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2D-materials-based biosensing, supported by artificial intelligence (AI) and internet-of-medical things (IoMT), has emerged as a new technological platform for intelligent diagnostics at point-of-care (POC). To achieve a desired biosensing, high performance engineering in smart functionalized opto-electric 2D materials is crucial. Recently, borophene has emerged as one of such advanced platforms due to its high electroactive surface, anisotropic behaviour, high electron transport, controlled optical properties, feasibility of deposition in thin films, and possibility to generate surface functionalities. Although ease of fabrication still stands challenging, borophene could be deposited on flexible substrate, functionalized using chemistries to immobilize bio-actives, and control over electro-optical properties to develop a highly sensitive biosensing systems operated by smartphone to achieve early stage POC diagnosis. This letter is an attempt to project borophene for smart bio-sensing.

Hall-effect in semiconductors has wide applications for magnetic field sensing. Yet, a standard Hall sensor retains two problems: its linearity is affected by the non-uniformity of the current distribution; the sensitivity is bias-dependent, with linearity decreasing with increasing bias current. In order to improve the performance, we here propose a novel structure which realizes bias-free, photo-induced Hall sensors. The system consists of a semi-transparent metal Pt and a semiconductor Si or GaAs to form a Schottky contact. We systematically compared the photo-induced Schottky behaviors and Hall effects without net current flowing, depending on various magnetic fields, light intensities and wavelengths of Pt/GaAs and Pt/Si junctions. The electrical characteristics of the Schottky photo-diodes were fitted to obtain the barrier height as a function of light intensity. We show that the open-circuit Hall voltage of Pt/GaAs junction is orders of magnitude lower than that of Pt/Si, and the barrier height of GaAs is smaller. It should be attributed to the surface states in GaAs which block the carrier drifting. This work not only realizes the physical investigations of photo-induced Hall effects in Pt/GaAs and Pt/Si Schottky junctions, but also opens a new pathway for bias-free magnetic sensing with high linearity and sensitivity comparing to commercial Hall-sensors.

The interfaces’ structure and chemical roughness play an important role on the magnetic properties of thin-film multilayer devices. Within the past two decades, there has been a surge of interest in the use of low-dose ion-beam irradiation to engineer topology of buried interfaces, without changing the morphology, and to control magnetic properties of multilayer heterostructures consequently. This interest has recently been stimulated by promising results in the emerging sub-field of spin-orbitronics. In this chapter, the possible applications of ion-beam irradiation towards the modification of different magnetic properties of thin-film heterostructures are explored.

Some low-temperature magnetic sensors are based on the Hall effect in thin metallic films. However, their sensitivity is more than one order of magnitude smaller than that of silicon-based Hall sensors operating at room temperature. Furthermore, in order to avoid significant Joule heating, only very small bias currents can be injected at low temperatures. Here, we show that a sensor based on a photoinduced Hall effect, in which charge is photogenerated in a semiconductor and injected into an adjacent metallic layer, can be used as a bias-free, cryogenic sensor. The system consists of a platinum thin film deposited on intrinsic-silicon substrate. The film forms a Schottky interface with the semiconductor. At room temperature, carriers photogenerated in the semiconductor are injected into the metal, because of rounding-off of the Schottky barrier, and are deflected by a magnetic field applied in the film plane. At cryogenic temperatures, and well below the freeze-out temperature for silicon, the photogenerated electrons can tunnel through the barrier, and the sensor recovers the same sensitivity as that obtained at room temperature.

Synthesis of zinc oxide (ZnO) nanostructures is reported by electrochemical deposition from an aqueous electrolyte in presence of graphene oxide (GO) with varying oxidation degree. The properties of hybrids were investigated by scanning electron microscopy, X-ray diffraction, Raman, Fourier-Transform Infrared and X-ray photoelectron spectroscopy techniques and photocatalytic measurements. The results indicated the electrodeposition of ZnO in presence of GO with increased oxygen content led to marked differences in the morphology while Raman measurements indicated an increased defect level both in the ZnO and the electrochemically reduced GO (ErGO) within the hybrids. The decrease in C/O atomic ratio of GO (from 0.79 to 0.71) employed for the electrodeposition of ZnO resulted in an increase in photocatalytic efficiency for methylene blue degradation under UV irradiation from 4-folds to 10-folds with respect to non-hybridized ZnO. The observed synergetic effect of cathodic deposition potential and oxygen content in GO towards improving the photocatalytic activity of immobilized ZnO is expected to contribute to further development of more effective deposition approaches for the preparation of high performance hybrid nanostructures.

