Thin films of BiFeO₃, VO₂, and BiFeO₃/VO₂ were grown on SrTiO₃(100) and Al₂O₃(0001) monocrystalline substrates using radio frequency and direct current sputtering techniques. To observe the effect of the coupling between these materials, the surface of the films was characterized by profilometry, atomic force microscopy, and X-ray photoelectron spectroscopy. The heterostructures, monolayers, and bilayers based on BiFeO₃ and VO₂ grew with good adhesion and without delamination or signs of incompatibility between the layers. A good granular arrangement and RMS roughness between 1 and 5 nm for the individual layers (VO₂ and BiFeO₃) and between 6 and 18 nm for the bilayers (BiFeO₃/VO₂) were observed. Their grain size is between 20 nm and 26 nm for the individual layers and between 63 nm and 67 nm for the bilayers. X-ray photoelectron spectroscopy measurements show a higher proportion of V⁴⁺, Bi³⁺, and Fe³⁺ in the films obtained. The homogeneous ordering, low roughness, and oxidation states on the obtained surface show a good coupling in these films. The I-V curves show ohmic behavior at room temperature and change with increasing temperature. The effect of coupling these materials in a thin film shows the appearance of hysteresis cycles, I-V and R-T, which is typical of materials with high potential in applications, such as resistive memories and solar cells.

This paper presents a novel hybrid modulation algorithm which improves the harmonic performance of eight of the most common pulse width modulation (PWM) algorithms for voltage source inverters (VSI) in the electric drive field. From harmonic analysis of these eight algorithms, a methodology was established for designing a hybrid modulation scheme offering superior harmonic performance. The algorithm so designed was validated theoretically by calculating the total harmonic distortion factor F_DIST and experimentally by measuring the weighted total harmonic distortion factor V_WTHD. Este artículo presenta el diseño y validación de un nuevo algoritmo de modulación por ancho de pulso (PWM) híbrido que supe-ra el desempeño armónico de varios algoritmos de modulación empleados en procesos de conversión de potencia en acciona-mientos eléctricos AC. A partir del análisis armónico de los algoritmos PWM más comunes en la literatura, se establece una me-todología para diseñar un esquema de modulación híbrido que ofrece un desempeño armónico superior; este desempeño es verificado teórica y experimentalmente utilizando el factor de distorsión armónica taEste artículo presenta el diseño y validación de un nuevo algoritmo de modulación por ancho de pulso (PWM) híbrido que supera el desempeño armónico de varios algoritmos de modulación empleados en procesos de conversión de potencia en accionamientos eléctricos AC. A partir del análisis armónico de los algoritmos PWM más comunes en la literatura, se establece una metodología para diseñar un esquema de modulación híbrido que ofrece un desempeño armónico superior; este desempeño es verificado teórica y experimentalmente utilizando el factor de distorsión armónica total F_DIST y el índice de distorsión armónica de corriente V_WTHD.otal FDIST y el índice de distorsión armónica de corriente VWTHD.

Thin films of BiFeO3 (BFO), VO2 and BFO/VO2 were grown on SrTiO3(100) and Al2O3(0001) monocrystalline substrates using the RF and DC sputtering techniques. The surface of the films was characterized by profilometry, AFM, and XPS. The heterostructures have roughnesses between 0.2 and 16 nm and a grain size between 20 nm and 67 nm. XPS measurements show a higher proportion of the V4+ and Bi3+ oxides. In the Fe region, a higher proportion of Fe3+ is shown in the films. The homogeneous ordering, low roughnesses, and the oxidation states on the obtained surface show a good coupling in these films. The I-V curves show ohmic behavior at room temperature and change with increasing temperature. The effect of coupling these materials in a thin film shows the appearance of hysteresis cycles I-V and R-T, typical of materials with high potential in applications such as resistive memories and solar cells.

Half-metals are compounds with a 100% spin polarization in one direction: they are metallic for one spin direction but insulators, or semiconductors, for the other direction. From the viewpoint of the density of states (DOS) it is finite at the Fermi level for one spin direction and negligible small for the other. In this work the current vs. voltage characteristics I-V, for a Superconductor- Insulator-Half metal have been calculated with a simple and straightforward procedure which essentially involves a product of the corresponding DOS for the electrodes of the junction. Nb, a BCS superconductor, and CrO₂, a well-known half-metal, have been considered as electrodes which are separated by a perfect insulator to form the SC-I-HM tunnel junction. Our results show that the I-V characteristics for a SC-I-HM junction are useful for obtaining the majority spin part of the DOS and the gap for the minority spin part or as an experimental confirmation of theoretical calculation of DOS for a half-metal; furthermore, such junctions may be used as a spin valve for certain polarization voltages or as a component of a more sophisticated spintronic device.