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This article is part of the themed collection: Recent Open Access Articles, A metal–insulator transition is observed in spin–orbit-coupled IrO2 thin films upon reduction of the film thickness. In the epitaxially grown samples, the critical thickness (t ∼ 1.5–2.2 nm) is found to depend on growth orientation (001), (100) or (110). Interestingly from the applied point of view, the insulating behavior is found even in polycrystalline ultrathin films. By analyzing the experimental electrical response with various theoretical models, we find good fits to the Efros–Shklovskii-VRH and the Arrhenius-type behaviors, which suggests an important role of electron correlations in determining the electrical properties of IrO2. Our magnetic measurements also point to a significant role of magnetic order. Altogether, our results would point to a mixed Slater- and Mott-type of insulator., This work was partially supported by the Spanish MINECO projects MAT2014-54425-R (MINECO/FEDER, UE), MAT2017-82970-C2-R (AEI/FEDER, UE), MAT2017-83468-R (AEI/FEDER, UE), MAT2017-87134-C02-01-R (AEI/FEDER, UE) and MAT2017-87134-C02-02-R (AEI/FEDER, UE), the Spanish MICINN project PID2020-115159GB-I00 / AEI / 10.13039/501100011033 and by the Aragon Regional Government (Projects No. E12-20R and E28-20R). E. A-E acknowledges the Spanish MINECO and the European Social Fund for an FPI (Formación de Personal Investigador, 2015) grant. R. B. acknowledges funding support from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement no. 665919. This research used resources of the APS, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We acknowledge Diamond Light Source for time on I20-Scanning under Proposal SP-17266. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation Horizon 2020. The authors acknowledge funding from the project Quantox of QuantERA ERA-NET Cofund of Quantum Technologies (Grant Agreement No. 731473) implemented within the European Union's Horizon 2020 Programme.

Spin transport is crucial for future spintronic devices operating at bandwidths up to the terahertz range. In F|N thin-film stacks made of a ferromagnetic/ferrimagnetic layer F and a normal-metal layer N, spin transport is mediated by (1) spin-polarized conduction electrons and/or (2) torque between electron spins. To identify a crossover from (1) to (2), we study laser-driven spin currents in F|Pt stacks where F consists of model materials with different degrees of electrical conductivity. For the magnetic insulators yttrium iron garnet, gadolinium iron garnet (GIG) and γ−Fe2O3, identical dynamics is observed. It arises from the terahertz interfacial spin Seebeck effect (SSE), is fully determined by the relaxation of the electrons in the metal layer, and provides a rough estimate of the spin-mixing conductance of the GIG/Pt and γ−Fe2O3/Pt interfaces. Remarkably, in the half-metallic ferrimagnet Fe3O4 (magnetite), our measurements reveal two spin-current components with opposite direction. The slower, positive component exhibits SSE dynamics and is assigned to torque-type magnon excitation of the A- and B-spin sublattices of Fe3O4. The faster, negative component arises from the pyrospintronic effect and can consistently be assigned to ultrafast demagnetization of minority-spin hopping electrons. This observation supports the magneto-electronic model of Fe3O4. In general, our results provide a route to the contact-free separation of torque- and conduction-electron-mediated spin currents., The authors acknowledge funding by the German Research Foundation through the collaborative research centers SFB TRR 227 “Ultrafast spin dynamics” (Project ID 328545488, projects A05, B02, and B03), SFB TRR 173 “Spin + X” (Project No. 358671374, projects A01 and B02), the European Union H2020 program through the project CoG TERAMAG(GrantNo.681917), the Spanish Ministry of Science and Innovation (Project No. PID2020-112914RB-I00), the National Natural Science Foundation of China (Grants No. 61988102 and No. 61975110), and the Czech Science Foundation through Project GA CR/Grant No. 21-28876J. P.J.-C. acknowledges the Spanish MECD for support through the FPU program (References No. FPU014/02546 and No. EST17/00382.)

Accessing the regime of coherent phonon propagation in nanostructures opens enormous possibilities to control the thermal conductivity in energy harvesting devices, phononic circuits, etc. In this paper we show that coherent phonons contribute substantially to the thermal conductivity of LaCoO3/SrTiO3 oxide superlattices, up to room temperature. We show that their contribution can be tuned through small variations of the superlattice periodicity, without changing the total superlattice thickness. Using this strategy, we tuned the thermal conductivity by 20% at room temperature. We also discuss the role of interface mixing and epitaxial relaxation as an extrinsic, material dependent key parameter for understanding the thermal conductivity of oxide superlattices., This work has received financial support from Ministerio de Economía y Competitividad (Spain) under project Nos. MAT2016-80762-R and PID2019-104150RB-I00, Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2019-2022, ED431G 2019/03), the European Union (European Regional Development Fund-ERDF), and the European Commission through the Horizon H2020 funding by H2020-MSCA-RISE-2016- Project No. 734187-SPICOLOST. E.L. is a Serra Húnter Fellow (Generalitat de Catalunya). D.B. acknowledges financial support from MINECO (Spain) through an FPI fellowship (BES-2017-079688). V.P. and A.O.F. were supported by the MINECO of Spain through the project PGC2018-101334-B-C21. A.O.F. thanks MECD for the financial support received through the FPU grant FPU16/02572.

