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Novel applications for memory devices demand nanoscale flexible structures. In particular, resistive switching (RS) devices are promising candidates for wearable and implantable technologies. Here, the Pt/Si/Ag/TiW metal-insulator-metal structure was fabricated and characterized on top of flexible substrates using a straightforward microfabrication process. We also showed that these substrates are compatible with sputtering deposition. RS was successfully achieved using both commercial cellulose cleanroom paper and bacterial cellulose, and polymer (PET) substrates. The bipolar switching behavior was observed for both flat and bent (under a radius of 3.5 mm) configurations. The observed phenomenon was explained by the formation/rupture of metallic Ag filaments in the otherwise insulating Si host layer. FEDER (Fundo Europeu de Desenvolvimento Regional) funds through the COMPETE 2020 Operational Programme for Competitiveness and Internationalisation (POCI), Portugal 2020 FCT (Fundacao para a Ciencia e a Tecnologia)Portuguese Foundation for Science and Technology Ministerio da Ciencia, Tecnologia e Inovacao [POCI-010145 FEDER007274] Associated LaboratoryInstitute of Nanoscience and Nanotechnology FSE/POPHEuropean Social Fund (ESF) FCTPortuguese Foundation for Science and TechnologyEuropean Commission [SFRH/BD/101661/2014, CEECIND/00464/2017] FCT through the IN Associated Laboratory National Infrastructure Roadmap [NORTE-01-0145-FEDER-22090] [PTDC/CTM-NAN/122868/2010] [PTDC/CTM-NAN/3146/2014] [PTDC/NAN-MAT/31688/2017] [UID/CTM/50011/2019] [UID/EEA/50008/2019] [POCI-01-0145-FEDER-016623] info:eu-repo/semantics/publishedVersion

Magnetic fields generated by current lines are the standard way of switching between resistance (R) states in magnetic random access memories. A less common but technologically more interesting alternative to achieve R-switching is to use an electrical current crossing the tunnel barrier. Such current induced magnetization switching (CIMS) or current induced switching (CIS) effects were recently observed in thin magnetic tunnel junctions, and attributed to spin transfer (CIMS) or electromigration of atoms into the insulator (CIS). In this work, electromigration-driven resistance changes (resistive switching) are superimposed with thermally induced pinned layer reversal (magnetic switching), producing a reproducible, three-state memory device. The tunnel junctions under study show a tunnel magnetoresistance of 14% with a RA product of 50 �µ m 2 . The reversible electromigration-driven resistance changes amount to 7–8% of the full resistance change and more than 10 4 R-switching events can be current induced without significant damage to the tunnel junction. Typical critical current densities are of the order of 2 × 10 6 Ac m −2 .

The great advances in nanoscience and nanotechnology in the last decade have led to the development of new platforms where all physical properties such as size, porosity, geometry and surface can be controlled at the nanoscale. Self-organized nanostructuring using template synthesis is a very promising and rapidly expanding field for the preparation of many different ordered structures ranging from the micrometer to the nanometer size. Porousaluminium, titanium, iron or hafnium oxide templates demonstrated real potential as well-controlled self-organized nanostructured materials for various applications. They are also an elegant tool to fabricate two- or three-dimensional arrays of periodic nanostructures. This work presents detailed methods to implement and fabricate nanoporous templates by anodic oxidation of Al and Ti metal substrates (that can be further used for Fe or Hf anodization). The characterization of nanowires grown in the pores of the synthesized Al2O3 and TiO2 templates is also discussed.

The introduction of voids in a magnetic thin-film alters the stray field distribution and enables the tailoring of the corresponding physical properties. Here we present a detailed study on thin magnetic nanohole arrays (NhAs) grown on top of hexagonally-ordered anodic aluminum oxide (AAO) substrates. We address the effect of AAO topography on the corresponding electrical and magneto-transport properties. Optimization of the AAO topography led to NhAs with improved resistance and magnetoresistance responses, while retaining their most important feature of enhanced coercivity. This opens new pathways for the growth of more complex structures on AAO substrates, a crucial aspect for their technological viability. © 2012 IOP Publishing Ltd., DCL, CTS and JMT acknowledge FCT grants (SFRH/BPD/72359/2010, SFRH/BPD/82010/2011 and SFRH/BPD/72329/2010, respectively). JV acknowledges funding through FSE/POPH. Partial support was provided by the Spanish Ministry of Economia y Competitividad under project MAT2010-20798-C05-01.

Indium phosphide thin films were grown onto glass substrates by RF magnetron sputtering. In this paper, we present a study on the role of argon pressure and rf power on magnetron sputtered InP films. These sputtering parameters are shown to affect the deposition rate, structure, morphology, electrical and optical properties of InP films. Single-phase, nearly stoichiometric and polycrystalline films exhibiting zinc blende structure with strong preferred orientation along (111) were observed at an argon pressure of 0.4 Pa, by keeping the substrate temperature (448 K) and RF power (150 W) constant. Hall measurements indicated n-type conductivity in InP films. The optical absorption studies indicated a direct band gap of 1.35 eV.

Magnetic tunnel junctions (MTJs) are under investigation since they offer great potential for applications in magnetic memories. An interesting effect in TJs concerns non-volatile resistive switching of non-magnetic origin. We report magnetic (magnetoresistance) and structural (resistive; R) switching in MgO-based MTJs (barrier thicknesses t = 0.75, 1.35 nm). As-grown MTJs display R-switching only in the thinnest series, while thicker barrier samples need an electroforming step for R-switching to occur. Forming changes the electrical resistance temperature dependence, from tunnel- to metallic-like, revealing the formation of conductive bridges across the barrier which, leading to local high electrical fields and temperatures, are essential for resistive switching.

A simple tight-binding theoretical model is proposed for spin dependent, current-in-plane transport in highly coherent spin valve structures under specularity conditions. Using quantum-mechanically coherent and spatially quantized Fermi states in the considered multilayered system, a system of partial Boltzmann kinetic equations is built for relevant subbands to yield the expressions for conductance in parallel or antiparallel spin valve states and thus for the magneto-conductance. It is shown that specularity favors the magnetoresistance to reach its theoretical maximum for this structure close to 100%. This result is practically independent of the model parameters, in particular it does not even need that lifetimes of majority and minority carriers be different (as necessary for the quasiclassical regimes). The main MR effect in the considered limit is due to the transformation of coherent quantum states, induced by the relative rotation of magnetization in the FM layers. Numerical calculation based on the specific Boltzmann equation with an account of spin-dependent specular reflection at the interfaces is also performed for a typical choice of material parameters., Comment: 5 pages, 5 figures