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Perpendicular shape anisotropy (PSA) and double magnetic tunnel junctions (DMTJ) offer practical solutions to downscale spin-transfer-torque Magnetic Random-Access Memory (STT-MRAM) beyond 20 nm technology nodes, whilst retaining their thermal stability and reducing critical currents applied. However, as these modern devices become smaller and three-dimensionally (3D) complex, our understanding of their functional magnetic behavior is often indirect, relying on magnetoresistance measurements and micromagnetic modelling. In this paper, we review recent work that was performed on these structures using a range of advanced electron microscopy techniques, focusing on aspects specific to the 3D and nanoscale nature of such elements. We present the methodology for the systematic transfer of individual SST-MRAM nano-pillars from large-scale arrays to image their magnetic configurations directly using off-axis electron holography. We show that improved phase sensitivity through stacking of electron holograms can be used to image subtle variations in DMTJs and the thermal stability of < 20 nm PSA-STT-MRAM nano-pillars during in-situ heating. The experimental practicalities, benefits and limits of using electron holography for analysis of MRAM devices are discussed, unlocking practical pathways for direct imaging of the functional magnetic performance of these systems with high spatial resolution and sensitivity., 22 pages, 7 figures

State-of-the-art halide perovskite solar cells employ semiconductor oxides as electron transport materials. Defects in these oxides, such as oxygen vacancies (Ovac), act as recombination centres and, in air and UV light, reduce the stability of the solar cell. Under the same conditions, the PbZrTiO3 ferroelectric oxide employs Ovac for the creation of defect-dipoles responsible for photo-carrier separation and current transport, evading device degradation. We report the application of PbZrTiO3 as the electron extraction material in triple cation halide perovskite solar cells. The application of a bias voltage (poling) up to 2 V, under UV light, is a critical step to induce charge transport in the ferroelectric oxide. Champion cells result in power conversion efficiencies of ∼11% after poling. Stability analysis, carried out at 1-sun AM 1.5 G, including UV light in air for unencapsulated devices, shows negligible degradation for hours. Our experiments indicate the effect of ferroelectricity, however alternative conducting mechanisms affected by the accumulation of charges or the migration of ions (or the combination of them) cannot be ruled out. Our results demonstrate, for the first time, the application of a ferroelectric oxide as an electron extraction material in efficient and stable PSCs. These findings are also a step forward in the development of next generation ferroelectric oxide-based electronic and optoelectronic devices., M. G. and S. M. Z. thank the European Union's Horizon 2020 programme, through a FET Open research and innovation action under grant agreement No. 687008 and the King Abdulaziz City for Science and Technology (KACST) for the financial support. H.-S. K. is grateful for the postdoctoral fellowship grant (NRF-2016R1A6A3A03012393). M. S. acknowledges support from the co-funded Marie Skłodowska Curie fellowship, H2020 grant agreement no. 665667. To the Spanish MINECO through the Severo Ochoa Centers of Excellence Program under Grant SEV-2013-0295 and for the postdoctoral contract for H. X.; for the grant ENE2016-79282-C5-2-R and the OrgEnergy Excelence Network CTQ2016-81911-REDT. To the Agència de Gestió d'Ajuts Universitaris i de Recerca for the support to the consolidated Catalonia research group 2017 SGR-329 and the Xarxa de Referència en Materials Avançats per a l'Energia (Xarmae). To the Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) for the contract ENE2015-74275-JIN to A. P. To the CERCA Programme/Generalitat de Catalunya and to the European COST Action StableNextSol project MP1307.

We report on the temperature and electric field driven evolution of the magnetoresistance lineshape at an interface between Ni/AlOx and Nb-doped SrTiO3. This is manifested as a superposition of the Lorentzian lineshape due to spin accumulation and a parabolic background related to tunneling anisotropic magnetoresistance (TAMR). The characteristic Lorentzian line shape of the spin voltage is retrieved only at low temperatures and large positive applied bias. This is caused by the reduction of the electric field at large positive applied bias which results in a simultaneous reduction of the background TAMR and a sharp enhancement in spin injection. Such mechanisms to tune magnetoresistance are uncommon in conventional semiconductors. Published by AIP Publishing.