We report the disentanglement of bulk and interfacial contributions to the thermally excited magnon spin current in the spin Seebeck effect under static heating. For this purpose, we have studied the dependence of the inverse spin Hall voltage and the thermal conductivity on the magnetic layer thickness. Knowledge of these quantities allows us to take into account the influence of both sources of thermal spin current in the analysis of the voltage dependence. The magnetic layer thickness modulates the relative magnitude of the involved thermal drops for a fixed total thermal difference throughout the sample. In the end, we attain the separate contributions of both sources of thermal spin current—bulk and interfacial—and obtain the value of the thermal magnon accumulation length scale in maghemite, which we find to be 29(1) nm. According to our results, bulk magnon accumulation dominates the spin Seebeck effect in our studied range of thicknesses, but the interfacial component is by no means negligible., This work was supported by the Spanish Ministry of Science [through Project Nos. MAT2014-51982-C2-R, MAT2016-80762-R, MAT2017-82970-C2-R, and PID2019-104150RB-I00 (including FEDER funding) and the Aragón Regional government (Project No. E26)]. P.J.-C. acknowledges Spanish MECD for support through FPU program (Reference No. FPU014/02546). D.B. acknowledges support from MINECO (Spain) through an FPI program (No. BES-2017-079688). R.R. also acknowledges support from the European Commission through the Project No. 734187-SPICOLOST (H2020-MSCA-RISE-2016), the European Union's Horizon 2020 research and innovation program through the Marie Sklodowska-Curie Actions Grant Agreement SPEC No. 894006, and the Spanish Ministry of Science (No. RYC 2019-026915-I). Authors acknowledge the Advanced Microscopy Laboratory-INA University of Zaragoza for offering access to their instruments. C. L-B. acknowledges Xunta de Galicia and ESF for a PhD Grant (ED481A-2018/013).

International audience; Spin Hall and Rashba–Edelstein effects, which are spin-to-charge conversion phenomena due to spin-orbit coupling (SOC), are attractingincreasing interest as pathways to manage rapidly and at low consumption cost the storage and processing of a large amount of data inspintronic devices as well as more efficient energy harvesting by spin-caloritronics devices. Materials with large SOC, such as heavy metals(HMs), are traditionally employed to get large spin-to-charge conversion. More recently, the use of graphene (gr) in proximity with largeSOC layers has been proposed as an efficient and tunable spin transport channel. Here, we explore the role of a graphene monolayer betweenCo and a HM and its interfacial spin transport properties by means of thermo-spin measurements. The gr/HM (Pt and Ta) stacks have beenprepared on epitaxial Ir(111)/Co(111) structures grown on sapphire crystals, in which the spin detector (i.e., top HM) and the spin injector(i.e., Co) are all grown in situ under controlled conditions and present clean and sharp interfaces. We find that a gr monolayer retains the spincurrent injected into the HM from the bottom Co layer. This has been observed by detecting a net reduction in the sum of the spin Seebeckand interfacial contributions due to the presence of gr and independent from the spin Hall angle sign of the HM used.Invited Paper published as part of the special topic on Emerging Materials for Spin-Charge Interconversion

Reversible structural transformations between perovskite (PV) ABO3−δ and brownmillerite (BM) ABO2.5 (A = Ca2+, Sr2+; B = Fe4+/3, Co4+/3+) oxides can be induced by topotactic oxygen exchange at moderate temperatures under reducing/oxidizing conditions. The combination of a large oxide-ion conductivity and a small free energy difference between the 4+/3+ oxidation states of many 3d transition metal ions enables these topotactic transformations. Herein, it is demonstrated that the electric field produced by a voltage-biased atomic force microscopy tip can induce such transformation between PV SrFeO3−δ and BM SrFeO2.5 at room temperature and with sub-micrometer spatial resolution. Interestingly, the structural transformation is kept after the electric field is removed, allowing a nonvolatile control of the local chemical, electrical, optical, and magnetic properties. Thus, the results presented in this paper open the door for the fabrication of stable ionic-based devices through the electric field patterning of different crystallographic phases.

Since the discovery of the spin Seebeck effect (SSE), much attention has been devoted to the study of the interaction between heat, spin, and charge in magnetic systems. The SSE refers to the generation of a spin current upon the application of a thermal gradient and detected by means of the inverse spin Hall effect. Conversely, the spin Peltier effect (SPE) refers to the generation of a heat current as a result of a spin current induced by the spin Hall effect. Here we report a strong enhancement of both the SSE and SPE in Fe3O4/Pt multilayered thin films at room temperature as a result of an increased thermo-spin conversion efficiency in the multilayers. These results open the possibility to design thin film heterostructures that may boost the application of thermal spin currents in spintronics., This work was supported by ERATO ‘Spin Quantum Rectification Project’ (Grant No. JPMJER1402) and PRESTO ‘Phase Interfaces for Highly Efficient Energy Utilization’ (Grant No. JPMJPR12C1) from JST, Japan; Grantin-Aid for Scientific Research (A) (Grant No. JP15H02012) and Grant-in-Aid for Scientific Research on Innovative Area, ‘Nano Spin Conversion Science’ (Grant No. JP26103005) from JSPS KAKENHI, Japan, the NEC Corporation, and the Noguchi Institute. The microscopy works were conducted in the Laboratorio de Microscopías Avanzadas at INA, Universidad de Zaragoza; H2020-MSCA-RISE-2016 SPICOLOST (Grant No. 734187); the Spanish Ministry of Economy and Competitiveness (Grant No. MAT2017-82970-C2, including FEDER), Spain; and the Aragón regional government (E26), Spain.