Anomalous Hall effect is commonly used as a simple technique to study the magnetization reversal of perpendicularly magnetized thin films. Yet, in most applications, the easy-magnetization direction is in the film-plane. We here propose photo-induced anomalous Hall effect as a new magneto-metric technique to reconstruct the in-plane magnetization loop of metallic thin films. Nickel thin films were deposited on intrinsic silicon to form a Schottky contact. Photo-induced Hall voltage was found hysteretic with the in-plane, magnetic field. The measured voltage-loop was found to mimic the magnetization loop as measured by a magnetometer.

Iron oxide magnetic nanoparticles (MNPs) coated with uniform silica shell were synthesized through thermal decomposition and inverse microemulsion methods. The iron oxide MNPs were further coated with silica shells through hydrolysis reaction. For the resulting core–shell MNPs, size regulation of both the magnetic core and the porous shell were achieved, enabling the modulation of their magnetic properties and magnetic interactions. Core–shell MNPs were finally functionalized with amine groups, and immobilized on gold surface due to charge-neutral amine/gold interactions. It was observed that the immobilization process was enhanced under external magnetic field.

Lateral effect photodiodes sense the position of a laser beam by measuring the change of current between opposite anodes and a common cathode. They either require a bias current or the current is photogenerated. In either case, their linearity is affected by the non-uniformity of the current distribution between the anodes. We here propose a bias-free, lateral photo-diode, which consists of a resistive layer forming an extended Schottky contact to an intrinsic semiconductor. In our sensor, the photo-generated carriers do not diffuse laterally. Rather, their localization under the laser-beam results in a reduction of the barrier height due to image force effect. An open-circuit voltage appears between two opposite electrodes that is linear with the laser-beam position. A tetra-lateral configuration, with four anodes at the edges of a square-shaped sensor, allows sensing in two dimensions.

Organic complementary inverters that have high performance, low-power operation, and flexible compatibility are achieved using a simple and low-cost method to prepare a thin low- ${k}$ polymer dielectric on sputtered C nanoparticles. The operation voltage of the flexible inverter can be as low as 3 V, and the gain is close to 200, which is superior to most reported organic-based inverters. The flexible inverter also exhibits outstanding switching stability in multiple signal processing. The present organic inverters may be of value in portable and wearable electronics.

The exchange-coupled bilayers containing antiferromagnetic (AF) Cr2O3 have potential applications in novel spintronic devices with magneto-electric properties. The microstructures and magnetic properties of ion-beam sputtered NiFe/Cr2O3 bilayers are comparatively investigated at different Cr2O3 thicknesses on single-crystalline SrTiO3 (STO) (001) and amorphous SiO2 substrates. The formation of Cr2O3 is verified by X-ray photoelectron spectrometry. X-ray diffraction reveals a distinction in the preferred orientation of Cr2O3 deposited on different substrates. The variations in microstructure are responsible for the higher exchange bias, larger coercivity, and higher temperature stability of magnetization for samples grown on STO substrates. The coercivity and exchange bias at 10 K increases with Cr2O3 thickness. Higher Cr2O3 thickness also results in higher surface roughness, higher irreversibility temperature, and increased peak temperature of the out-of-phase AC susceptibility. This work has revealed the thickness dependence of the microstructure and magnetic properties of NiFe/Cr2O3 bilayers prepared on STO substrate. The outcome of this work may provide some insight for developing novel spintronic devices containing Cr2O3 and perovskite oxides.

