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Narrow bandgap ferroelectrics are receiving a renewed interest for photovoltaic applications aiming at exploiting new functionalities arising from bulk photovoltaic effect (BPE). We report on the photovoltaic response of vertical capacitors of ferroelectric hexagonal LuMnO3 films sandwiched between semitransparent top electrodes (Pt, Co, Ti) and a common bottom (Pt) bottom electrode. Our results show that the presence of electrodes, other than their optical transmittance, crucially determines the imprint in the ferroelectric layer and ultimately the sensitivity of short circuit current density (Jsc) to the ferroelectric polarization direction. The use of ultrathin (7 nm) Pt top electrodes allowed to obtain a large Jsc (up to 100 mA/cm2) and an open circuit voltage of Voc ≈ 0.52 V, with a responsivity of 2 × 10−3 A/W. Yet, polarization back-switching due to imprint largely washes out the dependence of Jsc on the direction of the polarization and thus, at first sight, Jsc seemingly appears to be ruled by conventional photovoltaic response. However, a pioneering analysis of the light-polarization dependent photosensitivity, allowed to disentangle for the first time, a genuine contribution of BPE from a ubiquitous Fresnel-like contribution arising from interfaced optical media., Financial support from the Spanish Ministry of Science, Innovation and Universities, through the “Severo Ochoa” Programme for Centers of Excellence in R&D (FUNFUTURE CEX2019-000917-S), MAT2017-85232-R (AEI/FEDER, EU) and PID2019-107727RB-I00 (MINECO/FEDER, EU) projects, and from Generalitat de Catalunya (2017 SGR 1377) is acknowledged. I. F. acknowledges RyC Contract RYC-2017-22531. Project supported by a 2020 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation. ICTS-CNME at UCM is acknowledged for offering access to STEM microscopy and expertise. A. Q. acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities through the Juan de la Cierva formación contract (FJC2019-039780-I). Y. S. and H. T. are financially supported by China Scholarship Council (CSC) with No. 201806410010 and No. 201906050014, respectively. The work of Y. S. and H. T. has been done as a part of their Ph.D. program in Materials Science at Universitat Autònoma de Barcelona., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

Defects in crystalline structures play a vital role in their properties, so their proper characterization is essential to understanding and improving the behaviour of the materials. In this work, their presence in Ca4Fe9O17 has been analysed. Its structure exhibits three different iron coordination topologies and can be described as layers of corner-sharing FeO5 bipyramids stacked along the c axis together with layers of edge-sharing FeO6 octahedra, both being linked by FeO4 tetrahedra. The relative position of the FeO4 tetrahedra generates three possible stacking directions, which results in stacking faults when more than one is combined. Structural refinement using the Rietveld method in X-ray and neutron powder diffraction data was not possible due to significant mismatches between the observed and calculated integrated intensities for several peaks resulting from this atomic disorder. Selected area electron diffraction (SAED) and high-resolution scanning transmission electron microscopy (HR-STEM) images confirm the local defective nature of the material. The FAULTS software enabled a successful refinement of the structure considering a high concentration of planar defects, conferred by the existence of three possible stacking directions in the crystal structure, all of them confined in the basal plane., We acknowledge beamtime at ALBA synchrotron (proposal 2019073634) and ILL (EASY access system) and Dr François Fauth and Dr Clemens Ritter, respectively, for their help during data collection. ICMAB authors acknowledge Spain's Agencia Estatal de Investigación Severo Ochoa Program for Centers of Excellence in R&D (CEX2019-000917-S) and funding through grant PID2020-113805GB-I00. ICTS-CNME at UCM is acknowledged for offering access to STEM microscopy and expertise., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

