Thickness dependent magnetic anisotropy of ultrathin LCMO epitaxial thin films

The magnetic properties of La0.7Ca0.3MnO3 (LCMO) manganite thin films were studied with magnetometry and ferromagnetic resonance as a function of film thickness. They maintain the colossal magnetoresistance behavior with a pronounced metal-insulator transition around 150-200 K, except for the very thinnest films studied (3 nm). Nevertheless, LCMO films as thin as 3 nm remain ferromagnetic, without a decrease in saturation magnetization, indicating an absence of dead-layers, although below approx. 6 nm the films remain insulating at low temperature. Magnetization hysteresis loops reveal that the magnetic easy axes lie in the plane of the film for thicknesses in the range of 4-15 nm. Ferromagnetic resonance studies confirm that the easy axes are in-plane, and find a biaxial symmetry in-plane with two, perpendicular easy axes. The directions of the easy axes with respect to the crystallographic directions of the cubic SrTiO3 substrate differ by 45 degrees in 4 nm and 15 nm thick LCMO films.Comment: Presented at Intermag conference (Madrid, 2008). Accepted for publication in IEEE Transactions on Magnetic

Growth and Electrostatic/chemical Properties of Metal/LaAlO₃/SrTiO₃ Heterostructures

International audienc

Competition between covalent bonding and charge transfer at complex-oxide interfaces

Here we study the electronic properties of cuprate/manganite interfaces. By means of atomic resolution electron microscopy and spectroscopy, we produce a subnanometer scale map of the transition metal oxidation state profile across the interface between the high $T_c$ superconductor YBa$_2$Cu$_3$O$_{7-\delta}$ and the colossal magnetoresistance compound (La,Ca)MnO$_3$. A net transfer of electrons from manganite to cuprate with a peculiar non-monotonic charge profile is observed. Model calculations rationalize the profile in terms of the competition between standard charge transfer tendencies (due to band mismatch), strong chemical bonding effects across the interface, and Cu substitution into the Mn lattice, with different characteristic length scales.Comment: 11+7 pages, 3+2 figure

Light induced decoupling of electronic and magnetic properties in manganites

The strongly correlated material La0.7Sr0.3MnO3 (LSMO) exhibits metal-to-insulator and magnetic transition near room temperature. Although the physical properties of LSMO can be manipulated by strain, chemical doping, temperature, or magnetic field, they often require large external stimuli. To include additional flexibility and tunability, we developed a hybrid optoelectronic heterostructure that uses photocarrier injection from cadmium sulfide (CdS) to an LSMO layer to change its electrical conductivity. LSMO exhibits no significant optical response, however, the CdS/LSMO heterostructures show an enhanced conductivity, with ~ 37 % resistance drop, at the transition temperature under light stimuli. This enhanced conductivity in response to light is comparable to the effect of a 9 T magnetic field in pure LSMO. Surprisingly, the optical and magnetic responses of CdS/LSMO heterostructures are decoupled and exhibit different effects when both stimuli are applied. This unexpected behavior shows that heterostructuring strongly correlated oxides may require a new understanding of the coupling of physical properties across the transitions and provide the means to implement new functionalities

