Suchergebnisse

Valvidares, M. et al. ; Ultrathin Pt films grown on insulating ferrimagnetic CoFe2O4 (111) epitaxial films display a magnetoresistance upon rotating the magnetization of the magnetic layer. We report here x-ray magnetic circular dichroism (XMCD) recorded at Pt-L2,3 and Pt-M3 edges. The results indicate that the Pt magnetic moment, if any, is below the detection limit (<0.001μB/Pt), thus strongly favoring the view that the presence of CoFe2O4 does not induce the formation of magnetic moments in Pt. Therefore, the observed magnetoresistance cannot be attributed to some sort of proximity-induced magnetic moments at Pt ions and subsequent magnetic-field dependent scattering. It thus follows that either bulk (spin Hall and inverse spin Hall effects) or interface (Rashba) spin-orbit related effects dominate the observed magnetoresistance. Furthermore, comparison of bulk magnetization and XMCD data at (Fe,Co)-L2,3 edges suggests the presence of some spin disorder in the CoFe2O4 layer which may be relevant for the observed anomalous nonsaturating field dependence of spin Hall magnetoresistance. ; This work is supported by the European Union under the NMP project (263104-HINTS) and the European Research Council (257654-SPINTROS). The financial support from the Spanish Ministry of Economy and Competitiveness, through the "Severo Ochoa" Program for Centers of Excellence in R&D (SEV-2015-0496) and the projects (MAT2012-37638, MAT2014-56063-C2-1-R, FIS2013-45469-C4-3-R, MAT2014-59315-R and MAT2015-65159-R) and by the Catalan Government (2014 SGR 734) are acknowledged. M. I. acknowledges the Basque Government for a PhD fellowship (BFI-2011-106). Beam time access at ESRF and ALBA facilities, at beamlines ID12 and BL29 respectively, is also acknowledged. ; Peer reviewed

Ferroelectric HfO2 epitaxial films are of interest for determining intrinsic properties and for prototyping devices. Epitaxial (111)-oriented orthorhombic Hf0.5Zr0.5O2 films grown on La0.67Sr0.33MnO3/SrTiO3(001) are already being actively investigated. Now, we have explored the use of SrTiO3(111) substrates. We show that the orthorhombic phase is stabilized by tilted epitaxy, and the orientation of the orthorhombic crystallites is different from that of equivalent films on SrTiO3(001). The measured remanent polarization of above 14 µC cm-2 agrees well with the expected value considering the crystal orientation, the fraction of ferroelectric phase in the film, and the predicted polarization of ferroelectric HfO2. High endurance and retention are also measured. ; Financial support from the Spanish Ministry of Science and Innovation (MCIN/AEI/ 10.13039/501100011033), through the Severo Ochoa FUNFUTURE (CEX2019-000917-S), PID2020- 112548RB-I00 and PID2019-107727RB-I00 projects, from CSIC through the i-LINK (LINKA20338) program, and from Generalitat de Catalunya (2017 SGR 1377) is acknowledged. Project supported by a 2020 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation. IF acknowledges Ramón y Cajal contract RYC-2017-22531. TS is financially supported by China Scholarship Council (CSC) with No. 201807000104. TS work has been done as a part of his Ph.D. program in Materials Science at Universitat Autònoma de Barcelona. SE acknowledges the Spanish Ministry of Science and Innovation for his PhD contract (SEV-2015-0496-16-3) and its cofunding by the ESF. 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). ; Peer reviewed

López-Conesa, L. et al. ; LaNiO3 (LNO) thin films of 14 nm and 35 nm thicknesses grown epitaxially on LaAlO3 (LAO) and (LaAlO3)0.3(Sr2TaAlO6)0.7 (LSAT) substrates are studied by High Resolution Transmission Electron Microscopy (HRTEM) and (High Angle Annular Dark Field (HAADF) imaging. The strain state of the films is studied by Geometric Phase Analysis (GPA). Results show the successful in-plane adaptation of the films to the substrates, both in the compressive (LAO) and tensile (LSAT) cases. Through the systematic analysis of HRTEM superstructure contrast modulation along different crystal orientations, localized regions of the monoclinic LaNiO2.5 phase are detected in the 35 nm films. ; LLC, JMR, SE and FP acknowledge financial support by the Spanish Government (projects MAT2013-41506 and CSD2009-2013). ICMAB activity has been sponsored by the Spanish MINECO (Project:MAT2014-56063-C02) and the "Severo Ochoa" Programme for Centres of Excellence in R&D (SEV-2015-0496)), and by Generalitat de Catalunya (2014 SGR 00734). TEM facilities at CCiT-UB, CEMES-CNRS and LMA-INA are also acknowledged. ; Peer reviewed