Oxide spinels of general formula AB2O4 (A = Mg2+, Fe2+; B = Al3+, Cr3+, etc.) constitute one of the most abundant crystalline structures in mineralogy. In this structure, cations distribute among octahedral and tetrahedral sites, according to their size and the crystal-field stabilization energy. The cationic arrangement determines the mechanical, magnetic, and transport properties of the spinel and can be influenced by external parameters like temperature, pressure, or epitaxial stress in the case of thin films. Here, we report a progressive change in the sign of the Poisson ratio, ν, in thin films of CoFe2O4, defining a smooth crossover from auxetic (ν < 0) to non-auxetic (ν > 0) behavior in response to epitaxial stress and temperature. Microstructural and magnetization studies, as well as ab initio calculations, demonstrate that such unusual elastic response is actually due to a progressive redistribution of Co2+ among the octahedral and tetrahedral sites of the spinel structure. The results presented in this work clarify a long standing controversy about the magnetic and elastic properties of Co-ferrites and are of general applicability for understanding the stress-relaxation mechanism in complex crystalline structures., This work has received financial support from Ministerio de Economía y Competitividad (Spain) under Project No. MAT2016-80762-R and MAT2017-82970-C2-R, Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2016-2019, No. ED431G/09), the European Union (European Regional Development Fund-ERDF), and the European Commission through the Horizon H2020 funding by H2020-MSCA-RISE-2016-Project No. 734187–SPICOLOST.

The hip fracture is one of the most common diseases for elder people and also, one of the most worrying one since it usually is the starting point of further complications for both, the health of the patient and their daily life. Additionally, reports shown that there exist differences between people living in different regions, thus limiting the use of global models. In this work we propose a hip fracture prediction tool for a local region, using clinical data of the population of that region. The data is processed with a dimensionality reduction tool in combination with and hyper-parametrization process and the corresponding hyper-parameter optimization process for obtaining good predictions in the diagnoses, as the results shown.

Reversible structural transformations between perovskite (PV) ABO3−δ and brownmillerite (BM) ABO2.5 (A = Ca2+, Sr2+; B = Fe4+/3, Co4+/3+) oxides can be induced by topotactic oxygen exchange at moderate temperatures under reducing/oxidizing conditions. The combination of a large oxide-ion conduc-tivity and a small free energy difference between the 4+/3+ oxidation states of many 3d transition metal ions enables these topotactic transformations. Herein, it is demonstrated that the electric field produced by a voltage-biased atomic force microscopy tip can induce such transformation between PV SrFeO3−δ and BM SrFeO2.5 at room temperature and with sub-micrometer spatial resolution. Interestingly, the structural transformation is kept after the electric field is removed, allowing a nonvolatile control of the local chemical, electrical, optical, and magnetic properties. Thus, the results presented in this paper open the door for the fabrication of stable ionic-based devices through the electric field patterning of different crystallographic phases., This work has received financial support from Ministerio de Economía y Competitividad (Spain) under Project Nos. MAT2016-80762-R, MAT2017-82970-C2-R, and PGC2018-101334-A-C22, Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2016-2019, ED431G/09), the European Union (European Regional Development Fund-ERDF), and the European Commission through the Horizon H2020 funding by H2020-MSCA-RISE-2016 under Project No. 734187-SPICOLOST. This project has received funding from the European’s Union Horizon 2020 research and innovation programme under Grant No. 823717-ESTEEM3.

We have studied the anomalous Nernst effect (ANE) in [Fe3O4/Pt]-based heterostructures grown at high temperature, by measuring the ANE-induced electric field with a magnetic field applied normal to the sample surface, in the perpendicular magnetized configuration, where only the ANEs from the ferromagnetic layers or magnetic proximity effects can be detected. An ANE voltage is observed for [Fe3O4/Pt]n multilayers, and we further investigated its origin by performing measurements in [Fe3O4/Pt/Fe3O4] trilayers as a function of the Pt thickness. Our results suggest the presence of an interface-induced ANE in the metallic layer, possibly driven by a heat induced subnanometer interdiffusion which affects the nature of the Fe3O4/Pt interface. Despite this ANE, the spin Seebeck effect is the dominant mechanism for the transverse thermoelectric voltage in the in-plane magnetized configuration, accounting for about 70% of the voltage in the multilayers., This work was supported by the ERATO “Spin Quantum Rectification Project” (Grant No. JPMJER1402) and PRESTO “Phase Interfaces for Highly Efficient Energy Utilization” (Grant No. JPMJPR12C1) from JST, Japan; Grant-in-Aid for Scientific Research (A) (Grant No. JP15H02012), Grant-in-Aid for Scientific Research on Innovative Area, “Nano Spin Conversion Science” (Grant No. JP26103005) and Grant-in-Aid for Research Activity Start-up (No. JP18H05841) from JSPS KAKENHI, Japan; H2020-MSCA-RISE-2016 SPICOLOST (Grant No. 734187); and the Spanish Ministry of Economy and Competitiveness (Grant No. MAT2017-82970-C2, including FEDER) and the Aragon regional government (E26), Spain. The microscopy works were conducted in the LMA at INA, Universidad de Zaragoza. A.A. acknowledges MINECO [through Project Nos. FIS2016-78591-C3-1-R (SKYTRON), PCIN-2015-111 (SOgraph), and SEV-2016-0686] and Comunidad de Madrid through Grant No. S2018/NMT-4321 (NANOMAGCOST-CM).

