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7 páginas, 9 figuras.-- PACS number(s): 75.60.Jk, 75.30.Kz, 82.33.Vx.-- et al. ; We report experiments on magnetic avalanches in the intermetallic compound Gd5Ge4. Kinetics of the avalanches have been studied and compared with the theory of magnetic deflagration. We show that the data fit well into the theoretical framework of deflagration. This adds Gd5Ge4 to the growing family of materials (that now includes molecular magnets and manganites) which exhibit this phenomenon. The "burning" of the metastable magnetic phase involves a magnetostructural transition alongside the reordering of spins. ; J.M.H. thank Spanish Ministry of Education and Science for the research grant. J.M.H. thanks University of Barcelona for the Ramon y Cajal research contract. J.T. thanks Catalan Institute of Research and Advanced Studies for the financial support. P.A. acknowledges financial support by the Aragon Regional Government (through Project No. E26). E.M.C. acknowledges support from the University of Barcelona and from the U.S. National Science Foundation through Grant No. DMR-0703639. ; Peer reviewed

This article belongs to the Special Issue Nanomaterials for the Advanced Manufacturing of Electronic Devices. ; The growth of ferromagnetic nanostructures by means of focused-Ga+-beam-induced deposition (Ga+-FIBID) using the Co2(CO)8 precursor has been systematically investigated. The work aimed to obtain growth conditions allowing for the simultaneous occurrence of high growth speed, good lateral resolution, low electrical resistivity, and ferromagnetic behavior. As a first result, it has been found that the competition between deposition and milling that is produced by the Ga+ beam is a limiting factor. In our working conditions, with the maximum available precursor flux, the maximum deposit thickness has been found to be 65 nm. The obtained volumetric growth rate is at least 50 times higher than in the case of deposition by focused-electron-beam-induced deposition. The lateral resolution of the deposits can be as good as 50 nm while using Ga+-beam currents lower than 10 pA. The high metallic content of the as-grown deposits gives rise to a low electrical resistivity, within the range 20-40 µΩ·cm. Magnetic measurements confirm the ferromagnetic nature of the deposits at room temperature. In conclusion, the set of obtained results indicates that the growth of functional ferromagnetic nanostructures by Ga+-FIBID while using the Co2(CO)8 precursor is a viable and competitive technique when compared to related nanofabrication techniques. ; This research was funded by the Spanish Ministry of Science, grant numbers MAT2017-82970-C2 and MAT2018-102627-T, and by the Aragon regional government, grant number E13_17R, with support from the European Social Fund (Construyendo Europa desde Aragón). ; Peer reviewed

The spinel CoCr2O4 (CCO) is one of the few bulk multiferroics with net magnetic moment. However, studies on the properties of CCO thin films are scarce. Here, we investigate the interplay between microstructure and magnetism of a series of CCO epitaxial thin films by means of x-ray diffraction, magnetometry, and aberration-corrected scanning transmission electron microscopy (STEM). Optimum pristine CCO films can be grown on a substrate with spinel structure (MgAl2O4), despite the large lattice mismatch of ∼3%. On the contrary, a substrate with lower lattice mismatch (∼1%) but with the rock salt structure (MgO) favors the degradation of the CCO crystal quality by forming antiphase boundaries (APBs), drastically weakening the magnetization, in agreement with reports for other spinel films. Nevertheless, our results also show that the type and number of APBs can be tuned by changing the growth temperature to favor the ferromagnetic alignment between antiphase domains, giving rise to a partial recovery of the magnetization. ; Financial support is acknowledged from the European Union under the Seventh Framework Programme under a contract for an Integrated Infrastructure Initiative Reference No. 312483-ESTEEM2, the Spanish Ministerio de Economía y Competitividad through Project No.MAT2014-51982-C2 and through the "Severo Ochoa" award Programme for Centres of Excellence in R&D (Project No. SEV-2015-0496), the Zernike Institute for Advanced Materials, The Netherlands, regional Gobierno de Aragón through Project No. E26, including Fondo Europeo de Desarrollo Regional (FEDER) funding. ; Peer reviewed