We have designed, fabricated, and tested superconductor-insulator-superconductor (SIS) mixers based on Nb/AlN/NbN twin tunnel junctions for waveguide receivers operating in a frequency range of 790-950 GHz. Electromagnetic simulations and measurement results of the mixer performance are presented. The junctions have a high gap voltage of 3.15 mV and a high current density of about 30 kA/cm 2 , providing a wide receiver band, which was confirmed by Fourier transform spectrometer (FTS) and noise temperature measurements. The corrected receiver noise temperature varies from 240 K at low frequencies to 550 K at the high end of the band. The influence of the SIS junction heating on its characteristics has been studied and compared to another similar high current density technologies. The heating does not have a critical impact on the mixer performance.

We report polycrystalline BaTiO3 with cooperative magnetization behavior associated with the scarce presence of about 113 atomic ppm of Fe ions, clearly displaying magnetoelectric coupling with significant changes in magnetization (up to Delta M/M approximate to 32%) at the ferroelectric transitions. We find that Fe ions are segregated mostly at the interfaces between grain boundaries and an Fe-rich phase, forming a self-composite with high magnetoelectric coupling above room temperature. We compare our results with ab initio calculations and other experimental results found in the literature, proposing mechanisms that could be behind the magnetoelectric coupling within the ferroelectric matrix. These findings open the way for further strategies to optimize interfacial magnetoelectric couplings.

We investigate the coherent energy and thermal transport in a temperature-biased long Josephson tunnel junction, when a Josephson vortex, i.e., a soliton, steadily drifts driven by an electric bias current. We demonstrate that thermal transport through the junction can be controlled by the bias current, since it determines the steady-state velocity of the drifting soliton. We study the effects on thermal transport of the damping affecting the soliton dynamics. In fact, a soliton locally influences the power flowing through the junction and can cause the variation of the temperature of the device. When the soliton speed increases approaching its limiting value, i.e., the Swihart velocity, we demonstrate that the soliton-induces thermal effects significantly modify. Finally, we discuss how the appropriate material selection of the superconductors forming the junction is essential, since short quasiparticle relaxation times are required to observe fast thermal effects., Comment: 9 pages, 5 figures

Thanks to its excellent mechanical properties, graphene is particularly suited for the realization of suspended membranes. The present paper deals with one possible application of such membranes that is the realization of suspended lithographic masks for shadow evaporation onto a substrate. This technique, which is largely used for realizing mesoscopic devices, where the quality requirements for the junctions prevent the exposure to ambient air and the occurrence of quantum phenomena requires highly defined structures, can be improved by the use of pure 2-dimensional masks, like graphene ones. Advantages and differences of this material with respect to commonly employed polymers are presented and discussed.

Diodes incorporating a bilayer of an organic semiconductor and a wide bandgap metal oxide can show unipolar, non-volatile memory behavior after electroforming. The prolonged bias voltage stress induces defects in the metal oxide with an areal density exceeding 10(17) m(-2). We explain the electrical bistability by the coexistence of two thermodynamically stable phases at the interface between an organic semiconductor and metal oxide. One phase contains mainly ionized defects and has a low work function, while the other phase has mainly neutral defects and a high work function. In the diodes, domains of the phase with a low work function constitute current filaments. The phase composition and critical temperature are derived from a 2D Ising model as a function of chemical potential. The model predicts filamentary conduction exhibiting a negative differential resistance and nonvolatile memory behavior. The model is expected to be generally applicable to any bilayer system that shows unipolar resistive switching. (C) 2015 Author(s). Dutch Polymer Institute (DPI), BISTABLE [704]; Fundacao para Ciencia e Tecnologia (FCT) through the research Instituto de Telecommunicacoes (IT-Lx); project Memristor based Adaptive Neuronal Networks (MemBrAiNN) [PTDC/CTM-NAN/122868/2010]; European Community Seventh Framework Programme FP7', ONE-P [212311]; Dutch Ministry of Education, Culture and Science (Gravity Program) [024.001.035] info:eu-repo/semantics/publishedVersion