Single-phase and single-oriented epitaxial Cr2O3 thin film has been grown on SrTiO3 (1 1 1) substrate for the first time. The morphology, epitaxial growth mode and oxygen stoichiometry of the obtained film have been investigated by AFM, XRR, XRD and XPS, and compared to thin film grown on alfa-Al2O3 under equivalent conditions. The Cr2O3/SrTiO3 system presents a non-coincidence growth based on in&#-plane rotation of 30° of the Cr2O3 layer respect to the underlying SrTiO3 (1 1 1) substrate, while a coincidence growth based on axis-on-axis coupling is present for Cr2O3-Al2O3. However, in both cases an in-plane compression occurs in order to match the layer and substrate lattices. The formation of punctual defects in the form of oxygen vacancies have been observed by XPS for the layer grown on alfa-Al2O3, being the main mechanism for strain alleviation (4%). However, the 18 nm thick layer grown on SrTiO3 presents stoichiometric oxygen content maintaining an epitaxial strain (1.6%) accumulated on the lattice. Both epitaxial Cr2O3 layers show soft ferromagnetic response with coercive fields of 60 Oe and 90 Oe for the layer grown on SrTiO3 and alfa-Al2O3, respectively. The ESRF, MCIU and CSIC are acknowledged for the provision of synchrotron radiation facilities under Project No. PIE 2010-6-OE-013. This work has received financial support from Ministerio de Economía y Competitividad (Spain) under Project No. MAT2017-82970-C2-R and MAT2017-82970-C2-2-R. The microscopy works was conducted in the Laboratorio de Microscopías Avanzadas (LMA) at Instituto de Nanociencia de Aragón (INA)-Universidad de Zaragoza. The authors acknowledge the LMA-INA for offering access to their instruments and expertise. A. Prados would like to acknowledge the postdoctoral fellowship granted by Comunidad de Madrid and the European Union [PEJD-2016/IND-2233] and the use of facilities of Instituto de Sistemas Optoelectrónicos y Microtecnología (ISOM-UPM).

6 pags, 4 figs, The precise control and stabilization of magnetic domain walls is key for the development of the next generation magnetic nano-devices. Among the multitude of magnetic configurations of a magnetic domain wall, topologically protected states are of particular interest due to their intrinsic stability. In this work, using XMCD-PEEM, we have observed a topologically protected magnetic domain wall in a ferromagnetic cylindrical nanowire. Its structure is stabilized by periodic sharp alterations of the chemical composition in the nanowire. The large stability of this topologically protected domain wall contrasts with the mobility of other non-protected and non-chiral states also present in the same nanowire. The micromagnetic simulations show the structure and the conditions required to find the topologically protected state. These results are relevant for the design of future spintronic devices such as domain wall based RF oscillators or magnetic memories., This work is supported by the Spanish Ministry of Economy and Competitiveness (MINECO) through Projects MAT2014-52477-C5-1-P, 2-P, MAT2015-64110-C2-1-P, 2-P and MAT2017-87072-C4-2-P and by Portuguese FCT and COMPETE 2020, under project POCI-01-0145-FEDER-028676. IMDEA Nanociencia acknowledges support from the Severo Ochoa Programme for Centres of Excellence in R&D (MINECO, Grant SEV-2016-0686). MPP acknowledges FCT for grant SFRH/BPD/84948/2012. SRG acknowledges MINECO for FPI fellowship.

We report the fabrication of high crystal quality epitaxial thin films of maghemite (γ−Fe2O3), a classic ferrimagnetic insulating iron oxide. Spin Seebeck effect (SSE) measurements in γ−Fe2O3/Pt bilayers as a function of sample preparation conditions and temperature yield a SSE coefficient of 0.5(1) µV/K at room temperature. Dependence on temperature allows us to estimate the magnon diffusion length in maghemite to be in the range of tens of nanometers, in good agreement with that of conducting iron oxide magnetite (Fe3O4), establishing the relevance of spin currents of magnonic origin in magnetic iron oxides., This work was supported by the Spanish Ministry of Science (through Project Nos. MAT2014- 51982-C2-R and C1-R, including FEDER funding) and the Aragon Regional government (Project ´ No. E26). Pilar Jimenez-Cavero acknowledges Spanish MECD for support through FPU program ´ (Reference No. FPU014/02546). The authors acknowledge the Advanced Microscopy LaboratoryINA University of Zaragoza for offering access to their instruments. This work was supported by PRESTO “Phase Interfaces for Highly Efficient Energy Utilization” and ERATO “Spin Quantum Rectification” from JST, Japan, Grant-in-Aid for Scientific Research (A) (No. 15H02012), Grant-inAid for Scientific Research on Innovative Area, “Nano Spin Conversion Science” (No. 26103005) from MEXT, Japan, NEC Corporation, and the Noguchi Institute.

