Suchergebnisse

Spin pumping (SP) is a well-established method to generate pure spin currents allowing efficient spin injection into metals and semiconductors avoiding the problem of impedance mismatch. However, to disentangle pure spin currents from parasitic effects due to spin rectification effects (SRE) is a difficult task that is seriously hampering further developments. Here we propose a simple method that allows suppressing SRE contribution to inverse spin Hall effect (ISHE) voltage signal avoiding long and tedious angle-dependent measurements. We show an experimental study in the well-known Py/Pt system by using a coplanar waveguide (CPW). Results obtained demonstrate that the sign and size of the measured transverse voltage signal depends on the width of the sample along the CPW active line. A progressive reduction of this width evidences that SRE contribution to the measured transverse voltage signal becomes negligibly small for sample width below 200 μm. A numerical solution of the Maxwell equations in the CPW-sample setup, by using the Landau-Lifshitz equation with the Gilbert damping term (LLG) as the constitutive equation of the media, and with the proper set of boundary conditions, confirms the obtained experimental results. ; We acknowledge financial support from the Spanish Ministry of Science, Innovation and Universities through Severo Ochoa Program (CEX2019-000917-S), RTI2018-099960-B-I00 and funding from the European Union Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. 645658 (DAFNEOX Project) and FEDER Program. CF thanks Prof. M. Kostylev for fruitful communications. ; With funding from the Spanish government through the 'Severo Ochoa Centre of Excellence' accreditation (CEX2019-000917-S). ; Peer reviewed

Complex oxide thin films grown by using chemical methods are of strong interest because of their low-cost, environment friendly fabrication and easy scalability. However, their introduction in spintronic applications or magnetic devices is still scarce mainly because of concerns regarding their interfacial quality. Here, we report on the preparation by polymer-assisted-deposition (PAD) of epitaxial La0.92MnO3 (LMO) thin films. We demonstrate that ferromagnetic conducting LMO thin films with smooth surfaces (rms ∼ 0.2 nm) can be prepared by PAD. By means of temperature-dependent broadband ferromagnetic resonance (FMR), we show that the LMO film exhibits a four-fold in-plane anisotropy, with [110] being the easy in-plane axis, compatible with strain release from the rhombohedral bulk phase. It has also been found that the isotropic Gilbert damping, α, determined from the broadening of the FMR linewidth, does not show a relevant extrinsic contribution and it exhibits an intraband-like temperature dependence, i.e. it increases as temperature decreases. By capping LMO thin films with a 10 nm thick Pt layer deposited ex situ, damping is substantially enhanced, from a value at 150 K of αLMO ∼ 1 × 10−2 for the bare LMO film to αLMO+Pt ∼ 2.5 × 10−2 for the Pt capped film. This strong increase of magnetic damping is indicative of the transfer of spin momentum from LMO to the Pt layer by spin pumping. Our results demostrate that LMO films grown by PAD may be used as efficient spin source systems in heterostructures for spintronic devices. ; We acknowledge financial support from the Spanish Ministry of Science, Innovation and Universities through Severo Ochoa (SEV-2015-04969), HETEROCS (MAT2015-71664-R), SUMATE (RTI2018-095853-B-C21) and SPINCURIOX (RTI2018-099960-B-I00) projects cofinanced by the European Regional Development Fund. This project has received funding from the European Union through the Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 645658 (DAFNEOX Project) and through the FEDER Program. Hailin Wang acknowledges financial support from the China Scholarship Council (CSC). This work has been performed in the framework of the PhD programme in Materials Science of the Universitat Autònoma de Barcelona, through the China Scholarships Council (CSC)/Universitat Autònoma de Barcelona (UAB) Joint Scholarship. Authors thank Dr B. Bozzo and F. J. Campos for their technical support during magnetic and X-ray diffraction measurements. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI). ; Peer reviewed

