Direct visualization of Rashba-split bands and spin/orbital-charge interconversion at KTaO₃ interfaces

Rashba interfaces have emerged as promising platforms for spin-charge interconversion through the direct and inverse Edelstein effects. Notably, oxide-based two-dimensional electron gases display a large and gate-tunable conversion efficiency, as determined by transport measurements. However, a direct visualization of the Rashba-split bands in oxide two-dimensional electron gases is lacking, which hampers an advanced understanding of their rich spin-orbit physics. Here, we investigate KTaO3 two-dimensional electron gases and evidence their Rashba-split bands using angle resolved photoemission spectroscopy. Fitting the bands with a tight-binding Hamiltonian, we extract the effective Rashba coefficient and bring insight into the complex multiorbital nature of the band structure. Our calculations reveal unconventional spin and orbital textures, showing compensation effects from quasi-degenerate band pairs which strongly depend on in-plane anisotropy. We compute the band-resolved spin and orbital Edelstein effects, and predict interconversion efficiencies exceeding those of other oxide two-dimensional electron gases. Finally, we suggest design rules for Rashba systems to optimize spin-charge interconversion performance

FeCo Nanowire-Strontium Ferrite Powder Composites for Permanent Magnets with High-Energy Products

Due to the issues associated with rare-earth elements, there arises a strong need for magnets with properties between those of ferrites and rare-earth magnets that could substitute the latter in selected applications. Here, we produce a high remanent magnetization composite bonded magnet by mixing FeCo nanowire powders with hexaferrite particles. In the first step, metallic nanowires with diameters between 30 and 100 nm and length of at least 2 {\mu}m are fabricated by electrodeposition. The oriented as-synthesized nanowires show remanence ratios above 0.76 and coercivities above 199 kA/m and resist core oxidation up to 300 {\deg}C due to the existence of a > 8 nm thin oxide passivating shell. In the second step, a composite powder is fabricated by mixing the nanowires with hexaferrite particles. After the optimal nanowire diameter and composite composition are selected, a bonded magnet is produced. The resulting magnet presents a 20% increase in remanence and an enhancement of the energy product of 48% with respect to a pure hexaferrite (strontium ferrite) magnet. These results put nanowire-ferrite composites at the forefront as candidate materials for alternative magnets for substitution of rare earths in applications that operate with moderate magnet performance

Improvement of the magnetic properties of SrFe12O19 ceramics by tailored sintering with SiO2 addition

[EN] In order to obtain competitive strontium ferrite sintered magnets, SiO2 and CaO are added to avoid exaggerated grain growth. Besides favoring proper densification, these additives prevent the collapse of coercivity associated to grain growth. However, these additives may lead to slight decreases in density and the formation of paramagnetic α-Fe2O3 that hampers magnetization. Here, with the motivation of simplifying the production process, we present a study to maximize the magnetic performance of strontium ferrite ceramics using silica as the sole additive. A microscopic study offers insights into the grain growth mechanism activated by Silica. As a result, a compromise between relative density, coercivity and saturation magnetization is attained. It is found that sintering for 4 h up to 1200 °C with a SiO2 content of 1 wt% leads to the best compromise between coercivity, magnetization and density values. Competitive densities are reported in the absence of CaO, the usual co-additive. In addition, Confocal Raman Microscopy is employed for the first time to characterize the decomposition of strontium ferrite onto α-Fe2O3-Fe2O3.This work is supported by the Spanish Ministerio de Ciencia, Innovación y Universidades through Project no. MAT2017-86450-C4-1-R, RTI2018-095303-A-C52 and through the Ramón y Cajal Contract RYC-2017-23320 and Juan de la Cierva Program FJC2018-035532-I; and by the European Commission through the H2020 Project no. 720853 (AMPHIBIAN)

FeCo nanowire−strontium ferrite powder composites for permanent magnets with high-energy products

Due to the issues associated with rare-earth elements, there arises a strong need for magnets with properties between those of ferrites and rare-earth magnets that could substitute the latter in selected applications. Here, we produce a high remanent magnetization composite bonded magnet by mixing FeCo nanowire powders with hexaferrite particles. In the first step, metallic nanowires with diameters between 30 and 100 nm and length of at least 2 μm are fabricated by electrodeposition. The oriented as-synthesized nanowires show remanence ratios above 0.76 and coercivities above 199 kA/m and resist core oxidation up to 300 °C due to the existence of a >8 nm thin oxide passivating shell. In the second step, a composite powder is fabricated by mixing the nanowires with hexaferrite particles. After the optimal nanowire diameter and composite composition are selected, a bonded magnet is produced. The resulting magnet presents a 20% increase in remanence and an enhancement of the energy product of 48% with respect to a pure hexaferrite (strontium ferrite) magnet. These results put nanowire−ferrite composites at the forefront as candidate materials for alternative magnets for substitution of rare earths in applications that operate with moderate magnet performance.We would like to thank Dr. Vić tor Fuertes for his advice on the processing of the bonded magnets. This work is supported by the Spanish Ministerio de Economía y Competitividad y Ministerio de Ciencia e Innovación (Project Nos. MAT2017- 86450-C4-1-R, MAT2015-64110-C2-1-P, MAT2015-64110- C2-2-P, MAT2017-87072-C4-2-P, RTI2018-095303-A-C52, and FIS2017-82415-R) and by the European Commission through Project H2020 (No. 720853; AMPHIBIAN). C.G.-M. acknowledges financial support from MICINN through the “Juan de la Cierva” Program (FJC2018-035532-I). A.Q. acknowledges financial support from MICINN through the “Ramón y Cajal” Program (RYC-2017-23320). The work also is funded by the Regional Government of Madrid (Project S2018/ NMT-4321; NANOMAGCOST)