RESUMO
Spin injection and extraction are at the core of semiconductor spintronics. Electrical injection is one method of choice for the creation of a sizeable spin polarization in a semiconductor, requiring especially tailored tunnel or Schottky barriers. Alternatively, optical orientation can be used to generate spins in semiconductors with significant spin-orbit interaction, if optical selection rules are obeyed, typically by using circularly polarized light at a well-defined wavelength. Here we introduce a novel concept for spin injection/extraction that combines the principle of a solar cell with the creation of spin accumulation. We demonstrate that efficient optical spin injection can be achieved with unpolarized light by illuminating a p-n junction where the p-type region consists of a ferromagnet. The discovered mechanism opens the window for the optical generation of a sizeable spin accumulation also in semiconductors without direct band gap such as Si or Ge.
RESUMO
For the development of future magnetic data storage technologies, the ultrafast generation of local magnetic fields is essential. Subnanosecond excitation of the magnetic state has so far been achieved by launching current pulses into micro-coils and micro-striplines and by using high-energy electron beams. Local injection of a spin-polarized current through an all-metal junction has been proposed as an efficient method of switching magnetic elements, and experiments seem to confirm this. Spin injection has also been observed in hybrid ferromagnetic-semiconductor structures. Here we introduce a different scheme for the ultrafast generation of local magnetic fields in such a hybrid structure. The basis of our approach is to optically pump a Schottky diode with a focused, approximately 150-fs laser pulse. The laser pulse generates a current across the semiconductor-metal junction, which in turn gives rise to an in-plane magnetic field. This scheme combines the localization of current injection techniques with the speed of current generation at a Schottky barrier. Specific advantages include the ability to rapidly create local fields along any in-plane direction anywhere on the sample, the ability to scan the field over many magnetic elements and the ability to tune the magnitude of the field with the diode bias voltage.
RESUMO
Combining X-ray magnetic circular dichroism (X-MCD) with a transmission X-ray microscope (TXM) allows to image element-specifically magnetic domain structures with 25nm lateral resolution. Both in-plane and out-of-plane systems can be studied in applied magnetic fields. Thus field-dependent parameters, as individual nucleation fields in magnetic nanostructures can be deduced and related to morphology. Images of thermomagnetically written bits in magneto-optical TbFeCo media proof the reliability of the writing process and the importance of an exact thermal design of the systems. Domains observed at corresponding Co L edges proof the chemical sensitivity of M-TXM and its potential to image few monolayer systems.
RESUMO
The aim of the study was to investigate the influence of dental alloys and their components on magnetic resonance imaging of the temporomandibular joint. A plaster and a water- filled acrylic resin phantom - representing the disc and the condyle of the TMJ - were used. Cylindrical crow-type samples of 13 alloys and 14 pure substances were investigated. All alloys were examined with regard to their magnetic susceptibility, using a vibrating sample magnetometer. Metallic artefacts appeared on spin-echo technique as distortions, and on gradient-echo technique signal loss could be observed. Precious alloys were shown to be diamagnetic. The non precious alloys we investigated were paramagnetic. Paramagnetic alloys with a magnetic molar-susceptibility Cmol > 2000 x10(-6) cm3/mol can produce clinically relevant artefacts.