The magnetic and magnetotransport properties of Ni80Fe20/La0.7Sr0.3MnO3 (NiFe/LSMO) bilayers were investigated after bombarding the LSMO surface with low-energy Ar+ or O-2(+)/Ar+ ion beams before the growth of the top NiFe layer. A variety of magnetic properties are revealed, including an asymmetric two-stepped hysteresis loop with an exchange bias loop shift, and alternatively, a symmetric two-stepped hysteresis loop with an enhanced coercivity. Polarized neutron reflectometry measurements provide details of the magnetic depth profile and interface layer magnetism at different temperatures. The LSMO surface modifications determine a complex magnetic and electric NiFe/LSMO interface having a strong effect on the magnetoresistance of the bilayer. Surface engineering based on ion beam bombardment is presented as a promising technique for optimizing the electronic and magnetic properties of NiFe/LSMO junctions for future device applications. Published by AIP Publishing.

This work provides a detailed investigation of the measured in-plane field-swept homodyne-detected ferromagnetic resonance (FMR) spectra of an extended Co/Cu/NiFe pseudo spin valve stack using a nanocontact (NC) geometry. The magnetodynamics are generated by a pulse-modulated microwave current and the resulting rectified dc mixing voltage, which appears across the NC at resonance, is detected using a lock-in amplifier. Most notably, we find that the measured spectra of the NiFe layer are composite in nature and highly asymmetric, consistent with the broadband excitation of multiple modes. Additionally, the data must be fit with two Lorentzian functions in order to extract a reasonable value for the Gilbert damping of the NiFe. Aided by micromagnetic simulations, we conclude that (i) for in-plane fields the rf Oersted field in the vicinity of the NC plays the dominant role in generating the observed spectra, (ii) in addition to the FMR mode, exchange dominated spin waves are also generated, and (iii) the NC diameter sets the mean wavevector of the exchange dominated spin wave, in good agreement with the dispersion relation., 7 pages, 7 figures

We present a method that allows changing the anisotropy and the magnetic characteristics of piezoelectric–ferromagnetic hybrid structures by electric fields, thereby suppressing the need for external or local magnetic fields. We have investigated the magnetic properties of single Co50Fe50 and CoFe80B20 magnetostrictive thin films as well as of high-quality bottom-pinned spin valves (SV) sputtered on piezoelectric substrates [lead zirconate titanate (PZT)] and patterned in an interdigitated transducer (IDT). Induction of a uniaxial anisotropy axis and the changes on coercivity and switching fields as a function of the applied bias voltage on the IDT are analyzed and interpreted. The down-scalability of this hybrid method supports the possibility of achieving low-power/low-voltage control of the switching fields and shows the feasibility of a hybrid ferroelectric magnetic memory cell.

We have measured the absorption of terahertz radiation in a BCS superconductor over a broad range of frequencies from 200 GHz to 1.1 THz, using a broadband antenna-lens system and a tantalum microwave resonator. From low frequencies, the response of the resonator rises rapidly to a maximum at the gap edge of the superconductor. From there on the response drops to half the maximum response at twice the pair-breaking energy. At higher frequencies, the response rises again due to trapping of pair-breaking phonons in the superconductor. In practice this is the first measurement of the frequency dependence of the quasiparticle creation efficiency due to pair-breaking in a superconductor. The efficiency, calculated from the different non-equilibrium quasiparticle distribution functions at each frequency, is in agreement with the measurements.

We have measured the absorption of terahertz radiation in a BCS superconductor over a broad range of frequencies from 200 GHz to 1.1 THz, using a broadband antenna-lens system and a tantalum microwave resonator. From low frequencies, the response of the resonator rises rapidly to a maximum at the gap edge of the superconductor. From there on, the response drops to half the maximum response at twice the pair-breaking energy. At higher frequencies, the response rises again due to trapping of pair-breaking phonons in the superconductor. In practice, this is a measurement of the frequency dependence of the quasiparticle creation efficiency due to pair-breaking in a superconductor. The efficiency, calculated from the different non-equilibrium quasiparticle distribution functions at each frequency, is in agreement with the measurements.