Multifunctional magnetic nanocomposites based on mesoporous silica have a wide range of potential applications in catalysis, biomedicine, or sensing. Such particles combine responsiveness to external magnetic fields with other functionalities endowed by the agents loaded inside the pores or conjugated to the particle surface. Different applications might benefit from specific particle morphologies. In the case of biomedical applications, mesoporous silica nanospheres have been extensively studied while nanorods, with a more challenging preparation, have attracted much less attention despite the positive impact on the therapeutic performance shown by seminal studies. Here, we report on a sol-gel synthesis of mesoporous rodlike silica particles of two distinct lengths (1.4 and 0.9 μm) and aspect ratios (4.7 and 2.2) using Pluronic P123 as a structure-directing template and rendering ∼1 g of rods per batch. Iron oxide nanoparticles have been synthesized within the pores yielding maghemite (γ-Fe2O3) nanocrystals of elongated shape (∼7 nm × 5 nm) with a [110] preferential orientation along the rod axis and a superparamagnetic character. The performance of the rods as T2-weighted MRI contrast agents has also been confirmed. In a subsequent step, the mesoporous silica rods were loaded with a cerium compound and their surface was functionalized with fluorophores (fluorescamine and Cyanine5) emitting at λ = 525 and 730 nm, respectively, thus highlighting the possibility of multiple imaging modalities. The biocompatibility of the rods was evaluated in vitro in a zebrafish (Danio rerio) liver cell line (ZFL), with results showing that neither long nor short rods with magnetic particles caused cytotoxicity in ZFL cells for concentrations up to 50 μg/ml. We advocate that such nanocomposites can find applications in medical imaging and therapy, where the influence of shape on performance can be also assessed., The authors acknowledge financial support from the Spanish Ministry of Science and Innovation through the RTI2018-096273-B-I00 project, the ‘Severo Ochoa’ Programme for Centers of Excellence in R&D (CEX2019-000917-S). The Generalitat de Catalunya, project 2017SGR765, is also acknowledged. This research work was performed in the framework of the Nanomedicine CSIC HUB (ref 202180E048).The authors participate in the Aerogels COST ACTION (CA 18125). J.G. received financial support through the “la Caixa” INPhINIT Fellowship Grant for Doctoral Studies at Spanish Research Centers of Excellence (Grant code: LCF/BQ/DI17/11620041), “la Caixa” Banking Foundation (ID100010434), Barcelona, Spain. J.G. was enrolled in the doctoral program in Materials Science at the UAB. M.T. (ref RYC2019-026841-I) has a post-doctoral fellowship “Ramón y Cajal” supported by the “Ministerio de Ciencia e Innovación”, Spanish Government. A. G. has been supported by the fellowship from Instituto de Salud Carlos III with FEDER funds (FI17/00073). A.Rosell and A. G. work takes part within the RETICS-INVICTUS PLUS from Instituto de Salud Carlos III with FEDER funds (RD16/0019/0021). G. Antorrena from the LMA at Universidad de Zaragoza is acknowledged for performing XPS measurements. ICTS-CNME at UCM is also acknowledged for offering access to STEM and expertise. The ICMAB Scientific services of electron microscopy, low temperatures and magnetometry, thermal analysis, and X-ray diffraction have performed measurements for the present work. Nico Dix, Joan Esquius, and Xavi Campos are acknowledged by making possible SAXS measurements at the ICMAB X-ray diffraction service.

Literature is rich on the study of different strategies to tailor ferroelectric properties of HfO2. Among them, chemical doping is the most studied. La doped HfO2 films have attracted interest because they show very low leakage current and high endurance. On the other hand, stress controlled by substrate selection has shown to induce ferroelectric properties variations in Hf0.5Zr0.5O2 films. Here, we investigate stress effects in La-doped epitaxial HfO2 films. Interestingly, ferroelectricity is measured in films grown on substrates having a broad range of lattice parameter from 3.71 to 4.21 Å. While comparing the obtained results with those obtained in epitaxial Hf0.5Zr0.5O2, it is observed that La doped HfO2 shows always larger remanent polarization (Pr) if the same substrate is used. Films grown on substrates with large lattice parameter (TbScO3 and GdScO3) show very large values of remanent polarization (29 μC/cm2), but it is also noticeable that the films on substrates with small parameter (YAlO3) show remanent polarization above 5 μC/cm2, whereas negligible Pr was detected in equivalent Hf0.5Zr0.5O2 films. Therefore, chemical doping and epitaxial stress do not compete and can be both used to synergetically tailor ferroelectric properties and eventually improve them., Financial support from the Spanish Ministry of Science and Innovation (MCIN/AEI/ 10.13039/501100011033), through the Severo Ochoa FUNFUTURE (CEX2019–000917-S), TED2021–130453B-C21, PID2020–112548RB-I00 and PID2019–107727RB-I00 projects, and from CSIC through the i-LINK (LINKA20338) program, is acknowledged. Project is also supported by a 2020 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation. TS and HT are financially supported by China Scholarship Council (CSC) with No. 201807000104 and 201906050014, respectively. TS and HT work has been done as a part of their Ph.D. program in Materials Science at Universitat Autònoma de Barcelona.The electron microscopy work has been carried out at the facilities of Centro Nacional de Microscopía Electrónica at UCM., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