Because of its low-cost, silicon is the standard material for photovoltaic conversion. Yet, its band-edge absorption spectrum is narrower than the spectrum of the solar radiation, which reduces its conversion efficiency. In this paper, it is shown that the spectrum of absorbance of silicon can be extended to longer wavelengths by proximity to a two-dimensional (2D) semiconductor. Photo-induced Hall effect, together with standard absorption spectroscopy, was employed to estimate the increase of photo-conversion efficiency of a 2D-platinum-diselenide/intrinsic-silicon heterostructure. The system shows a significantly higher absorption in the infrared as compared to the single films. Angle resolved X-ray Photoelectron Spectroscopy (XPS) confirm that a change of the band structure occurs in the silicon substrate at the interface between the two semiconductors. The results are interpreted in the framework of band-gap narrowing due to hole-confinement in the Si, induced by electron-confinement in the 2D film. This allows us to claim that the increase of photo-conversion efficiency in the Pt/PtSe2/Si sample is due to an enhancement of the light absorbance of silicon near the interface. Possible application of the effect in photo-voltaic cells is discussed.

Novel hybrid core-shell nanoarchitectures were fabricated by a simple two-step electrochemical approach: first ZnO nanorod core was electrodeposited from Zn(NO3)2 solution; further, the core nanoarray was coated with a shell based on polypyrrole hybridized with graphene oxide by electropolymerization. The properties of the core/shell nanoarchitectures were studied as a function of the core properties induced by electrodeposition parameters. The ZnO nanostructures showed improved crystallinity and c-axis preferred orientation with increasing cathodic deposition potential while the increased deposition duration resulted in a morphology transition from nanorod to pyramidal shape. The electrochemical activity of the core/shell arrays was found to increase with the deposition potential of ZnO core but decreased when morphology changed from nanorod to pyramid shape. The photocatalytic results showed improved activity for the core/hybrid shell nanoarrays with respect to ZnO and ZnO/PPy ones. The degradation rate for methylene blue decreased with prolonged deposition duration of the core. The obtained results highlight the importance of electrochemical tuning of ZnO-based core/shell nanoarrays for improved performance in electrochemical and photocatalytic applications.

Novel hybrid architectures based on ZnO nanostructures supported on reduced graphene oxide films are reported by a facile two-step aqueous electrochemical approach. Graphene oxide (GO) obtained by oxidizing graphite with either H2SO4:H3PO4 mix or H2SO4 was subjected to electrochemical reduction (ErGO) by constant potential and sweeping potential methods and further employed as seeding layer for electrodeposition of ZnO nanorods. The results showed the GO reduction rate was markedly influenced by oxygen content while Infrared spectroscopy indicated the sweeping potential was effective in removing the carbonyl and alkoxy groups but also as more defect-inducing reduction approach than constant potential, according to the Raman measurements. The subsequent electroreduction of ErGO during the electrodeposition of ZnO resulted in interfacial interaction between the seed layer and ZnO nanorods. H2SO4:H3PO4 mix induced a less disrupted graphitic plane in GO which proved beneficial for the growth of higher density ZnO nanorods with improved crystalline quality. By controlling the chemical introduction/electroreduction conditions for oxygen groups in GO materials, the interfacial interaction with ZnO nanorods and their properties could be tailored in order to obtain high performance nanoplatforms.

The photo-spin-voltaic effect is revealed by the presence of a spin voltage generated by photons when a non-magnetic metal (e.g., Pt) is in close proximity to a ferrimagnetic insulator (e.g., Y3Fe5O12 (YIG)). This is attributed to the excited electrons and holes diffusing from the proximized layer near the interface to the metallic surface. By using a dual-ion-beam sputtering deposition technique, a metallic PtMn layer was deposited on YIG /Gd3Ga5O12 (GGG) (111) substrates. We report on the photo-induced-spin voltaic effect in a PtMn/YIG/GGG heterostructure. The sign of the photo-generated voltage was found to switch with magnetic field polarity and its intensity to decrease with increasing PtMn thickness. This indicates that spin-polarized electrons are confined near the interface in the metal. Photo-excitation of these carriers, together with spin–orbit coupling with Pt atoms, is at the origin of the measured transverse voltage. The design may find applications in antiferromagnetic spintronics.