We present a comparative study of high frequency dynamics and low frequency noise in elliptical magnetic tunnel junctions with lateral dimensions under 100 nm presenting current-switching phenomena. The analysis of the high frequency oscillation modes with respect to the current reveals the onset of a steady-state precession regime for negative bias currents above J = 10 7 A / cm 2, when the magnetic field is applied along the easy axis of magnetization. By the study of low frequency noise for the same samples, we demonstrate the direct link between changes in the oscillation modes with the applied current and the normalised low frequency (1/f) noise as a function of the bias current. These findings prove that low frequency noise studies could be a simple and powerful technique to investigate spin-torque based magnetization dynamics, We would like to acknowledge the support by the Spanish MINECO (MAT2012-32743), and the Comunidad de Madrid through NANOFRONTMAG-CM (S2013/MIT- 2850) and CCC-UAM (SVORTEX)

International audience; We study thin films and magnetic tunnel junction nanopillars based on Ta/Co20Fe60B20/MgO multilayers by electrical transport and magnetometry measurements. These measurements suggest that an ultrathin magnetic oxide layer forms at the Co20Fe60B20/MgO interface. At approximately 160 K, the oxide undergoes a phase transition from an insulating antiferromagnet at low temperatures to a conductive weak ferromagnet at high temperatures. This interfacial magnetic oxide is expected to have significant impact on the magnetic properties of CoFeB-based multilayers used in spin torque memories. (C) 2015 AIP Publishing LLC.

International audience; We report the observation of an atomic like behavior from T = 4.2 K up to room temperature in n- and p-type Omega-gate silicon nanowire (NW) transistors. For that purpose, we modified the design of a NW transistor and introduced long spacers between the source/drain and the channel in order to separate the channel from the electrodes. The channel was made extremely small (3.4 nm in diameter with 10 nm gate length) with a thick gate oxide (7 nm) in order to enhance the Coulomb repulsion between carriers, which can be as large as 200 meV when surface roughness promotes charge confinement. Parasitic stochastic Coulomb blockade effect can be eliminated in our devices by choosing proper control voltages. Moreover, the quantum dot can be tuned so that the resonant current at T = 4.2 K exceeds that at room temperature.

International audience; This paper investigates the effect of a controlled cooling rate on magnetic field reversal assisted by spin transfer torque (STT) in thermally assisted magnetic random access memory. By using a gradual linear decrease of the voltage at the end of the write pulse, the STT decays more slowly or at least at the same rate as the temperature. This condition is necessary to make sure that the storage layer magnetization remains in the desired written direction during cooling of the cell. The influence of the write current pulse decay rate was investigated on two exchange biased synthetic ferrimagnet (SyF) electrodes. For a NiFe based electrode, a significant improvement in writing reproducibility was observed using a gradual linear voltage transition. The write error rate decreases by a factor of 10 when increasing the write pulse fall-time from similar to 3 ns to 70 ns. For comparison, a second CoFe/NiFe based electrode was also reversed by magnetic field assisted by STT. In this case, no difference between sharp and linear write pulse fall shape was observed. We attribute this observation to the higher thermal stability of the CoFe/NiFe electrode during cooling. In real-time measurements of the magnetization reversal, it was found that Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling in the SyF electrode vanishes for the highest pulse voltages that were used due to the high temperature reached during write. As a result, during the cooling phase, the final state is reached through a spin-flop transition of the SyF storage layer. (C) 2015 AIP Publishing LLC.

We investigate ferroelectric resistive switching in BiFeO3 thin films by performing local conductivity measurements. By comparing conduction characteristics at artificially up-polarized domains with those at as-grown down-polarized domains, the change in resistance is attributed to the modification of the electronic barrier height at the interface with the electrodes, upon the reversal of the electrical polarization. We also study the effect of oxygen vacancies on the observed conduction and we propose the existence of a different screening mechanism for up and down polarized domains. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Identifying materials and devices which offer efficient thermoelectric effects at low temperature is a major obstacle for the development of thermal management strategies for low-temperature electronic systems. Superconductors cannot offer a solution since their near perfect electron-hole symmetry leads to a negligible thermoelectric response; however, here we demonstrate theoretically a superconducting thermoelectric transistor which offers unparalleled figures of merit of up to ∼45 and Seebeck coefficients as large as a few mV/K at sub-Kelvin temperatures. The device is also phase-tunable meaning its thermoelectric response for power generation can be precisely controlled with a small magnetic field. Our concept is based on a superconductor-normal metal-superconductor interferometer in which the normal metal weak-link is tunnel coupled to a ferromagnetic insulator and a Zeeman split superconductor. Upon application of an external magnetic flux, the interferometer enables phase-coherent manipulation of thermoelectric properties whilst offering efficiencies which approach the Carnot limit., The work of F.G. has been partially funded by the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC grant Agreement No. 615187-COMANCHE, and by the Marie Curie Initial Training Action (ITN) Q-NET 264034. J.W.A.R. acknowledges funding from the Royal Society (“Superconducting Spintronics”). J.W.A.R. and F.S.B. jointly acknowledge funding from the Leverhulme Trust through an International Network Grant (Grant No. IN-2013-033). J.S.M acknowledges funding from the National Science Foundation (Grant No. DMR 1207469) and the Office of Naval Research (Grant No. N00014-13-1-0301). The work of F.S.B. has been supported by the Spanish Ministry of Economy and Competitiveness under Project No. FIS2011-28851-C02-02.