Under the terms of the Creative Commons Attribution 3.0 Unported License to their work. ; The morphology and the quantitative composition of the Fe-Si interface layer forming at each Fe layer of a (Fe/Si)3 multilayer have been determined by means of conversion electron Mössbauer spectroscopy (CEMS) and high-resolution transmission electron microscopy (HRTEM). For the CEMS measurements, each layer was selected by depositing the Mössbauer active 57Fe isotope with 95% enrichment. Samples with Fe layers of nominal thickness dFe = 2.6 nm and Si spacers of dSi = 1.5 nm were prepared by thermal evaporation onto a GaAs(001) substrate with an intermediate Ag(001) buffer layer. HRTEM images showed that Si layers grow amorphous and the epitaxial growth of the Fe is good only for the first deposited layer. The CEMS spectra show that at all Fe/Si and Si/Fe interfaces a paramagnetic c-Fe1− x Si phase is formed, which contains 16% of the nominal Fe deposited in the Fe layer. The bottom Fe layer, which is in contact with the Ag buffer, also contains α-Fe and an Fe1− x Si x alloy that cannot be attributed to a single phase. In contrast, the other two layers only comprise an Fe1− x Si x alloy with a Si concentration of ≃0.15, but no α-Fe. ; The financial support of the Spanish MINECO MAT2011- 23791, the Aragonese DGA-IMANA E34 (co-funded by Fondo Social Europeo) and that received from the European Union FEDER funds is acknowledged. L.B.-R. acknowledges the Spanish MINECO FPU 2010 grant. ; Peer Reviewed

Bulk SrTiO3 is a quantum paraelectric in which an antiferrodistortive distortion below ≈105 K and quantum fluctuations at low temperature preclude the stabilization of a long-range ferroelectric state. However, biaxial mechanical stress, impurity doping, and Sr nonstoichiometry, among other mechanisms, are able to stabilize a ferroelectric or relaxor ferroelectric state at room temperature, which develops into a longer-range ferroelectric state below 250 K. In this paper, we show that epitaxial SrTiO3 thin films grown under tensile strain on DyScO3 exhibit a large reduction of thermal conductivity, of ≈60% at room temperature, with respect to identical strain-free or compressed films. The thermal conductivity shows a further reduction below 250 K, a temperature concurrent with the peak in the dielectric constant [J. H. Haeni et al., Nature (London) 430, 758 (2004)]. These results suggest that strain gradients in the relaxor and ferroelectric phase of SrTiO3 are very effective phonon scatterers, limiting the thermal transport in this material. ; F.R. acknowledges financial support of the Ministerio de Economía y Competitividad of Spain (Project No. MAT2016- 80762-R), and Xunta de Galicia (Centro Singular de Investigación de Galicia accreditation 2016-2019) and the European Union (European Regional Development Fund ERDF), and the European Commission through the project 734187 - SPICOLOST (H2020-MSCA-RISE-2016). J.A.M. would like to acknowledge the National Science Foundation, Division of Electrical, Communication and Cyber Systems, Award No. 1901972. This work was supported by the National Natural Science Foundation of China (Grant No. 51876186), Natural Science Foundation of Zhejiang Province (Grant No. LZ19E060002), the Fundamental Research Funds for the Central Universities (K20200145), and ZJUI with W.-L. Ong as one of the Principal Supervisors. ; Peer reviewed

In this work, we present a detailed investigation of the magnetic properties of cobalt nanospheres grown on cantilever tips by focused electron beam induced deposition (FEBID). The cantilevers are extremely soft and the cobalt nanospheres are optimized for magnetic resonance force microscopy (MRFM) experiments, which implies that the cobalt nanospheres must be as small as possible while bearing high saturation magnetization. It was found that the cobalt content and the corresponding saturation magnetization of the nanospheres decrease for nanosphere diameters less than 300 nm. Electron holography measurements show the formation of a magnetic vortex state in remanence, which nicely agrees with magnetic hysteresis loops performed by local magnetometry showing negligible remanent magnetization. As investigated by local magnetometry, optimal behavior for high-resolution MRFM has been found for cobalt nanospheres with a diameter of ≈200 nm, which present atomic cobalt content of ≈83 atom % and saturation magnetization of 106 A/m, around 70% of the bulk value. These results represent the first comprehensive investigation of the magnetic properties of cobalt nanospheres grown by FEBID for application in MRFM. ; This work was supported by Spanish Ministry of Economy and Competitivity through projects No. MAT2014-51982-C2-1-R, MAT2014-51982-C2-2-R and MAT2015-69725-REDT (including FEDER funds), by the Aragon Regional Government, and by EU (Cost Action CM1301- CELINA and ESTEEM2 projects). ; Peer reviewed