We report the fabrication of epitaxial Y3Fe5O12 (YIG) thin films on Gd3Ga5O12 (111) using a chemical solution method. Cubic YIG is a ferrimagnetic material at room temperature, with excellent magneto-optical properties, high electrical resistivity, and a very narrow ferromagnetic resonance, which makes it particularly suitable for applications in filters and resonators at microwave frequencies. But these properties depend on the precise stoichiometry and distribution of Fe3+ ions among the octahedral/tetrahedral sites of a complex structure, which hampered the production of high-quality YIG thin films by affordable chemical methods. Here we report the chemical solution synthesis of YIG thin films, with excellent chemical, crystalline, and magnetic homogeneity. The films show a very narrow ferromagnetic resonance (long spin relaxation time), comparable to that obtained from high-vacuum physical deposition methods. These results demonstrate that chemical methods can compete to develop nanometer-thick YIG films with the quality required for spintronic devices and other high-frequency applications., This work was supported by the Ministry of Science of Spain (Projects No. MAT2016-80762-R, MAT2017-82970-C2-R, and No. MAT2014-51982-C2), the Consellería de Cultura, Educación e Ordenación Universitaria, Xunta de Galicia (ED431F 2016/008, and Centro Singular de Investigación de Galicia Accreditation 2016–2019, ED431G/09), the European Regional Development Fund (ERDF), and the Aragón Regional Government through Projects E26. The microscopy works have been conducted in the Laboratorio de Microscopías Avanzadas (LMA) at Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza. The authors acknowledge the LMA-INA for offering access to their instruments and expertise. Pilar Jiménez-Cavero acknowledges Spanish MECD for support through FPU program (Reference No. FPU014/02546).

(Co(0.4 nm)/Pt(0.7 nm)) (x = 10, 20, 30) multilayer antidot thin films (films with arrays of nanoholes) have been grown by dc sputtering onto self-assembled pores of anodic alumina membranes with a tailored diameter and a fixed inter-hole distance. The magnetic behavior has been quantified by vibrating sample magnetometry, and the surface magnetization patterns have been imaged by magnetic force microscopy. The magnetization reversal mechanism is characterized by two steps depending on the film thickness and antidot diameter. These steps are ascribed to the nucleation and demagnetization of magnetic stripe domains. Their presence confirms the perpendicular anisotropy of the multilayer antidot films. The coercivity of antidot thin film is larger than that of the continuous films due to additional pinning centers provided by antidots. The width of the stripe domains increases as a function of film thickness. The demagnetization is further investigated through micromagnetic simulations that are in agreement with the measured hysteresis loops and their features. Different reversal mechanisms and an increase of the domain width in antidot thin films are also confirmed as a function of the magnetic anisotropy, antidot diameter and thickness of the thin film. The presence of antidots with a designed geometry is revealed to be successful in tailoring the coercivity of the thin films and magnetic patterns, which is relevant for advances in nanoscale technologies., The work has been supported by the Spanish Ministry of Science and Innovation under projects MAT2013-48054-C2-1-R and MAT2013-47078-C2-2-P.

We report temperature dependent measurements of the spin Seebeck effect (SSE) in multilayers formed by repeated growth of a FeO/Pt bilayer junction. The magnitude of the observed enhancement of the SSE, relative to the SSE in the single bilayer, shows a monotonic increase with decreasing the temperature. This result can be understood by an increase of the characteristic length for spin current transport in the system, in qualitative agreement with the recently observed increase in the magnon diffusion length in FeO at lower temperatures. Our result suggests that the thermoelectric performance of the SSE in multilayer structures can be further improved by careful choice of materials with suitable spin transport properties., This work was supported by the Spanish Ministry of Science (through projects MAT2014-51982-C2-R, including FEDER funding), the Aragón Regional Government (project E26), Thermo-spintronic Marie-Curie CIG (Grant Agreement No. 304043), JST-PRESTO “Phase Interfaces for Highly Efficient Energy Utilization” from JST, Japan, Grant-in-Aid for Scientific Research on Innovative Areas “Nano Spin Conversion Science” (26103005), Grant-in-Aid for Scientific Research (A) (15H02012) from MEXT, Japan, NEC Corporation, and The Noguchi Institute. T.K. is supported by JSPS through a research fellowship for young scientists (15J08026).