Khestanova, Ekaterina et al. ; The polarization of ferroelectric superlattices is determined by both electrical boundary conditions at the ferroelectric/paraelectric interfaces and lattice strain. The combined infl uence of both factors offers new opportunities to tune ferroelectricity. However, the experimental investigation of their individual impact has been elusive because of their complex interplay. Here, a simple growth strategy has permitted to disentangle both contributions by an independent control of strain in symmetric superlattices. It is found that fully strained short-period superlattices display a large polarization whereas a pronounced reduction is observed for longer multilayer periods. This observation indicates that the electrostatic boundary mainly governs the ferroelectric properties of the multilayers whereas the effects of strain are relatively minor. ; Financial support by the Spanish Government [Projects MAT2014- 56063-C2-1-R and MAT2013-41506 ] and Generalitat de Catalunya ( 2014-SGR-734 and 2014-SGR-672 ) is acknowledged. ICMAB-CSIC authors acknowledge fi nancial support from the Spanish Ministry of Economy and Competitiveness , through the "Severo Ochoa" Programme for Centres of Excellence in R&D (SEV- 2015-0496 ). I.F. acknowledges Juan de la Cierva – Incorporación postdoctoral fellowship (IJCI-2014- 19102) from the Spanish Ministry of Economy and Competitiveness. The transmission electron microscopy works were conducted in the Laboratorio de Microscopias Avanzadas at Instituto de Nanociencia de Aragón (Universidad de Zaragoza). The authors acknowledge the LMA-INA for offering access to their instruments and expertise. The authors thank Massimiliano Stengel for useful discussions. ; Peer reviewed

We study the spin Hall magnetoresistance (SMR) in Pt grown in situ on CoFe2O4 (CFO) ferrimagnetic insulating films. A careful analysis of the angle-dependent and field-dependent longitudinal magnetoresistance indicates that the SMR contains a contribution that does not follow the bulk magnetization of CFO, but it is a fingerprint of the complex magnetism at the surface of the CFO layer, thus signaling SMR as a tool for mapping surface magnetization. A systematic study of the SMR for different temperatures and CFO thicknesses gives us information impossible to obtain with any standard magnetometry technique. On one hand, the surface magnetization behaves independently of the CFO thickness and does not saturate up to high fields, evidencing that the surface has its own anisotropy. On the other hand, characteristic zero-field magnetization steps are not present at the surface while they are relevant in the bulk, strongly suggesting that antiphase boundaries are responsible for such intriguing features. In addition, a contribution from the ordinary magnetoresistance of Pt is identified, which is distinguishable only due to the low resistivity of the in situ grown Pt. ; This work is supported by the European Union under the NMP project (263104-HINTS) and the European Research Council (257654-SPINTROS), by the Spanish MINECO (MAT2012-37638, MAT2015-65159-R, MAT2014-56063- C2-1R, and SEV-2015-0496), by the Basque Government (PC2015-1-01), and by the Catalan Government (2014 SGR 734). M. I. and E. S. acknowledge the Basque Government and the Spanish MECD, respectively, for a Ph.D. fellowship (BFI-2011-106 and FPU14/03102). J. F. acknowledges stimulating discussions with Xavier Martí. ; Peer reviewed

The multifunctional (ferromagnetic and ferroelectric) response at room temperature that is elusive in single phase multiferroic materials can be achieved in a proper combination of ferroelectric perovskites and ferrimagnetic spinel oxides in horizontal heterostructures. In this work, lead-free CoFe2O4/BaTiO3 bilayers are integrated with Si(001) using LaNiO3/CeO2/YSZ as a tri-layer buffer. They present structural and functional properties close to those achieved on perovskite substrates: the bilayers are fully epitaxial with extremely flat surface, and exhibit robust ferromagnetism and ferroelectricity at room temperature. ; Financial support by the Spanish Government (projects MAT2014-56063-C2-1-R and FIS2013-48668-C2-1-P) and Generalitat de Catalunya (2014 SGR 734) is acknowledged. ICMAB-CSIC authors 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). IF acknowledges Beatriu de Pinós postdoctoral scholarship (2011 BP-A 00220 and 2011 BP-A_2 00014) from AGAUR-Generalitat de Catalunya and Juan de la Cierva - Incorporación postdoctoral fellowship (IJCI-2014-19102) from the Spanish Ministry of Economy and Competitiveness. MS acknowledges the FPU grant and JG acknowledges RyC contract (2012–11709) from the Spanish Government. Electron microscopy observations carried out at the ICTS-CNME at UCM. Authors acknowledge the ICTS-CNME for offering access to their instruments and expertise. Research at UCM was sponsored by Spanish MINECO MAT2015-66888-C3-3-R and Fundación BBVA. ; Peer reviewed