Defects play an important role in tailoring the optoelectronic properties of materials. Here we demonstrate that sulphur vacancies are able to engineer sub-band photoresponse into the short-wave infrared range due to formation of in-gap states in Bi2S3 single crystals supported by density functional (DF) calculations. Sulfurization and subsequent refill of the vacancies results in faster response but limits the spectral range to the near infrared as determined by the bandgap of Bi2S3. A facile chemical treatment is then explored to accelerate the speed of sulphur deficient (SD)-based detectors on the order of 10 ms without sacrificing its spectral coverage into the infrared, while holding a high D* close to 10^15 Jones in the visible-near infrared range and 10^12 Jones at 1.6 um. This work also provides new insights into the role sulphur vacancies play on the electronic structure and, as a result, into sub-bandgap photoresponse enabling ultrasensitive, fast and broadband photodetectors. ; The authors acknowledge financial support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 725165), the Spanish Ministry of Economy and Competitiveness (MINECO), and the "Fondo Europeo de Desarrollo Regional" (FEDER) through grant TEC2017-88655-R. The authors also acknowledge financial support from Fundacio Privada Cellex, the program CERCA and from the Spanish Ministry of Economy and Competitiveness, through the "Severo Ochoa" Programme for Centres of Excellence in R&D (SEV-2015-0522). Y.Y. acknowledges support from the National Natural Science Foundation of China under grant no. 61805045. S.C. acknowledges support from Marie Curie Standard European Fellowship ("NAROBAND", H2020-MSCA-IF-2016-750600). Furthermore, the research leading to these results has received funding from the European Union H2020 Programme under grant agreement no. 785219 Graphene Flagship ; Peer reviewed

Chemical doping and epitaxy can be used to tailor the magnetoelectric properties of multiferroic thin films, such as SrMnO3. Here, we study the dependence of the magnetic order temperatures of Sr1−xBaxMnO3 thin films on epitaxial strain and Ba content. Combining low-energy muon spin spectroscopy and scanning transmission electron microscopy, the broadness of the magnetic transition is attributed to the presence of a Mn-O-Mn angle gradient along the out-of-plane direction. We also demonstrate that the unit cell volume is the key parameter to determine the Néel temperature in Sr1−xBaxMnO3 thin films showing G-type antiferromagnetic order. The occurrence of a simultaneously ferroelectric and ferromagnetic ground state at high strain levels is suggested for the Sr0.8Ba0.2MnO3 thin film deposited on TbScO3. ; This work has been supported by the Spanish Ministry of Science through Project Nos. MAT2017-82970-C2-1-R and MAT2017-82970-C2-2-R and by the Aragon Regional Government through Project Nos. E13_17R and E28_17R (Construyendo Europa desde Aragón). ; Peer reviewed

Double-walled oxide nanotube structures are interesting for a wide range of applications, from photocatalysis to drug delivery. In this work, a progressive oxidation method to fabricate double-walled nanotube structures is reported in detail. The approach is based on the electrodeposition of metallic iron nanowires, in porous alumina templates, followed by a selective chemical etching, nanoscale Kirkendall effect, a fast oxidation and out-diffusion of the metallic core structure during thermal annealing. To validate the formation mechanism of such core-shell structure, chemical composition and atomic structure were assessed. The resulting hematite nanotubes have a high degree of uniformity, along several microns, and a nanoscopic double-walled structure. ; J. Azevedo would like to acknowledge the Portuguese Foundation for Science and Technology (FCT) for funding (CEECIND/03937/2017). C.T. Sousa thanks FCT for financial support through the Investigador FCT program (Contract No. IF/01159/2015). M.P. Fernández-García acknowledges financial support through Spanish MINECO (research project RTI2018-094683-B-C52); Gobierno del Principado de Asturias and FICyT (through research project FC-GRUPIN-IDI/2018/000185) and University of Oviedo for R&D project 2018/00061/008 in the competitive call PAPI-18-EMERG-8. The authors are thankful to Elettra Sincrotrone for allocating beam-time and their experimental facilities. This work was partially supported by the Project POCI-01-0145-FEDER-006939 (Laboratory for Process Engineering, Environment, Biotechnology and Energy – LEPABE and "SunStorage - Harvesting and storage of solar energy", with reference POCI-01-0145-FEDER-016387, funded by European Regional Development Fund (ERDF), through COMPETE 2020 - Operational Programme for Competitiveness and Internationalization (OPCI), by FCT - Portuguese Foundation for Science and Technology I.P. This work was financially supported by: Project PTDC/EQU-EQU/30510/2017 - POCI-01-0145-FEDER-030510 – Sunflow "Solar energy storage into redox flow batteries" funded by FEDER funds through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI) and by national funds (PIDDAC) through FCT/MCTES. This work was also supported by the Portuguese Fundação para a Ciência e Tecnologia (FCT) and COMPETE 2020 (FEDER) under the projects POCI-01-0141-FEDER-032527, PTDC/FIS-MAC/31302/2017, MIT-EXPL/IRA/0012/2017, PTDC/CTM-CTM/28676/2017 and PTDC/FIS-OTI/32257/2017 and the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement No. 734801. ; Peer reviewed