Epitaxial strain alters the physical properties of thin films grown on single crystal substrates. Thin film oxides are particularly apt for strain engineering new functionalities in ferroic materials. In the case of La2/3Ca1/3MnO3 (LCMO) thin films, here we show the first experimental images obtained by electron holography demonstrating that epitaxial strain induces the segregation of a flat and uniform nonferromagnetic layer with antiferromagnetic (AFM) character at the top surface of a ferromagnetic (FM) layer, the whole film being chemical and structurally homogeneous at room temperature. For different substrates and growth conditions the tetragonality of LCMO at room temperature, defined as τ = |c – a|/a, is the driving force for a phase coexistence above an approximate critical value of τC ≈ 0.024. Theoretical calculations prove that the increased tetragonality changes the energy balance of the FM and AFM ground states in strained LCMO, enabling the formation of magnetically inhomogeneous states. This work gives the key evidence that opens a new route to synthesize strain-induced exchanged-biased FM–AFM bilayers in single thin films, which could serve as building blocks of future spintronic devices., This work was supported by Spanish Ministry of Science through projects No. MAT2011-28532-C03-02 and MAT2011-27553-C02 including FEDER funding, by the Aragon Regional Government through projects E26 and CTPP4/11, by the Universidad de Zaragoza through the contract PIF-UZ-2009-CIE-02, and by the European Union under the Seventh Framework Programme under a contract for an Integrated Infrastructure Initiative Reference 312483-ESTEEM2.

We report magnetic and electronic transport measurements across epitaxial bilayers of ferromagnetic insulator LaCoO3 and half-metallic ferromagnet La2/3Sr1/3MnO3 (LCO/LSMO: 3.5 nm/20 nm) fabricated by a chemical solution method. The I–V curves at room temperature and 4K measured with conducting atomic force microscopy (CAFM) on well-defined patterned areas exhibit the typical features of a tunneling process. The curves have been fitted to the Simmons model to determine the height (φ) and width (s) of the insulating LCO barrier. The results yield φ = 0.40 ± 0.05 eV (0.50 ± 0.01 eV) at room temperature (4K) and s = 3 nm, in good agreement with the structural analysis. Our results demonstrate that this chemical method is able to produce epitaxial heterostructures with the quality required for this type of fundamental studies and applications.

The magnetic properties of CoP electrodeposited alloys can be easily controlled by layering the alloys and modulating the P content of the different layers by using pulse plating in the electrodeposition process. However, because of its amorphous nature, the study of the interface quality, which is a limitation for the optimization of the soft magnetic properties of these alloys, becomes a complex task. In this work, we use Rutherford backscattering spectroscopy (RBS) to determine that electrodeposited Co0.74P0.26/Co0.83P0.17 amorphous multilayers with layers down to 20 nm-thick are composed by well-defined layers with interfacial roughness below 3 nm. We have also determined, using magnetostriction measurements, that 4 nm is the lower limitation for the layer thickness. Below this thickness, the layers are mixed and the magnetic behavior of the multilayered films is similar to that shown by single layers, thus going from in-plane to out-of-plane magnetic anisotropy. Therefore, these results establish the range in which the magnetic properties of these alloys can be controlled by layering.

This work reports the fabrication and characterization of Langmuir–Blodgett films of nanoparticles (size 51 ± 10 nm) of the metal organic framework MIL-101(Cr). LB film characterization by SEM, UV–vis, GIXRD, and QCM has shown that the addition of 1 wt % of behenic acid to MOF dispersion allows obtaining dense monolayers at the air–water interface that can be deposited onto solid substrates of different nature with transfer ratios close to 1. Moreover, a QCM-based setup has been built and used for the first time to measure CO2 adsorption isotherms at 303 K on MOF LB films, proving that LB films with MOF masses between 1.2 (1 layer) and 2.3 (2 layers) μg can be used to obtain accurate adsorption values at 100 kPa, similar to those obtained by conventional adsorption methods that require much larger MOF quantities (tens of milligrams).

We report the effect of interface symmetry-mismatch on the magnetic properties of LaCoO3 (LCO) thin films. Growing epitaxial LCO under tensile strain on top of cubic SrTiO3 (STO) produces a contraction along the c axis and a characteristic ferromagnetic response. However, we report here that ferromagnetism in LCO is completely suppressed when grown on top of a buffer layer of rhombohedral La2/3Sr1/3MnO3 (LSMO), in spite of identical in-plane and out-of-plane lattice deformation. This confirms that it is the lattice symmetry mismatch and not just the total strain, which determines the magnetism of LCO. On the basis of this control over the magnetic properties of LCO, we designed a multilayered structure to achieve independent rotation of the magnetization in ferromagnetic insulating LCO and half-metallic ferromagnet LSMO. This is an important step forward for the design of spin-filtering tunnel barriers based on LCO.

The dependence of Spin Seebeck effect (SSE) with the thickness of the magnetic materials is studied by means of incoherent thermal excitation. The SSE voltage signal in Fe3O4/Pt bilayer structure increases with the magnetic material thickness up to 100 nm, approximately, showing signs of saturation for larger thickness. This dependence is well described in terms of a spin current pumped in the platinum film by the magnon accumulation in the magnetic material. The spin current is generated by a gradient of temperature in the system and detected by the Pt top contact by means of inverse spin Hall effect. Calculations in the frame of the linear response theory adjust with a high degree of accuracy the experimental data, giving a thermal length scale of the magnon accumulation (Λ) of 17 ± 3 nm at 300 K and Λ = 40 ± 10 nm at 70 K., This work was supported by the Spanish Ministry of Science (through Project No. MAT2014-51982-C2-R, including European social fund), the Aragon Regional government (Project No. E26), and Thermo-Spintronic Marie Curie CIG Project (Grant Agreement No. 304043).