The efficiency of the future devices for quantum information processing will be limited mostly by the finite decoherence rates of the individual qubits and quantum gates. Recently, substantial progress was achieved in enhancing the time within which a solid-state qubit demonstrates coherent dynamics. This progress is based mostly on a successful isolation of the qubits from external decoherence sources obtained by clever engineering. Under these conditions, the material-inherent sources of noise start to play a crucial role. In most cases, quantum devices are affected by noise decreasing with frequency, f, approximately as 1/f. According to the present point of view, such noise is due to material- and device-specific microscopic degrees of freedom interacting with quantum variables of the nanodevice. The simplest picture is that the environment that destroys the phase coherence of the device can be thought of as a system of two-state fluctuators, which experience random hops between their states. If the hopping times are distributed in a exponentially broad domain, the resulting fluctuations have a spectrum close to 1/f in a large frequency range. In this paper we review the current state of the theory of decoherence due to degrees of freedom producing 1/f noise. We discuss basic mechanisms of such noises in various nanodevices and then review several models describing the interaction of the noise sources with quantum devices. The main focus of the review is to analyze how the 1/f noise destroys their coherent operation. We start from individual qubits concentrating mostly on the devices based on superconductor circuits, and then discuss some special issues related to more complicated architectures. Finally, we consider several strategies for minimizing the noise-induced decoherence., Comment: Revised manuscript accepted for publication in Rev. Mod. Phys. 63 pages, 44 figures

Electrical contacts between nano-engineered systems are expected to constitute the basic building blocks of future nano-scale electronics. However, the accurate characterization and understanding of electrical contacts at the nano-scale is an experimentally challenging task. Here we employ low-temperature scanning tunneling spectroscopy to investigate the conductance of individual nano-contacts formed between flat Pb islands and their supporting substrates. We observe a suppression of the differential tunnel conductance at small bias voltages due to dynamical Coulomb blockade effects. The differential conductance spectra allow us to determine the capacitances and resistances of the electrical contacts which depend systematically on the island--substrate contact area. Calculations based on the theory of environmentally assisted tunneling agree well with the measurements., 5 pages, 3 figures, to appear in PRL

The fundamental noise limit of a phase-preserving amplifier at frequency $\omega /2\pi $ is the standard quantum limit $T_{q}=\hbar \omega /2k_{B}$. In the microwave range, the best candidates have been amplifiers based on superconducting quantum interference devices (reaching the noise temperature $T_{n} \sim 1.8 T_{q}$ at 700 MHz), and non-degenerate parametric amplifiers (reaching noise levels close to the quantum limit $T_{n}\approx T_{q}$ at 8 GHz). We introduce a new type of an amplifier based on the negative resistance of a selectively damped Josephson junction. Noise performance of our amplifier is limited by mixing of quantum noise from Josephson oscillation regime down to the signal frequency. Measurements yield nearly quantum-limited operation, $T_{n}=(3.2\pm 1.0) T_{q}$ at 2.8 GHz, owing to self-organization of the working point. Simulations describe the characteristics of our device well and indicate potential for wide bandwidth operation., Comment: 15 pages, 6 figures, supplementary information found in the published version

We report on the occurrence of multiple hopping and retrapping of a Brownian particle in a tilted washboard potential. The escape dynamic has been studied experimentally by measuring the switching current distributions as a function of temperature in a moderately damped NbN/MgO/NbN Josephson junction. At low temperatures the second moment of the distribution increases in agreement with calculations based on Kramers thermal activation regime. After a turn-over temperature T*, the shape of the distributions starts changing and width decreases with temperature. We analyze the data through fit of the switching probability and Monte Carlo simulations and we find a good agreement with a model based on a multiple retrapping process.