Half-metallic ferromagnetic La0.7Sr0.3MnO3 (LSMO) represents an appealing candidate to be integrated on silicon substrates for technological devices such as sensors, data storage media, IR detectors, and so on. Here, we report high-quality epitaxial LSMO thin films obtained by an original combination of chemical solution deposition (CSD) and molecular beam epitaxy (MBE). A detailed study of the thermal, chemical, and physical compatibility between SrTiO3 (STO)/Si buffer layers and LSMO films, grown by MBE and CSD, respectively, enables a perfect integration of both materials. Importantly, we show a precise control of the coercive field of LSMO films by tuning the mosaicity of the STO/Si buffer layer. These results demonstrate the enormous potential of combining physical and chemical processes for the development of low-cost functional oxide-based devices compatible with the complementary metal oxide semiconductor technology. ; ACG acknowledges the financial support from the French Agence Nationale pour la Recherche (ANR), project Q-NOSS ANR-16-CE09-0006-01 and École Centrale de Lyon under the BQR 2016 project. The research leading to these results has received funding from the European Union Seventh Framework Program under Grant Agreement 312483 - ESTEEM2 (Integrated Infrastructure Initiative–I3). This project has received funding from the EU‐H2020 research and innovation Program under grant agreement No 654360 having benefitted from the access provided by ICMAB-CSIC in Barcelona within the framework of the NFFA‐Europe Transnational Access Activity. Fruitful discussions with Pr. F. Rivadulla from USC are highly acknowledged. INL authors acknowledge the European Commission for funding the project TIPS (H2020-ICT-02-2014-1-644453). We thank P. Regreny, C. Botella, and J. B. Goure for the MBE technical assistance on the Nanolyon technological platform. ; Peer reviewed

Iron nanostructures grown by focused electron beam induced deposition (FEBID) are promising for applications in magnetic sensing, storage and logic. Such applications require a precise design and determination of the coercive field (H C), which depends on the shape of the nanostructure. In the present work, we have used the Fe2(CO)9 precursor to grow iron nanowires by FEBID in the thickness range from 10 to 45 nm and width range from 50 to 500 nm. These nanowires exhibit an Fe content between 80 and 85%, thus giving a high ferromagnetic signal. Magneto-optical Kerr characterization indicates that H C decreases for increasing thickness and width, providing a route to control the magnetization reversal field through the modification of the nanowire dimensions. Transmission electron microscopy experiments indicate that these wires have a bell-type shape with a surface oxide layer of about 5 nm. Such features are decisive in the actual value of H C as micromagnetic simulations demonstrate. These results will help to make appropriate designs of magnetic nanowires grown by FEBID. ; This work was supported by Spanish Ministry of Economy and Competitivity through project No. MAT2011-27553-C02, MAT2011-28532-C03-02 and MAT2014-51982-C2-1-R, including FEDER funds and by the Aragon Regional Government. ; Peer Reviewed

3 páginas, 3 figuras.-- et al. ; Epitaxial discontinuous Fe/MgO multilayers have been grown by pulsed laser deposition on MgO(001) single-crystal substrates. The multilayers with 0.6 nm nominal Fe layers thickness are superparamagnetic and demonstrate tunneling magnetoresistance (TMR) in the current-in-plane configuration. Increasing deposition temperature causes an improvement in crystal quality and is accompanied by higher TMR ratios. The maximum value (9.2% TMR at room temperature and 18 kOe magnetic field) trebles that of polycrystalline samples deposited simultaneously on glass substrates. A model formula for TMR ratio that includes both spin-dependent tunneling and spin-filtering effect is proposed to explain these results. ; Financial support by Spanish Ministry of Science (through project No. MAT2008-06567-C02 including FEDER funding) and by the Aragón Regional Government (through projects E26 and PI059/08) is acknowledged. Work of A.V. and G.N.K. was supported by Portuguese FCT through "Ciencia 2008" and "Ciencia 2007" programs, respectively. ; Peer reviewed