Exchange-coupled ferromagnetic/antiferromagnetic (FM/AF) bilayers are widely used in spin valves, magnetic tunnel junctions and spin–orbit torque devices. While most studies focused on AF layers exchange coupled with single FM layer, the exchange interaction with FM multilayer were not well understood. In this work, [Co/Ni]n/PtMn multilayers with different PtMn thickness were prepared. Polycrystalline face-centered cubic Co, Ni, and PtMn phases were evidenced by the grazing incidence x-ray diffraction measurements. At room temperature, the [Co/Ni]n/PtMn multilayers show similar soft ferromagnetism as the reference [Co/Ni]2 layers. Reducing the temperature results in broadening of the hysteresis loops, and exchange bias was not observed until 100 K. Temperature-dependent DC magnetization and AC susceptibility revealed blocking temperatures of 210–240 K and a spin freezing temperature of 140 K. This work has revealed the temperature evolution of exchange interaction in [Co/Ni]n multilayer interfacing with A1-phase PtMn. The results are important for understanding the physical process of the establishment of exchange coupling in various FM/AF interfaces.

The Hall-effect in semiconductors has been used for more than one century to measure the intensity of magnetic fields. While Hall sensors have been replaced by magnetoresistive sensors in digital systems, they still retain two features which make them preferable to the latter in analog applications: they are intrinsically linear because they do not make use of magnetic materials and their sensitivity is directly proportional to the bias current J through the charge velocity v. Yet, the latter of these features is more theoretical than practical. Commercial Hall sensors are engineered to work at a specific, and very low, bias current because Joule heating severely compromises their linearity. The Hall effect exists in metals, where the low resistance to electrical current would make Joule heating be negligible. Yet, so would be the transverse voltage. We engineered a system in which the Hall effect in a metal is greatly enhanced and Joule heating suppressed [1]. The device recovers tunable sensitivity, without compromising linearity, by replacing current bias with light bias. Our system consists of an extended metal/semiconductor junction, where the metal is highly transparent to light and forms a Schottky interface with the semiconductor (see figure 1). Light reaching the interface is the driving force to diffuse carriers across the bilayer. A magnetic field applied in the junction plane exerts a magnetic force on the carriers diffusing in the metal, which accumulate on opposite sides, according to their sign. This charge accumulation can be detected as an open-circuit voltage transverse to the metal. The voltage is proportional to the field strength, as well as to light intensity. At equilibrium, the net current is zero and no Joule heating is produces, regardless light intensity. In order to demonstrate this effect, we deposited three metallic films, platinum (Pt), gold (Au) and aluminum (Al) with thickness t = 3 nm on 1 × 1cm2 un-doped (100) silicon (Si) dice. These metals were chosen because they have progressively lower work-functions $( \Phi _{\mathrm {Pt}} =5.9$ eV, $\Phi _{\mathrm {Au}} =5.5$ eV and $\Phi _{\mathrm {al}} =4.20$ eV)6. A Si dye and a sample consisting of Pt with the same thickness deposited on insulating sapphire, α-Al 2 O 3 were used as references. The magnetic field was generated by using an electromagnet. The voltage was measured by connecting the midpoints of two opposite edges of the metallic film to a voltmeter. a controlled light source consisting of a bulb lamp and a manual shutter were employed. The bulb lamp emitted unpolarized light with a spectrum that covers all and only the visible range from 450 nm (violet) to 750 nm (red). One can see from Figure 1 that no voltage appears when a Si dye is used, which excludes that the effect is due to photo-Hall effect in the semiconductor [2]. Similarly, no signal was detected on a Pt/sapphire chip, which excludes that the voltage is due to excitation of electrons in the Pt. One can also see that the effect diminishes with decreasing work-function, which suggests that the establishment of a Schottky barrier is a necessary condition for the effect to exist and that light is absorbed in the space-charge layer of the junction. The experiment was repeated by using optical polarizers. The voltage signal was found to be insensitive to light polarization, which excludes any contribution from optical-Hall effect or photo voltaic-Hall effect [3]. For Pt and Au, the effect was found to be strongly linear with both magnetic field strength and light intensity. Similarly the voltage increased linearly with light intensity for fixed values of magnetic field. The current-voltage $( I_{S} /V_{S})$ characteristics across the metal/Si interfaces were measured by placing the electric contact on the Si as close as possible to the edge of the metal. As expected, the $I_{S} / V_{S}$ was found to be Schottky-like, strongly dependent on the light and independent on the magnetic field. The experimental evidences lead us to draw the following scenario. Metals with high work-functions form a Schottky contact with the semiconductor. A space-charge region arises in the semiconductor, near the interface. If the light penetration depth through the metal is longer than the film thickness, photons can be absorbed and charge can overcome the Schottky barrier, hence be injected into the metal. More specifically, once an electron-hole is photo-generated in the Si, the hole crosses the space-charge region to recombine with an electron in the metal and an electron crosses the space charge region to replace the recombined electron. In the Hall configuration of figure 1, no net current flows and the effect is strictly confined near the interface. Yet, electrons and holes diffusing across the space charge region are accelerated by the high built-in electric field and acquire a substantial velocity. The force F = qv × B exerted by the magnetic field is large because so is v. This is what makes the effect giant. The magnetic field bends the trajectory of the charge and an imbalance of charge appears at the edges of the metal. The voltage is detected in open-circuit conditions and no bias current across the junction. Therefore, no Joule heating is produced. The system shown here can reach the same sensitivity of a standard Hall-sensor but has a linearity-error that is independent on sensitivity because no Joule heating is produced.