The stability of bunched fluxon states in inductively coupled Josephson junctions is analyzed for fluxons of both equal and opposite polarity. We demonstrate that unipolar fluxons may form stable bunched states if the velocity is above a given threshold. The stability of these bunched states is based on the existence of two characteristic velocities in the coupled system. The result of analytical stability analysis is in excellent agreement with the results of numerical simulations.

We have made a detailed study of the gain and noise of a SIS heterodyne receiver at 345 GHz. As mixing element we use an array of two Nb-Al2O3-Nb SIS junctions in series. The array is operated in a waveguide mount with a backshort and an E-plane tuner. The best receiver noise temperature achieved is 140 K DSB. The embedding impedances were determined by fitting theory to the measured pumped curves. High-quality fits are obtained which constitute the first detailed test of the Tucker-theory at frequencies above 300 GHz. The impedances found by this method are in very good agreement with impedances measured in a scale model at 3.3 GHz. From these embedding impedances gain and noise of the mixer were calculated over a full bias range using the Tucker theory in the three-port low IF approximation. The calculated values are compared to mixer gain and noise as obtained from receiver measurements. The observed dependence of mixer gain and noise on bias voltage, pump power and embedding impedance is in good agreement with theory. However the absolute value of the measured gain is a factor .45 +/- 0.05 lower than calculated. The measured mixer noise is approximately two quanta, 38 +/- 10 K, higher than calculated. These discrepancies appear to be independent of the bias parameters of the mixer.

The resonances of integrated tuning stubs in combination with SIS (superconductor-insulator-superconductor) detectors are measured and calculated. The predicted resonances are compared with measurements of stubs integrated with Nb-Al/sub 2/O/sub 3/-Nb junctions in a log-periodic antenna. Stubs of different lengths have been investigated on different substrates (on 200-mm thick quartz and on a 7-mm thick silicon membrane) and the results show a fairly good agreement with the model calculations. Quartz substrates showed resonances up to 640 GHz, while for silicon membranes stub resonances reach up to as 480 GHz. An observed resonance at 560 GHz is probably a substrate effect from the membrane. The gap frequency for all the samples is 670 GHz and no resonances are detected above this frequency. Up to the maximum detected frequency dispersion is found to be negligible. >

We demonstrate high temperature electrical spin injection and detection in degenerately p-doped GaAs in vertical spin valves using valence band electron tunneling. The maximum measured magnetoresistance at 10 and 300 K is 40% and similar to 1%, respectively. Spin relaxation in these devices was found to be relatively insensitive to temperature (T) for T> 125 K. The spin injection and detection efficiencies are mostly dominated by the ferromagnetic contact polarization and spin independent transport at the ferromagnet/semiconductor interface. (C) 2010 [doi:10.1063/1.3524820]

A superconducting double spin valve device is proposed. Its operation takes advantage of the interplay between the spin-filtering effect of ferromagnetic insulators and superconductivity-induced out-of-equilibrium transport. Depending on the degree of nonequilibrium, extraordinary large tunnel magnetoresistance as large as 10^2...10^6% can be obtained for realistic material parameters, and it can be tuned over several orders of magnitude under proper voltage biasing and temperature. The relevance of this setup for low-temperature applications is further discussed., 3+ pages, 3 color figures

X-ray spectroscopy measurements have been performed on a series of Pt/Co/AlOx trilayers to investigate the role of Co oxidation in the perpendicular magnetic anisotropy of the Co/AlOx interface. It is observed that high temperature annealing modifies the magnetic properties of the Co layer, inducing an enhancement of the perpendicular magnetic anisotropy. The microscopic structural properties are analyzed via X-ray Absorption Spectroscopy, X-ray Magnetic Circular Dichroism and X-ray Photoelectron Spectroscopy measurements. It is shown that annealing enhances the amount of interfacial oxide, which may be at the origin of a strong perpendicular magnetic anisotropy. (C) 2008 Elsevier B. V. All rights reserved.

