modeling emphasizes the major influence of the magnetostatic interactions between neighboring tubes. They are enhanced locally at the sites of diameter modulations, which directly translates into a reduction in coercive field.
We report on the experimental and theoretical investigation of the magnetization reversal in magnetic nanotubes that have been synthesized by a combination of glancing angle and atomic layer deposition. Using superconducting quantum interference device magnetometry the angular dependence of the coercive fields is determined and reveals a nonmonotonic behavior. Analytical calculations predict the crossover between two magnetization reversal modes, namely, the movement of different types of domain boundaries (vortex wall and transverse wall). This transition, already known in the geometrical dependences of the magnetization reversal in various nanotubes, is found within one type of tube in the angular dependence and is experimentally confirmed in this work.
Nickel oxide films obtained from nickelocene and ozone by atomic layer deposition at 230°C are substoichiometric, but have the crystal structure of NiO. Oxygen can be driven out of the solid by annealing under inert atmosphere, or added into it via aerobic annealing.
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.
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