All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license.-- et al., We report a systematic study on the thermoelectric performance of spin Seebeck devices based on Fe3O4/Pt junction systems. We explore two types of device geometries: a spin Hall thermopile and spin Seebeck multilayer structures. The spin Hall thermopile increases the sensitivity of the spin Seebeck effect, while the increase in the sample internal resistance has a detrimental effect on the output power. We found that the spin Seebeck multilayers can overcome this limitation since the multilayers exhibit the enhancement of the thermoelectric voltage and the reduction of the internal resistance simultaneously, therefore resulting in significant power enhancement. This result demonstrates that the multilayer structures are useful for improving the thermoelectric performance of the spin Seebeck effect., This work was supported by the Spanish Ministry of Science (through Project Nos. PRI-PIBJP-2011-0794 and MAT2011-27553-C02, including FEDER funding), the Aragón Regional Government (Project No. E26), Thermo-spintronic Marie-Curie CIG (Grant Agreement No. 304043), JST-PRESTO “Phase Interfaces for Highly Ecient Energy Utilization” from JST, Japan, Grant in-Aid for Scientific Research on Innovative Areas “Nano-Spin Conversion Science” (Grant No. 26103005), Grant-in-Aid for Challenging Exploratory Research (Grant No. 26600067), Grant-inAid for Scientific Research (A) (Grant No. 15H02012) from MEXT, Japan, NEC Corporation, and The Noguchi Institute.

The spin Hall effect (SHE) provides an efficient tool for the production of pure spin currents, essentially for the next generation of spintronics devices. Giant SHE has been reported in Cu doped with 0.5% Bi grown by sputtering, and larger values are predicted for larger Bi doping. In this work, we demonstrate the possibility of doping Cu with up to 10% of Bi atoms without evidence of Bi surface segregation or cluster formation. In addition, YIG/BiCu structures have been grown, showing a spin mixing conductance larger that the one shown by similar Pt/YIG structures, reflecting the potentiality of these new materials., This work has been partially funded by MAT2014-52477-C5, MAT2017-87072-C4, and MAT2015-64110-C2-2-P from the Ministerio de Ciencia e Innovacion and Nanofrontmag from ´ Comunidad de Madrid. IMDEA Nanociencia acknowledges support from the Severo Ochoa Programme for Centres of Excellence in R&D (MINECO, Grant No. SEV-2016-0686).

Mechanically resonant ferromagnetic MEMS sensors intended for magnetic field gradient measurements are presented. Suspended quad-beams with proof mass have been designed to improve their sensitivity and to simplify the detection. Fabricated devices exhibit the compact size of current MEMS technologies and are built within a simple deep-reactive-ion etching-based process. Nanometer-resolution detection based on optical interferometry and signal processing techniques have been employed to find out dynamic-mode transformation factors of 6.25 × 10−3 T/m/Hz with 0.1-Hz resolution. The device performs in situ gradiometry with a single-sensor structure, which represents a technological advance to current-art gradiometers. Peerreview

Spin Seebeck effects (SSEs) have been investigated in highly crystalline magnetic multilayer [Fe3O4/Pt]n films. Voltage as well as power generated by the SSE were found to be significantly enhanced with increasing the number of layers n. This voltage enhancement defies the simple understanding of the SSE and suggests that spin current flowing between the magnetic layers in the thickness direction plays an important role in multilayer SSE systems and the observed voltage enhancement.

Under the terms of the Creative Commons Attribution 3.0 Unported License to their work., We show here that using spin orbit coupling interactions at a metallic interface it is possible to control the sign of the spin to charge conversion in a spin pumping experiment. Using the intrinsic symmetry of the “Inverse Rashba Edelstein Effect” (IREE) in a Bi/Ag interface, the charge current changes sign when reversing the order of the Ag and Bi stacking. This confirms the IREE nature of the conversion of spin into charge in these interfaces and opens the way to tailoring the spin sensing voltage by an appropriate trilayer sequence., We would like to acknowledge financial support from the European Commission through the Marie Curie Intra European Fellowship Project No. 301656: AtomicFMR, funded by the 7th Framework Programme. This work was supported by Spanish Ministry of Economy and Competitivity through Project No. MAT2011-27553-C02, including FEDER funds, and by the Aragon Regional Government.

In this paper we present an analytical model for describing the sensitivity of a toroidal fluxgate sensor. The model is based on a simplified schematics for the hysteresis loop of the fluxgate core that only includes the coercivity, the saturation field and the saturation magnetization. In spite of this simplicity, the model has been successfully used to describe the variation of the sensitivity of a PCB-based fluxgate sensor with the amplitude and the frequency of the driving current. The model has been developed for a toroidal configuration but can be easily modified to describe other geometries.

CoP alloys have been electrodeposited at room temperature from electrolytes with different pH values and their magnetic properties have been studied. Cracks and fractures appear when using stiff substrates, showing that high internal stresses, due to hydrogen evolution, are involved in the electrodeposition process. Samples electrodeposited onto flexible substrates do not show cracks on the surface. We also report an increment in the coercivity of the alloys when the pH of the electrolyte decreases, and therefore, the hydrogen evolution and the internal stresses increase.

