Correlating the electronic structure and magnetic response with the morphology and crystal structure of the same single ferromagnetic nanoparticle has been up to now an unresolved challenge. Here, we present measurements of the element-specific electronic structure and magnetic response as a function of magnetic field amplitude and orientation for chemically synthesized single Fe nanocubes with 18 nm edge length. Magnetic states and interactions of monomers, dimers, and trimers are analyzed by X-ray photoemission electron microscopy for different particle arrangements. The element-specific electronic structure can be probed and correlated with the changes of magnetic properties. This approach opens new possibilities for a deeper understanding of the collective response of magnetic nanohybrids in multifunctional materials and in nanomagnetic colloidal suspensions used in biomedical and engineering technologies.
The experimental yield of ZnO nanocrystals decreases drastically with increasing reactor temperature in a typical chemical vapor synthesis (CVS) of ZnO nanocrystals from diethylzinc. A novel CVS set-up -a microwave plasma combined with a hotwall zone -is described to minimize the loss of particles at higher reactor temperatures. The powder samples have been characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). It is observed that the synthesis set-up and reaction temperature have substantial influence not only on yield but also on crystallite size and crystallinity of the pure wurtzite-type ZnO nanocrystals. The lattice constants of ZnO nanocrystals increase with decreasing crystallite size. Defect densities (twin and stacking faults), as well as microstrain, decrease with increasing reactor temperature, whereas crystallinity increases.
The Spin-resolved Photoelectron Emission Microscope (SPEEM) is a permanently installed setup at Helmholtz-Zentrum Berlin (HZB). Due to its specific contrast it is mainly used for magnetic imaging and micro-spectroscopy with quantitative analysis. A crucial point in magnetic imaging is the application of magnetic fields. Many experiments require observation of magnetic responses or the preparation of a certain magnetic state during the measurement. We present a dedicated magnetic sample holder combining magnetic field during imaging with additional temperature control. This setup enables SPEEM to measure magnetization curves of individual Fe nanocubes (18 nm) 3 in size. If additionally alternating magnetic fields are applied we can image the local magnetic AC susceptibility (AC) as a function of temperature. The latter is ideally suited to visualize local variations of the Curie temperature (T C) in nanoand microstructures.
FePt nanoparticles are promising materials for high-density magnetic data storage media [1] and bio-medical applications such as drug-targeting and hyperthermia [2]. To understand their magnetic properties [3] it is essential to get insights into the lattice structure of isolated nanoparticles which influence the magnetic behavior. Typically, lattice fringes are observed with high-resolution transmission electron microscopy (HR-TEM). In this case delocalization effects disturb imaging of the lattice structure in particular if 2 to 6 nm small nanoparticles are involved. Therefore, FePt nanocrystals were investigated by reconstructing amplitude and phase of the scattered electron wave from a focal series of HRTEM images, which can produce delocalization free and direct images of the crystal structure [4]. The formation of 5-fold twinned structures of 3 to 7 nm face-centered cubic FePt nanocrystals is investigated that were grown from a colloidal solution [1]. The results are compared with abinitio density functional (DFT) calculations of FePt particles with a diameter of larger than 2 nm. Image simulations were performed with the Accelrys Cerius 2 software package (Version 4.6). Good agreement between the ab-initio calculations and the experimental data is found.
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