The Hall effect in metals is too small to have practical applications. Instead, the same effect in semiconductors is the standard for magnetic field sensing. Yet, in semiconducting Hall-sensors, Joule heating severely compromises the linearity range. We here show that a Hall effect can be photo-induced in metals used for bias-free magnetic sensing. The system consists of a transparent metal that forms a Schottky contact to a semiconductor. Light reaching the interface results in the injection of charge from the space charge region. If a magnetic field is applied, a transverse, open-circuit voltage appears at the metal edges that is proportional to the field, as well as light intensity. The system shows sensitivities that are comparable to semiconducting Hall-sensors but no net current flows, therefore its performances are not affected by Joule heating.

Facile synthesis of ZnO nanorod core and polypyrrole shell arrays by electrochemical constant current deposition mode is reported. The effects of electrosynthesis parameters for polypyrrole (PPy) shell and its hybridization with graphene oxide (GO) on the structure, morphology and electrochemical properties of the core-shell arrays were analyzed. The results indicated a synergetic effect towards improving the electrochemical properties by tailoring the interfacial surface in ZnO/PPy core-shell arrays. High retention ratio (66 %) and an increase in voltammetric charge stored at inner surface (80 %) were exhibited by the ZnO/PPy-GO core/hybrid shell arrays with respect to ZnO/PPy ones.

sp–d exchange interaction was used to narrow the room-temperature band gap of zinc oxide films prepared by sol–gel method. Zinc oxide was doped with manganese ions by adding manganese chloride to the precursor and post-annealing in hydrogen. Films with different concentrations of manganese were prepared. Exchange interaction was established between the manganese ions in the lattice by introducing oxygen vacancies. The magnetic moment was found to increase with the concentration of manganese. For low concentrations of manganese, the band gap of the doped semiconductor was found to be wider than that of undoped ZnO films, in agreement with Vegard’s law. High concentrations of dopant resulted in a narrowing of the band gap. We ascribe the narrowing of the band gap to conduction band-edge Zeeman shifting. 12 at.% Mn was successfully substituted in ZnO films deposited by sol–gel method. Exchange interaction was established between the Mn ions through the mediation of oxygen vacancies. A narrowing of the band gap of ZnO was achieved by Zeeman shifting of the bottom of the conduction band.