Giant topological Hall effect in correlated oxide thin films

Strong electronic correlations can produce remarkable phenomena such as metal–insulator transitions and greatly enhance superconductivity, thermoelectricity or optical nonlinearity. In correlated systems, spatially varying charge textures also amplify magnetoelectric effects or electroresistance in mesostructures. However, how spatially varying spin textures may influence electron transport in the presence of correlations remains unclear. Here we demonstrate a very large topological Hall effect (THE) in thin films of a lightly electron-doped charge-transfer insulator, (Ca,Ce)MnO3. Magnetic force microscopy reveals the presence of magnetic bubbles, whose density as a function of magnetic field peaks near the THE maximum. The THE critically depends on carrier concentration and diverges at low doping, near the metal–insulator transition. We discuss the strong amplification of the THE by correlation effects and give perspectives for its non-volatile control by electric fields.The authors thank V. Cros, V. Dobrosavljevic, J. Iñiguez, J.-V. Kim, D. Maccariello, J. Matsuno, I. Mertig, N. Nagaosa and N. Reyren for useful discussions, J.-Y. Chauleau and M. Viret for second harmonic generation experiments, N. Jaouen for resonant magnetic X-ray diffraction, J. Varignon for preparing Fig. 1a and J.-M. George for his help with some magnetotransport measurements. This research received financial support from the ERC Consolidator grant ‘MINT’ (contract no. 615759) and ANR project ‘FERROMON’. This work was also supported by a public grant overseen by the ANR as part of the ‘Investissement d’Avenir’ programme (LABEX NanoSaclay, ref. ANR-10-LABX-0035) through projects ‘FERROMOTT’ and ‘AXION’ and by the Spanish Government through project no. MAT2014-56063-C2-1-R and MAT2017-85232-R (AEI/FEDER, UE), and Severo Ochoa SEV-2015-0496 and the Generalitat de Catalunya (2014SGR 734 project). B.C. acknowledges grant no. FPI BES-2012-059023, R.C. acknowledges support from CNPq-Brazil, and J.S. thanks the University Paris-Saclay (D’Alembert programme) and CNRS for financing his stay at CNRS/Thales. Work at Rutgers was supported by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, US Department of Energy under award no. DE-SC0018153. H.K. is supported by JSPS KAKENHI grants nos. 25400339, 15H05702 and 17H02929. K.N. is supported by a Grant-in-Aid for JSPS Research Fellow grant no. 16J05516, and by a Program for Leading Graduate Schools ‘Integrative Graduate Education and Research in Green Natural Sciences’.Peer reviewe

Encapsulation of MSCs and GDNF in an Injectable Nanoreinforced Supramolecular Hydrogel for Brain Tissue Engineering

The co-administration of glial cell line-derived neurotrophic factor (GDNF) and mesenchymal stem cells (MSCs) in hydrogels (HGs) has emerged as a powerful strategy to enhance the efficient integration of transplanted cells in Parkinson's disease (PD). This strategy could be improved by controlling the cellular microenvironment and biomolecule release and better mimicking the complex properties of the brain tissue. Here, we develop and characterize a drug delivery system for brain repair where MSCs and GDNF are included in a nanoparticle-modified supramolecular guest-host HA HG. In this system, the nanoparticles act as both carriers for the GDNF and active physical crosslinkers of the HG. The multifunctional HG is mechanically compatible with brain tissue and easily injectable. It also protects GDNF from degradation and achieves its controlled release over time. The cytocompatibility studies show that the developed biomaterial provides a friendly environment for MSCs and presents good compatibility with PC12 cells. Finally, using RNA-sequencing (RNA-seq), we investigated how the three-dimensional (3D) environment, provided by the nanostructured HG, impacted the encapsulated cells. The transcriptome analysis supports the beneficial effect of including MSCs in the nanoreinforced HG. An enhancement in the anti-inflammatory effect of MSCs was observed, as well as a differentiation of the MSCs toward a neuron-like cell type. In summary, the suitable strength, excellent self healing properties, good biocompatibility, and ability to boost MSC regenerative potential make this nanoreinforced HG a good candidate for drug and cell administration to the brain

Electrically Switchable and Tunable Rashba-Type Spin Splitting in Covalent Perovskite Oxides

International audienceIn transition metal perovskites (ABO3) most physical properties are tunable by structural parameters such as the rotation of the BO6 octahedra. Examples include the Néel temperature of orthoferrites, the conductivity of mixed-valence manganites, or the band gap of rare-earth scan-dates. Since oxides often host large internal electric dipoles and can accommodate heavy elements, they also emerge as prime candidates to display Rashba spin-orbit coupling, through which charge and spin currents may be efficiently interconverted. However, despite a few experimental reports in SrTiO3-based interface systems, the Rashba interaction has been little studied in these materials, and its interplay with structural distortions remain unknown. In this Letter, we identify a bismuth-based perovskite with a giant, electrically-switchable Rashba interaction whose amplitude can be controlled by both the ferroelectric polarization and the breathing mode of oxygen octahedra. This particular structural parameter arises from the strongly covalent nature of the Bi-O bonds, reminiscent of the situation in perovskite nickelates. Our results not only provide novel strategies to craft agile spin-charge converters but also highlight the relevance of covalence as a powerful handle to design emerging properties in complex oxides