RESUMEN
We present two new and complementary approaches to realize spatial resolution for ferromagnetic resonance (FMR) on the 100 nm-scale. Both experimental setups utilize lithographically fabricated micro-resonators. They offer a detection sensitivity that is increased by four orders of magnitude compared with resonator-based FMR. In the first setup, the magnetic properties are thermally modulated via the thermal near-field effect generated by the thermal probe of an atomic force microscope. In combination with lock-in detection of the absorbed microwave power in the micro-resonator, a spatial resolution of less than 100 nm is achieved. The second setup is a combination of a micro-resonator with a scanning transmission x-ray microscope (STXM). Here a conventional FMR is excited by the micro-resonator while focused x-rays are used for a time-resolved snap-shot detection of the FMR excitations via the x-ray magnetic circular dichroism effect. This technique allows a lateral resolution of nominally 35 nm given by the STXM. Both experimental setups combine the advantage of low-power FMR excitation in the linear regime with high spatial resolution to study single and coupled nanomagnets. As proof-of-principle experiments, two perpendicular magnetic micro-stripes (5 µm × 1 µm) were grown and their FMR excitations were investigated using both setups.
RESUMEN
Test structures for electromigration with defined grain boundary configurations can be fabricated using focused ion beam (FIB). We present a novel approach of combining epitaxial growth of Ag islands with FIB milling. Depending on the growth parameters, bi-crystalline Ag islands can be grown on Si(111) surfaces and can be structured into wires by FIB. To avoid doping effects of the used Ga FIB, silicon on insulator (SOI) substrates are used. By cutting through the device layer of the SOI substrate with deep trenches, the Ag wire can be electrically separated from the rest of the substrate. In this way, Ag wires with one isolated grain boundary of arbitrary direction can be assembled. Using scanning electron microscopy we demonstrate the feasibility of our approach.
RESUMEN
In this work we investigate the electrical transport properties and growth conditions of tungsten carbon (WC) and palladium carbon (PdC) nanostructures on Si substrates using a focused ion beam and scanning electron microscope. In situ energy dispersive x-ray (EDX) characterizations reveal that electron-beam-induced WC and PdC nanostructure depositions (EBID) show a lower metal concentration (below 3% atomic percentage) than in ion-beam-induced deposition (IBID) (above 20%). In the case of PdC the growth pattern and the Pd/C content were optimized by adjusting the deposition temperature of the precursor material. In situ measurements of the resistivity of the nanostructures as a function of thickness reveal a minimum at a thickness approximately 200 nm. The lowest resistivity obtained for the PdC and WC structures is two orders of magnitude higher than the corresponding bulk values for pure Pd and W. The EBID samples show a non-metallic behaviour due to the low metal content. The temperature and magnetic field dependence of the IBID structures reveal a behaviour similar to disordered or granular conductors. The upper critical field and critical current density of the WC structures were measured below the superconducting critical temperature of approximately 5 K.
RESUMEN
Conduction electrons in graphite are expected to have micrometer large de Broglie wavelength as well as mean free path. A direct influence of these lengths in the electric transport properties of finite-size samples was neglected in the past. We provide a direct evidence of this effect through the size dependence of the magnetoresistance, which decreases with the sample size even for samples hundreds of micrometers large. Our findings may explain the absence of magnetoresistance in small few graphene layers samples and ask for a general revision of the experimental and theoretical work on the transport properties of this material.