Spin Hall magnetoresistance (SMR) is used to study interfacial magnetic features in La2CoMnO6 (LCMO)/Pt bilayers. LCMO is a ferromagnetic insulator with a Curie temperature Tc = 250 K and a strong magnetic anisotropy that can be tuned by microstructural strain. However, SMR measurements do not show any dependence on the strained state of the LCMO films. In addition, contrary to what may be expected, SMR signal persists above TC exhibiting a strong magnetic field dependence well above the saturation of the magnetization while the typical hysteresis on crossing H = 0 is absent. All these results suggest that the uppermost LCMO interfacial layers are magnetically uncoupled from the rest of the LCMO film and they do not show long range magnetic ordering. This fact is confirmed by a complete scanning transmission electron microscopy study of the interface that makes evident that the last atomic layers of the LCMO film do not contain Co and have a LaMnO3+δ simple perovskite-like structure with the last atomic layer being lanthanum oxide. The analysis of the experimental results according to recent SMR theories indicates, in fact, that the LCMO interfacial layer behaves as a 2D Heisenberg ferromagnet., The authors acknowledge financial support from the Spanish Ministry of Science and Innovation through Severo Ochoa (CEX2019-000917-S), Maria de Maeztu (CEX2020-001038-M), and SPINCURIOX (RTI2018-099960-BI00) and SCARFACE (RTI2018-094861-B-I00) projects co-financed by the European Regional Development Funds. The authors acknowledge the SEM-FIB microscopy service of the Universidad de Málaga and the ICTS-CNME for offering access to their instruments and expertise. S.M.-R. thanks the hospitality of CIC-nanoGUNE group. J.M.G.-P. and M.X.A.-P. thank the Spanish MICINN for a Ph.D. fellowship (Grant Nos. BES-2016-077301 and PRE-2019-089833, respectively). S.C. acknowledges support from the European Commission for a Marie Sklodowska-Curie Actions individual fellowship (Grant No. 796817-ARTEMIS)., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

Efficient spin injection from epitaxial ferrimagnetic ${\mathrm{Ni}\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ thin films into a $\mathrm{Pd}$ layer is demonstrated via spin Seebeck effect measurements in the longitudinal geometry. The ${\mathrm{Ni}\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ films (60 nm to 1 $\ensuremath{\mu}$) are grown by pulsed-laser deposition on isostructural spinel ${\mathrm{Mg}\mathrm{Al}}_{2}{\mathrm{O}}_{4}$, ${\mathrm{Mg}\mathrm{Ga}}_{2}{\mathrm{O}}_{4}$, and ${\mathrm{Co}\mathrm{Ga}}_{2}{\mathrm{O}}_{4}$ substrates with lattice mismatch varying between 3.2 and 0.2%. For the thinner films ($\ensuremath{\le}330$ nm), an increase in the spin Seebeck voltage is observed with decreasing lattice mismatch, which correlates well with a decrease in the Gilbert damping parameter as determined from ferromagnetic resonance measurements. High-resolution transmission electron microscopy studies indicate substantial decrease of antiphase boundary and interface defects that cause strain relaxation, i.e., misfit dislocations, in the films with decreasing lattice mismatch. This highlights the importance of reducing structural defects in spinel ferrites for efficient spin injection. It is further shown that angle-dependent spin Seebeck effect measurements provide a qualitative method to probe for in-plane magnetic anisotropies present in the films.