We report magnetic and electronic transport measurements across epitaxial bilayers of ferromagnetic insulator LaCoO3 and half-metallic ferromagnet La2/3Sr1/3MnO3 (LCO/LSMO: 3.5 nm/20 nm) fabricated by a chemical solution method. The I-V curves at room temperature and 4K measured with conducting atomic force microscopy (CAFM) on well-defined patterned areas exhibit the typical features of a tunneling process. The curves have been fitted to the Simmons model to determine the height (φ) and width (s) of the insulating LCO barrier. The results yield φ = 0.40 ± 0.05 eV (0.50 ± 0.01 eV) at room temperature (4K) and s = 3 nm, in good agreement with the structural analysis. Our results demonstrate that this chemical method is able to produce epitaxial heterostructures with the quality required for this type of fundamental studies and applications.

We report a complete characterization of the anomalous Nernst effect (ANE) and its relationship with the anomalous Hall effect (AHE) in ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$. By combining full thermoelectric and electric transport measurements as a function of temperature, we have verified that the universal scaling relation between the anomalous Hall and diagonal conductivities (${\ensuremath{\sigma}}_{zy}\ensuremath{\propto}{\ensuremath{\sigma}}_{zz}^{1.6}$), observed in materials with bad-metal-hopping type of conduction, is also applicable to the thermoelectric transport. We further show that the ANE and AHE are commonly related through the Mott relation, therefore demonstrating its validity for anomalous transport phenomena in materials with conduction in the the dirty regime.

We present a comparative study of the anomalous Nernst effect (ANE), measured at room temperature for magnetite thin films deposited on different substrates in order to study the effects induced by the substrate, compressive or tensile strain and structural defects as anti-phase boundaries (APB), on the observed ANE. From our preliminary results we have observed an increase of the measured ANE in the case of compressive strain compared with the tensile one. Moreover our results also suggest that the density of APBs also play an important role in the ANE values.

Under the terms of the Creative Commons Attribution 3.0 Unported License to their work.-- et al., We report the experimental observation of the spin Seebeck effect in magnetite thin films. The signal observed at temperatures above the Verwey transition is a contribution from both the anomalous Nernst (ANE) and spin Seebeck (SSE) effects. The contribution from the ANE of the Fe3O 4 layer to the SSE is found to be negligible due to the resistivity difference between Fe3O4 and Pt layers. Below the Verwey transition, the SSE is free from the ANE of the ferromagnetic layer and it is also found to dominate over the ANE due to magnetic proximity effect on the Pt layer. © 2013 American Institute of Physics., This work was supported by the Spanish Ministry of Science (through projects PLE2009-0017, PRI-PIBJP-2011-0794, MAT2011-27553-C02, including FEDER funding) and the Aragón Regional Government (project E26). This research was supported by Strategic International Cooperative Program, Japan Science and Technology Agency (JST), PRESTO-JST “Phase Interfaces for Highly Efficient Energy Utilization,” CREST-JST “Creation of Nanosystems with Novel Functions through Process Integration,” a Grant-in-Aid for Research Activity Start-up (24860003) from MEXT, Japan, a Grant-in-Aid for Scientific Research (A) (24244051) from MEXT, Japan, LC-IMR of Tohoku University, the Murata Science Foundation, and the Mazda Foundation.

The dynamic properties of membranes have been object of many researches since they can be used as sensor heads in different devices. Some methods have been proposed to solve the problem of determining the resonance frequencies and their dependence on the stress caused by forces applied on the membrane surface. The problem of the vibrating rectangular membrane under a stress caused by a uniform in-plane force is well known. However, the resonance frequency behaviour when the force is out-of-plane instead of in-plane, is not so well understood and documented. A gradiometer which uses a silicon square membrane with a magnet fixed on it as a sensor head has been developed in a previous work. This device reports a quadratic dependence of the frequency on the out-of-plane magnetic force. In this work, simulations to obtain the dependence of the frequency of the fundamental flexural mode on the stress have been performed. It has been studied the influence of in-plane and out-of-plane forces applied to the membrane. As expected, a square root dependence has been found for in-plane forces. Nevertheless, the problem is more complex when out-of plane forces are considered. Out-of-plane forces gives rise to an initial quadratic dependence which turns into a square root dependence from a certain stress value. The quadratic range increases and the rate of change of the frequency decreases as the surface of the magnet fixed on the membrane increases. The study has addressed these problems and both, experimental and simulated results have been compared and a good agreement between experimental and simulated results has been found, 14 pages, 10 figures

The biaxially textured growth of superconducting Co-doped BaFe2As2 (Ba-122) thin films has been realized on ion beam assisted deposition (IBAD) MgO coated conductor templates by employing an iron buffer architecture. The iron pnictide coated conductor showed a superconducting transition temperature of 21.5 K, which is slightly lower than that of Co-doped Ba-122 films on single crystalline MgO substrates. A self-field critical current density of over 105 Acm-2 has already been achieved even at 8 K. The current experiment highlights the potential of possible coated conductor applications of the iron-based superconductors.