Graphical abstractDisplay Omitted Size-controllable surface functionalized magnetic nanoparticles are obtained.Products show good dispersity in both DI water and PBS solution.Amphiphilic co-polymer coating enabled particles' bio-binding ability.Products are superparamagnetic with high Ms value at room temperature. With the advances in micro-/nano-electronic technology, the development of portable lab-on-chip biodetection device by utilizing magnetic nanoparticles as bio-probes and magnetic field sensor as signal detector has attracted considerable interests in healthcare area. Magnetic probes with required sizes are crucial in quantitative magnetic bio-detection for specific bio-analytes. The objective of this study was to synthesize and characterize amphiphilic co-polymer coated magnetic iron oxide nanoparticles with tunable sizes and study their bio-binding ability. Transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier transform infrared spectrometer (FT-IR), thermogravimetric analyzer (TGA), and vibrating sample magnetometer (VSM) were employed to investigate the particle dimension, hydrodynamic size, surface property, mass ratio of surface surfactants, and magnetic behavior. The investigation on their biologically binding ability with bovine serum protein was carried out on thin gold film. The results showed iron oxide nanoparticles with controllable sizes were coated by amphiphilic co-polymer successfully and could be completely transferred and well-dispersed in aqueous solutions. The final products with magnetic core sizes ranging from 6nm to 17nm showed superparamagnetic behavior, stable hydrodynamic sizes in aqueous suspensions, and binding ability with bio-molecules, making them promising candidates as magnetic tags for the development of bio-detection devices.

The vortex state is one of the equilibrium configurations of soft magnetic materials and occurs in thin ferromagnetic square and disk-shaped elements of sub-micrometer size. The vortex state has a specific excitation mode: the in-plane gyration of the vortex structure about its equilibrium position. This mode can be electrically excited by a spin-polarized current. When the gyrating vortex reaches a critical velocity, a switching of the vortex core can occur. We show here how to increase the vortex velocity to reduce the switching current. The vortex core can be switched back by reversing the current direction.

Spin transfer torque oscillators based on magnetic vortex precession can deliver output powers large enough for practical applications. In addition they do not require discrete electronic components, such as capacitors or inductors, to tune the oscillation frequency. At the current stage, this oscillation frequency is still too low and can be increased only by trading off the output power. Here, we present our experimental results on nanocontact oscillators, which are, amongst the spintronic oscillators, those that can deliver the largest power. Based on the analysis of our experimental results, we propose a new device geometry and numerically demonstrate that an increase of the frequency, up to a useful range for practical applications, can be obtained without trading off output power.

Multifunctional, Fe-doped indium tin oxide (ITO) nanostructured films were grown by pulsed laser deposition on sapphire substrates. The films showed low resistivity and n-type conductivity with a carrier density as high as $3\times 10^{21}~{\rm cm}^{-3}$ . A magnetic moment at room temperature larger than those of any iron oxides was measured in films with Fe doping as low as 2%. We ascribe it to the formation of bound polarons. A strong green photoemission at room temperature was observed, which we ascribe to quantum confinement effect. The coexistence of ferromagnetism and luminescence in the visible range makes our films of potential for magneto-optoelectronic applications.

Gold/iron oxide nanocomposites offer the promise of combining the unique traits of both gold and iron oxide nanomaterials to enable new applications. In this work, a simple and safe method has been established whereby the morphology of gold material in gold/iron oxide nanocomposites can be controlled to be nanowire or nanosphere by adjusting the initial molar ratio of citrate-coated iron oxide nanoparticles to auric acid. Gold/iron oxide nanowires and nanospheres were synthesized through this method. Their structural, optical, and magnetic properties were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), dynamic light scattering (DLS), ultraviolet-visible spectroscopy (UV-Vis), and vibrating sample magnetometry (VSM). These materials substantially maintained the optical properties of gold nanomaterials and magnetic features of iron oxide magnetic nanoparticles.

