RESUMO
It is shown in this work that a synchronous measurement setup is able to conveniently and accurately retrieve ferromagnetic resonance's (FMR) main physical properties from a permalloy sample. The apparatus used comprises a vector network analyzer (VNA), coupled with external DC coils, driven by a controllable power supply. A permalloy thin film sample was subjected to a microwave signal through a grounded coplanar waveguide. A square wave signal generated by an Arduino microcontroller drives the coils to a triangular, 65.4 ms period magnetic field. This field's half-cycle is synchronized to match a zero-span sampling time at the VNA. The system has the advantage of fast results, as the typical FMR lorentzian curve is completed in a few seconds and shown immediately on the VNA's scattering parameter S21 trace graph. The system showed an improved signal-to-noise ratio of 51.7 at 10 GHz over 24.3 for the 100 nm thick permalloy- sample used in this work. A magnetic field resonance point, collected at 10 GHz, showed a five-fold improvement in the standard-error.
RESUMO
Several experimental works currently demonstrate that metallic nano-oxides and carbon nanomaterials expected to be diamagnets, in fact, behave as ferromagnets at room temperature. More than scientifically intriguing, this unconventional and unexpected ferromagnetism pave the way for innovation products and novel nanotechnological applications, gathering the magnetism to interesting functionalities of these nanomaterials. Here, we investigate the non-conventional ferromagnetism observed at high temperatures in nanocrystalline cerium dioxide (CeO2or nanoceria) thin films that are optically transparent to visible light. Nanoceria exhibits several concrete applications in catalytic processes, photovoltaic cells, solid-state fuel cells, among others, which are mostly due to natural presence of oxygen vacancies and easy migration of the oxygen through the structure. The ferromagnetism in non-stoichiometric nanocrystaline ceria can be consistently described by ab initio electronic structure calculations, which support that oxygen vacancies cause the formation of magnetic moments and can provide a robust interconnectivity within magnetic polarons theoretical framework. Additionally, we present a conceptual model to account the oxygen transport to the non-conventional ferromagnetism at temperatures well above room temperature. The approach is complementary to the thermally-activated effective transfers of charge and spin around oxygen vacancy centers.
RESUMO
In this paper, we have developed an analytic method for describing Airy-type beams truncated by finite apertures. This new approach is based on suitable superposition of exponentially decaying Airy beams. Regarding both theoretical and numerical aspects, the results here shown are interesting because they have been quickly evaluated through a simple analytic solution, whose propagation characteristics agree with those already published in literature through the use of numerical methods. To demonstrate the method's potentiality three different truncated beams have been analyzed: ideal Airy, Airy-Gauss and Airy-Exponential.