It is well known that in the high-temperature superconductor YBa2Cu3O7-x (YBCO), oxygen vacancies (VO) control the carrier concentration, its critical current density and transition temperature. In this work, it is revealed that VO also allows the accommodation of local strain fields caused by large-scale defects within the crystal. We show that the nanoscale strain associated with Y2Ba4Cu8O16 (Y124) intergrowths-that are common defects in YBCO-strongly affect the venue and concentration of VO. Local probe measurements in conjunction with density-functional-theory calculations indicate a strain-driven reordering of VO from the commonly observed CuO chains towards the bridging apical sites located in the BaO plane and bind directly to the superconducting CuO2 planes. Our findings have strong implications on the physical properties of the YBCO, as the presence of apical VO alters the transfer of carriers to the CuO2 planes, confirmed by changes in the Cu and O core-loss edge probed using electron energy loss spectroscopy, and creates structural changes that affect the Cu-O bonds in the superconducting planes. In addition, the revelation of apical VO also has implications on modulating critical current densities and enhancing vortex pinning.

Persistent photoconductance is a phenomenon found in many semiconductors, by which light induces long-lived excitations in electronic states. Commonly, persistent photoexcitation leads to an increase of carriers (accumulation), though occasionally it can be negative (depletion). Here, we present the quantum well at the LaAlO_{3}/SrTiO_{3} interface, where in addition to photoinduced accumulation, a secondary photoexcitation enables carrier depletion. The balance between both processes is wavelength dependent, and allows tunable accumulation or depletion in an asymmetric manner, depending on the relative arrival time of photons of different frequencies. We use Green's function formalism to describe this unconventional photoexcitation, which paves the way to an optical implementation of neurobiologically inspired spike-timing-dependent plasticity.

Ferroelectrics are characterized by domain structures as are other ferroics. At the nanoscale though, ferroelectrics may exhibit non-trivial or exotic polarization configurations under proper electrostatic and elastic conditions. These polar states may possess emerging properties not present in the bulk compounds and are promising for technological applications. Here, the observation of rotational polarization topologies at the nanoscale by means of aberration-corrected scanning transmission electron microscopy is reported in BaTiO

We use an original water-based chemical method to grow pure epitaxial BiFeO3 (BFO) ultra-thin films with excellent piezoelectric properties. Particularly, we show that this novel chemical route produces higher natural ferroelectric domain size distribution and coercive field compared to similar BFO films grown by physical methods. Moreover, we measured the d33 piezoelectric coefficient of 60 nm thick BFO films by a direct approach, using Direct Piezoelectric Force Microscopy (DPFM). As a result, first piezo-generated charge maps of a very thin BFO layer were obtained applying this novel technology. We also performed a comparative study of the d33 coefficients between standard PFM analysis and DPFM microscopy showing similar values i.e. 17 pm V-1 and 22 pC N-1, respectively. Finally, we proved that the directionality of the piezoelectric effect in BFO ferroelectric thin films is preserved at low thickness dimensions demonstrating the potential of chemical processes for the development of low cost functional ferroelectric and piezoelectric devices.

Materials that can couple electrical and mechanical properties constitute a key element of smart actuators, energy harvesters, or many sensing devices. Within this class, functional oxides display specific mesoscale responses which often result in great sensitivity to small external stimuli. Here, a novel combination of molecular beam epitaxy and a water-based chemical-solution method is used for the design of mechanically controlled multilevel device integrated on silicon. In particular, the possibility of adding extra functionalities to a ferroelectric oxide heterostructure by n-doping and nanostructuring a BaTiO

The chemical composition and the magnetic structure of individual La0.7Sr0.3MnO3 (LSMO) ferromagnetic manganite epitaxial nanostructures less than 200 nm in width are explored using Photoemission Electron Microscopy (PEEM). X-ray absorption spectra (XAS) provide separate information on the surface and the bulk composition of the nanoislands and give evidence of Mn(2+) present on the surface of otherwise stoichiometric nanostructures. Ferromagnetic domains less than 70 nm are resolved using X-ray magnetic circular dichroism (XMCD), which allows for the detection of magnetic vortex states in both (001)LSMO square and (111)LSMO triangular manganite nanoislands. The evolution of single nanostructures under an in-plane magnetic field is seen to depend on the specific nanoisland size and geometry. In particular, PEEM XMCD imaging allows detecting opposite chiralities as well as a variety of magnetization behaviors for different nanoislands.