Erratum: “Seed layer technique for high quality epitaxial manganite films” [AIP Advances 6, 085109 (2016)]

No abstract available

In-Depth NMR Investigation of the Magnetic Hardening in Co Thin Films Induced by the Interface with Molecular Layers

The hybridization of the surface orbitals of thin ferromagnetic layers with molecular orbitals represents a soft but efficient technology that is able to induce in ferromagnetic component radical modifications of the key magnetic parameters, such as magnetization, magnetic anisotropy, and others. These effects are investigated in 7 nm thick polycrystalline Co films interfaced with C-60 and Gaq(3) molecular layers by combining Co-59 Ferromagnetic nuclear resonance spectroscopy (FNR) and magneto-optic kerr effect (MOKE) techniques. It is demonstrated that the surface hybridization produces a significant magnetic hardening with respect to a reference Co/Al system and that the molecule-induced effects modify the magnetic properties of entire Co layer, propagating for several nm from the interface. The FNR spectroscopy also reveals a reconstruction of the magnetic environment at the cobalt surface, whose observation in polycrystalline films is especially intriguing. The results shed new and unexpected light on the interfacial physics in such systems, whose understanding necessitates further experimental and theoretical research

Surface nanostructures in manganite films

Ultrathin manganite films are widely used as active electrodes in organic spintronic devices. In this study, a scanning tunnelling microscopy (STM) investigation with atomic resolution revealed previously unknown surface features consisting of small non-stoichiometric islands. Based upon this evidence, a new mechanism for the growth of these complex materials is proposed. It is suggested that the non-stoichiometric islands result from nucleation centres that are below the critical threshold size required for stoichiometric crystalline growth. These islands represent a kinetic intermediate of single-layer growth regardless of the film thickness, and should be considered and possibly controlled in manganite thin-film applications

Energy level alignment at Alq3/La0.7Sr0.3MnO3 interface for organic spintronic devices

The electronic structure of the interface between Tris (8-hydroxyquinolino)-aluminum (Alq3) and La0.7Sr0.3MnO3 manganite (LSMO) was investigated by means of photoelectron spectroscopy. As demonstrated recently this interface is characterized by efficient spin injection in organic spintronic devices. We detected a strong interface dipole of about 0.9 eV that shifts down the whole energy diagram of the Alq3 with respect to the vacuum level. This modifies the height of the barriers for the holes injection to 1.7 eV, indicating that hole injection from LSMO into Alq3 is more difficult than it was expected as the energy level matched by vacuum levels. We believe the interface dipole is due to the intrinsic dipole moment characteristic for Alq3 layer. An additional weak interaction is observed between the two materials influencing the N 1s core levels of the organic semiconductor. The presented data are of greatest importance for both qualitative and quantitative description of the organic spin valves.Comment: 17 pages, 4 figure

Pentacene thin films on ferromagnetic oxide: Growth mechanism and spintronic devices

[EN] Cation-exchange membranes made exclusively from ceramic materials have been synthesized by means of the impregnation of microporous ceramic supports with zirconium phosphate. Changes in the pore size distribution and total pore volume of the supports were provoked by the addition of starch as pore former in the fabrication procedure. This allowed the production of supports with increased effective electrical conductivities and with larger pores available for the zirconium phosphate deposition. An improved functionality for the exchange of cations was given to the ceramic membranes by means of their impregnation with the active particles of zirconium phosphate. The ion-exchange properties of the membranes were increased with further impregnation cycles and the resulting current–voltage curves showed a similar shape to that typical of commercial polymeric ion-exchange membranes. The production of ionexchange membranes with increased chemical and radiation stability will broaden their applicability for the treatment of specific industrial waste waters, which are very aggressive for the current commercial ion-exchange membranes.The authors acknowledge the technical help from Federico Bona at CNR-ISMN in Bologna and the extensive use of the scanning probe microscopes at "Centro Interfacolta Misure" of the University of Parma. Financial support from the FP7 Projects NMP-2010-SMALL-4-263104 (HINTS), NMP3-SL-2010-246073 (GRENADA), and NMP3-LA-2010-246102 (IFOX) is acknowledged.Graziosi, P.; Riminucci, A.; Prezioso, M.; Newby, C.; Brunel, D.; Bergenti, I.; Pullini, D.... (2014). Pentacene thin films on ferromagnetic oxide: Growth mechanism and spintronic devices. Applied Physics Letters. 105(2):1-5. https://doi.org/10.1063/1.4890328S15105