The control of the spontaneous formation of nanostructures at the surface of thin films is of strong interest in many different fields, from catalysts to microelectronics, because surface and interfacial properties may be substantially enhanced. Here, we analyze the formation of nickel oxide nanocuboids on top of La2Ni1−xMn1+xO6 double perovskite ferromagnetic thin films, epitaxially grown on SrTiO3 (001) substrates by radio-frequency (RF) magnetron sputtering. We show that, by annealing the films at high temperature under high oxygen partial pressure, the spontaneous segregation of nanocuboids is enhanced. The evolution of the structural and magnetic properties of the films is studied as a function of the annealing treatments at different temperatures. It is shown that the formation of NiOx nanocuboids leads to a nanostructured film surface with regions of locally different electrical transport characteristics. ; We acknowledge financial support from the Spanish Ministry of Science, Innovation and Universities through Severo Ochoa Program (CEX2019-000917-S) and RTI2018-099960-B-I00 (SPINCURIOX) and funding from the European Union's Horizon 2020 research and innovation program under the Marie-Sklodowska-Curie grant agreement No. 645658 (DAFNEOX Project) and FEDER Program. Z.K. acknowledge the support of the Serbian Ministry of Education, Science and Technological Development (III45018). This work has been performed in the framework of the PhD program of the Universitat Autonoma de Barcelona (UAB). ; Peer reviewed

The spontaneous formation of double chemical terminated surfaces of La0.7Sr0.3MnO3 due to deviations from ideal epitaxial growth during its deposition on SrTiO3(001) is presented. The development of surface regions with differentiated topmost composition leads to outstanding surface nanostructuration presenting notably distinct local properties, particularly in terms of electric transport and local work function. Correlation between combined atomic force microscopy and X-ray photoelectron spectroscopy data allows the chemical identification of the two terminations as corresponding to La0.7Sr0.3O and MnO2. The most likely atomistic process at the origin of the surface organization has been interpreted by Monte Carlo simulations that reveal the importance of stacking fault formation as growth proceeds. We present a physical understanding of the experimental results for surfaces in which different electronic responses coexist. The conclusions of the present work can be extended to the growth of other perovskite thin films, therefore broadening the field of functional materials nanostructuration. ; This work has been supported by the Spanish Government under projects MAT2013-47869-C4 and MAT2015-71664-R. The ICMAB members acknowledge the Spanish MINECO through the project MAT2015-68994-REDC and the Severo Ochoa Program (SEV-2015-0496), FEDER program and the Generalitat de Catalunya through 2014 SGR 501. L.L.M. thanks the Spanish MINECO for a FPI BES-2013-063424 fellowship. J.J.M. thanks the Centro de Computacioń Cientıfí ca (CCC) of the Universidad Autónoma de Madrid for computing time. ; Peer reviewed

Spin to charge conversion process in a broad range of temperatures is studied in La0.92MnO3/Pt bilayers prepared by polymer-assisted deposition (PAD). It is shown that an excellent LMO/Pt interface can be obtained in spite of using ex situ deposition of the Pt layer. The values obtained for the effective spin-mixing conductance, g↑↓eff = 0.76 × 1015 cm−2, suggest that significant spin transport across the LMO/Pt interface could be achieved. Spin pumping experiments generate a transversal voltage signal VISHE, due to spin to charge conversion via inverse spin Hall effect, that has been detected down to about 100 K with values of the spin-Hall angle, θSH, of about 2.5%, slightly decreasing on reducing temperature in the analyzed temperature range. These results indicate that LMO is a promising perovskite building block for all-oxide multifunctional high-frequency spintronics devices and that PAD technique provides oxide epitaxial thin films of good quality adequate for spintronic applications. ; We acknowledge financial support from the Spanish Ministry of Science, Innovation and Universities through Severo Ochoa (CEX2019-000917-S), and SPINCURIOX (RTI2018-099960-BI00) and AMONANO (PID2020-112914RB-I00) projects co-financed by the European Regional Development Funds. AMONANO also received funding from the European Union's Horizon 2020 research and innovation program under grant agreement no. 823717-ESTEEM3. Hailin Wang acknowledges financial support from the China Scholarship Council (CSC). ; With funding from the Spanish government through the 'Severo Ochoa Centre of Excellence' accreditation (CEX2019-000917-S). ; Peer reviewed