4 pages, 3 figures. ; We have investigated the transport and magnetotransport properties in Fe/MgO multilayers around the Fe percolation threshold as a function of the temperature and the nominal thickness of iron layer (t). Electrical resistivity measurements allowed us to disclose the charge transport mechanisms involved, which are closely related to the degree of discontinuity in the Fe layers. The samples with Fe thickness below percolation threshold (t ∼ 0.8 nm) exhibit isotropic magnetoresistance (MR), which can be understood considering spin-polarized electron tunneling between nanometer-sized, superparamagnetic Fe grains. The MR ratio increases with decreasing temperature from ∼ 3% at room temperature to ∼ 10% at 30 K. The temperature dependence of MR can be explained satisfactorily in terms of a modified Mitani's model. ; Financial support by Spanish Ministry of Science (through Project Nos. MAT2008-06567-C02 and CIT- 420000-2008-19 including FEDER funding) and by the Aragón Regional Government (through Project Nos. E26 and PI059/08) is acknowledged. ; Peer reviewed

Under the terms of the Creative Commons Attribution 3.0 Unported License.-- et al. ; Direct observation of domain wall (DW) nucleation and propagation in focused electron beam induced deposited Co nanowires as a function of their dimensions was carried out by Lorentz microscopy (LTEM) upon in situ application of magnetic field. Optimal dimensions favoring the unambiguous DW nucleation/propagation required for applications were found in 500-nm-wide and 13-nm-thick Co nanowires, with a maximum nucleation field and the largest gap between nucleation and propagation fields. The internal DW structures were resolved using the transport-of-intensity equation formalism in LTEM images and showed that the optimal nanowire dimensions correspond to the crossover between the nucleation of transverse and vortex walls. ; This work was supported by Spanish Ministry of Economy and Competitivity through project Nos. MAT2011-28532-C03-01, MAT2011-28532-C03-02, and MAT2011-27553-C02, including FEDER funds, by Junta de Castilla y Leon through the Project SA163A12, and by the European Union Seventh Framework Programme under Grant Agreement 312483—ESTEEM2 (Integrated Infrastructure Initiative—I3) and TRAIN2 project. ; Peer Reviewed

et al. ; Epitaxial films of SrMnO3 and bilayers of SrMnO3/La0.67Sr0.33MnO3 have been deposited by pulsed laser deposition on different substrates, namely, LaAlO3 (001), (LaAlO3)0.3(Sr2AlTaO6)0.7 (001), and SrTiO3 (001), allowing us to perform an exhaustive study of the dependence of antiferromagnetic order and exchange bias field on epitaxial strain. The Néel temperatures (TN) of the SrMnO3 films have been determined by low-energy muon spin spectroscopy. In agreement with theoretical predictions, TN is reduced as the epitaxial strain increases. From the comparison with first-principles calculations, a crossover from G-type to C-type antiferromagnetic orders is proposed at a critical tensile strain of around 1.6±0.1%. The exchange bias (coercive) field, obtained for the bilayers, increases (decreases) by increasing the epitaxial strain in the SrMnO3 layer, following an exponential dependence with temperature. Our experimental results can be explained by the existence of a spin-glass (SG) state at the interface between the SrMnO3 and La0.67Sr0.33MnO3 films. This SG state is due to the competition between the different exchange interactions present in the bilayer and favored by increasing the strain in the SrMnO3 layer. ; This work was supported by the Spanish Ministerio de Economía y Competitividad through Project Nos. MAT2011-28532-C03-02, MAT2011-27553-C02, MAT2012- 38213-C02-01, and MAT2014-51982-C2 including FEDER funding, by the Aragon Regional Government through projects E26 and CTPP4/11 and by the European Union under the Seventh Framework Programme under a contract for an Integrated Infrastructure Initiative Reference 312483-ESTEEM2. N. Marcano acknowledges the support of the Centro Universitario de la Defensa en Zaragoza (through Project 2013-03). ; Peer Reviewed