Multi-modal sensing in spin crossover compounds

We exploited the solvatochromic spin-state switching in a spin crossover (SCO) compound based on the Fe-II complex and the simultaneous change of spectroscopic properties for selective multimodal sensing of methanol and ethanol. We demonstrate that sensing capabilities are due to the inclusion of methanol or ethanol molecules into the crystalline structure, which tailors simultaneously the transition temperature, colour, birefringence and vibrational modes. We exploited this capability by integrating a neutral compound, switchable at room temperature, into a micrometric TAG sensitive to the colour and birefringence. The system was characterised by optical microscopy, magnetic susceptibility, Raman spectroscopy and X-ray diffraction

Polaron framework to account for transport properties in metallic epitaxial manganite films

[EN] We propose a model for the consistent interpretation of the transport behavior of manganese perovskites in both the metallic and insulating regimes. The concept of polarons as charge carriers in the metallic ferromagnetic phase of manganites also solves the conflict between transport models, which usually neglects polaron effects in the metallic phase, and, on the other hand, optical conductivity, angle-resolved spectroscopy, and neutron scattering measurements, which identify polarons in the metallic phase of manganites down to 6 K. Transport characterizations of epitaxial La0.7Sr0.3MnO3 thin films in the thickness range of 5-40 nm and temperature interval of 25-410 K have been accurately collected. We show that taking into account polaron effects allows us to achieve an excellent fit of the transport curves in the whole temperature range. The current carriers density collapse picture accurately accounts for the properties variation across the metal-insulator transitions. The electron-phonon coupling parameter gamma estimations are in a good agreement with theoretical predictions. The results promote a clear and straightforward quantitative description of the manganite films involved in charge transport device applications and promises to describe other oxide systems involving a metal-insulator transition.The authors P.G., A.G., M.P., A.R., and I.B. thank F. Bona for technical help and A. Dediu and V. Kabanov for fruitful discussions. Financial support from the FP7 Projects No. NMP3-LA-2010-246102 (Interfacing oxides, IFOX), No. NMP-2010-SMALL-4-263104 (Next generation hybrid interfaces for spintronic applications, HINTS), No. NMP3-SL-2010-246073 (Graphene for nanoscaled applications, GRENADA), and the Italian government FIRB (Molecular nanomagnets on metallic and magnetic surfaces for applications in molecular spintronics) Project No. RBAP117RWN is acknowledged.Graziosi, P.; Gambardella, A.; Prezioso, M.; Riminucci, A.; Bergenti, I.; Homonnay, N.; Schmidt, G.... (2014). Polaron framework to account for transport properties in metallic epitaxial manganite films. Physical Review B. 89(21):1-7. https://doi.org/10.1103/PhysRevB.89.214411S17892

Surface induces different crystal structures in a room temperature switchable spin crossover compound

We investigated the influence of surfaces in the formation of different crystal structures of a spin crossover compound, namely [Fe(L)2] (LH: (2-(pyrazol-1-yl)-6-(1H-tetrazol-5-yl)pyridine), which is a neutral com- pound thermally switchable around room temperature. We observed that the surface induces the for- mation of two different crystal structures, which exhibit opposite spin transitions, i.e. on heating them up to the transition temperature, one polymorph switches from high spin to low spin and the second poly- morph switches irreversibly from low spin to high spin. We attributed this inversion to the presence of water molecules H-bonded to the complex tetrazolyl moieties in the crystals. Thin deposits were investi- gated by means of polarized optical microscopy, atomic force microscopy, X-ray diffraction, X-ray absorption spectroscopy and micro Raman spectroscopy; moreover the analysis of the Raman spectra and the interpretation of spin inversion were supported by DFT calculations