Interfacial dissimilarity has emerged in recent years as the cornerstone of emergent interfacial phenomena, while enabling the control of electrical transport and magnetic behavior of complex oxide epitaxial films. As a step further toward the lateral miniaturization of functional nanostructures, this work uncovers the role of misfit dislocations in creating periodic surface strain patterns that can be efficiently used to control the spatial modulation of mass transport phenomena and bandwidth-dependent properties on a ≈20 nm length scale. The spontaneous formation of surface strain-relief patterns in La0.7Sr0.3MnO3/LaAlO3 films results in lateral periodic modulations of the surface chemical potential and tetragonal distortion, controlling the spatial distribution of preferential nucleation sites and the bandwidth of the epilayer, respectively. These results provide insights into the spontaneous formation of strain-driven ordered surface patterns, topographic and functional, during the growth of complex oxide heterostructures on lengths scales far below the limits achievable through top-down approaches. ; The authors thank Dr. Belén Ballesteros for her assistance with electron microscopy experiments. This research was sponsored by the Spanish MINECO ("Severo Ochoa" Programme for Centres of Excellence in R&D: SEV- 2015-0496, MAT2015-71664-R, FEDER program, MAT2012-33207, and MAT2013-47869-C4-1-P), and the European Union Horizon 2020 research and innovation program under the Marie Sklodowska–Curie grant agreement No. 645658. The authors also acknowledge fi nancial aid from the Generalitat de Catalunya (2014 SGR 501). N.B. and F.S. also acknowledge funding from the European Union Seventh Framework Programme under Grant Agreement 312483-ESTEEM2 (Integrated Infrastructure Initiative I3) for providing access to aberration corrected electron microscope at CEMES (Toulouse). N.B. thanks the Spanish MINECO for fi nancial support through the FPI program. F.S. acknowledges support from the Labex (Excellence Laboratory) NEXT for a visiting scientist fellowship at CEMES (Toulouse, France). Z.K. is grateful for the support from the Ministry of Education, Science, and Technological Development of the Republic of Serbia through Project III45018. ; Peer reviewed

The fabrication procedure of hollow iron oxide nanoparticles with a large surface to volume ratio by a single-step gas condensation process at ambient temperature is presented. Fe clusters formed during the sputtering process are progressively transformed into hollow cuboids with oxide shells by the Kirkendall mechanism at the expense of oxygen captured inside the deposition chamber. TEM and Raman spectroscopy techniques point to magnetite as the main component of the nanocuboids; however, the magnetic behavior exhibited by the samples suggests the presence of FeO as well. In addition, these particles showed strong stability after several months of exposure to ambient conditions, making them of potential interest in diverse technological applications. In particular, these hierarchical hollow particles turned out to be very efficient for both As(III) and As(V) absorption (326 and 190 mg/g, respectively), thus making them of strong interest for drinking water remediation. ; We kindly acknowledge the assistance of Guillaume Sauthier, from ICN2, for helping us with valuable X-ray photoelectron investigations. Financial support from the Spanish Ministry of Economy and Competitiveness, through the "Severo Ochoa" Program for Centres of Excellence in R&D (SEV- 2015-0496), MAT2015-71664-R, FEDER, and funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 645658 (DAFNEOX Project) is acknowledged. N.B. thanks the Spanish MINECO for financial support through the FPI program. ; Peer reviewed

In this work we report on the epitaxial growth of La2NiMnO6 double perovskite thin films on top of (001) oriented SrTiO3 substrates by RF magnetron sputtering. The influence of oxygen pressure (PO2 ) and growth temperature on the microstructure, stoichiometry of the films, and magnetic and transport properties is thoroughly investigated. It is found that high oxygen pressure promotes the growth of stoichiometric films, with a Ni/Mn ratio almost equal to 1. However, these films exhibit poor ferromagnetic properties with respect to the expected optimum values corresponding to ferromagnetic ordering mediated by superexchange interaction between Mn4+ and Ni2+ according to the Goodenough-Kanamori rules. Most interestingly, films grown at low PO2 exhibit Ni/Mn ratios below 1, but ferromagnetic properties close to the optimal ones. The valence balance between Ni and Mn ions in nonstoichiometric sample has been elucidated by X-ray absorption spectroscopy. The results indicate that Ni deficiency plays a crucial role in the puzzling insulating ferromagnetic behavior observed in nonstoichiometric samples. ; M.B.-S., Ll.B., F.S., B.B., C.F., B.M., and A.P. acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through the "Severo Ochoa" Programme for Centres of Excellence in R&D (SEV-2015-0496), and Project MAT2015-71664-R. This work has received funding from the European Union's Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Grant Agreement No. 645658 (DAFNEOX Project). Z.K. acknowledge the support of the Serbian Ministry of Education, Science and Technological Development (III45018). Authors thank ALBA synchrotron (Spain) for the provision of beamtime. ; Peer reviewed