The Fe3Si thin film is a good candidate as ferromagnetic electrode in spintronics devices due to its high spin polarization and high Curie temperature. The use of Fe3Si in contact with a thin SiO2 barrier can have various applications in practical devices, such as magnetic tunnel junctions. We report on the synthesis of Fe3Si/SiO2 structures, in one vacuum cycle, by pulsed laser deposition and glow-discharge plasma oxidation followed by vacuum annealing. The structural and morphological characterization of the Fe3Si/SiO2 stacks is performed by in-situ X-ray photoelectron spectroscopy and with atomic force microscopy. Using a Fe-57 tracer layer, conversion electron Mossbauer spectroscopy is performed at the Fe3Si/SiO2 interface, proving the formation of a ferromagnetic phase with no paramagnetic inclusions. Our experimental results indicate that the Fe3Si/SiO2 stack is a promising system for application in spintronics devices. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The adsorption of Fe on the SrTiO(3)(100) surface at room temperature has been studied in ultrahigh vacuum by means of Auger electron spectroscopy, low energy electron diffraction, electron energy loss spectroscopy, thermal desorption spectroscopy and work function measurements. The results show that iron probably grows in the mode of successive incomplete layers. For coverages >= 1.5 ML, a short range 1 x 1 order appears and the deposited Fe overlayer develops in body-centred cubic structure with Fe(100) parallel to SrTiO(3)(100) and crystallographic orientation Fe[110] parallel to SrTiO(3)[100]. The results of the electron spectroscopies do not indicate any iron oxidation at the metal-oxide interface. Instead, an interaction between the Fe adatoms gradually leads to the metallization of the Fe overlayer. Thus, the Fe/SrTiO(3)(100) interface seems to be a rather abrupt metal-oxide interface, which presents a good thermal stability for annealing up to similar to 800 K. In conclusion, this adsorption system looks ideal for free-standing ultrathin Fe films and low-dimensional structures, useful for technological applications. Journal of Physics-Condensed Matter

We study spin-polarized transient transport in a quantum dot coupled to two ferromagnetic leads subjected to a rectangular bias voltage pulse. Time-dependent spin-resolved currents, occupations, spin accumulation, and tunneling magnetoresistance (TMR) are calculated using both nonequilibrium Green function and master equation techniques. Both parallel and antiparallel leads' magnetization alignments are analyzed. Our main findings are: a dynamical spin accumulation that changes sign in time, a short-lived pulse of spin polarized current in the emitter lead (but not in the collector lead), and a dynamical TMR that develops negative values in the transient regime. We also observe that the intra-dot Coulomb interaction can enhance even further the negative values of the TMR., 7 pages, 6 figures. Typos corrections corresponding to the published version

Several aspects of half-metallic magnetism at finite temperature are discussed. Since NiMnSb is the simplest half-metal and the longest known it will be used as an example. Also it is a half-metal with remarkable little on-site Coulomb repulsion. Consequently it is a half-metal that is not notably corrupted by non-quasiparticle states. There exists an anomaly at 90 K, described before, that will be shown to be unrelated to the position of the Fermi level in the bandgap. Several substitutions are investigated that could shed some light on the origin of the transition. The calculated phonon spectrum is compared with experimental neutron scattering data. Finally, the spin-polarization of interfaces of NiMnSb with the transition metal based non-magnetic semiconductors NiTiSn and CoTiSb is investigated and the electronic structure of an infinite two-dimensional array of NiMnSb quantum dots embedded in NiScSb is reported.

We present experiments on a superconductor-normal metal electron refrigerator in a regime where single-electron charging effects are significant. The system functions as a heat transistor, i.e., the heat flux out from the normal metal island can be controlled with a gate voltage. A theoretical model developed within the framework of single-electron tunneling provides a full quantitative agreement with the experiment. This work serves as the first experimental observation of Coulombic control of heat transfer and, in particular, of refrigeration in a mesoscopic system., Comment: 4 pages, 3 color figures

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