Extended Abstract Memristive switching in oxide semiconductors relies on the formation and disruption of conductive nano-filaments [1]. This effect is considered promising for the next generation of non-volatile memories. Yet, the switching event is a complicated electronic and ionic process, which may involve more than one mechanism. In order to elucidate the switching mechanism, advanced microscopy investigations proved challenging because of heavily dependence of the results on specimen preparation techniques. Important information can be obtained if switching leads to a macroscopic change of nonelectrical properties, for instance magnetic properties. In this respect, n-type Mn-ZnO and p-type NiO provide a unique testbeds since the magnetic properties of these oxides are strongly dependent on the distribution of oxygen vacancies [2]. We show that resistive switching in n-type ferromagnetic Mn-ZnO and p-type antiferromagnetic NiO coexists with a switching of the magnetic phase. Thin films of these oxides were sandwiched between two metallic electrodes and resistive switching was induced. Nano-devices were patterned out of the trilayers by resorting to electron beam lithography and physical etching. We found that a switching of the resistance corresponds to a switching of the magnetic phase in the film [3, 4]. By measuring the magnetic properties of the devices in the two resistive states, we can draw important conclusions on the underlying switching mechanism. For instance, in Mn-ZnO the effect is not filamentary type and occurs uniformly under the interface, whereas in NiO the effect is filamentary type. By measuring the change of magnetic properties we could exclude that switching was due to the formation of Ni-ion filaments across the device. We have demonstrated [4] that the switching is due to the formation and rapture of oxygen-vacancy filaments.

We have investigated the origin of the ferromagnetic ordering in undoped and Mn-doped ZnO thin films. A systematic comparison is presented between two sets of films grown by pulsed laser deposition from targets prepared under the same conditions. We show that ferromagnetic ordering in both compounds is directly related to the concentration of oxygen vacancies. The incorporation of Mn dramatically increases the magnetic moment in highly oxygen-deficient films. By analyzing the photoluminescence spectra and the structural properties of the films, we can exclude that magnetic ordering in our films originates from unintentional doping.

Magnetic vortex-based oscillators represent a unique opportunity to study the mutual spin-transfer torque coupling between two ferromagnetic layers in a spin-valve configuration. This will eventually lead to a complete understanding of this phenomenon and, potentially, to electronic devices of practical application. Mutual spin-transfer torque can lead to multiple-mode high-frequency dynamics in a spin-valve system. We here report our study on the emission response of an ohmic nanocontact to a spin-valve multilayer subject to perpendicularly applied magnetic field. In this configuration, three modes are accessible, two of which correspond to the precessional motion of a vortex in one of the two ferromagnetic layers with the other working as a static polarizer. At high currents, the third mode can be observed that is ascribed to the simultaneous precession of two vortices, one in each layer, with the other layer working as a dynamic polarizer. The simultaneous application of a field in the sample plane tends to suppress the mode that corresponds to the precessional motion of the vortex in the thinner ferromagnetic layer.

In an elliptical magnetic dot two vortices and a flower state configuration can be accommodated at remanence. We show that a two-fold degeneracy in the position of the flower state can be geometrically introduced and exploited for solid state data storage. Switching between two, energetically-equivalent, magnetic configurations is obtained by injecting a perpendicular electric current. Switching currents of the order of ~105 A/cm2 and high thermal stability are demonstrated by micromagnetic simulations. This system can be used as a bit-cell for magnetic solid state data storage. The low value of the switching current and the high thermal stability allow direct integration with the current complementary metal oxide semiconductor technology.

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.

Synchronized spin-valve oscillators may lead to nanosized microwave generators that do not require discrete elements such as capacitors or inductors. Uniformly magnetized oscillators have been synchronized, but offer low power. Gyrating magnetic vortices offer greater power, but vortex synchronization has yet to be demonstrated. Here we find that vortices can interact with each other through the mediation of antivortices, leading to synchronization when they are closely spaced. The synchronization does not require a magnetic field, making the system attractive for electronic device integration. Also, because each vortex is a topological soliton, this work presents a model experimental system for the study of interacting solitons.

The studies of the effects of magnetic field on surface enhanced Raman scattering (SERS) have been so far limited to the case of ferromagnetic/noble-metal, core/shell nano-particles, where the influence was always found to be negative. In this work, we investigate the influence of magnetic field on a diluted magnetic semiconductor/metal SERS system. Guided by three dimensional finite-difference time-domain simulations, a high efficient SERS substrate was obtained by diluting Mn into Au-capped ZnO, which results in an increase of the dielectric constant and, therefore, an enhancement of Raman signals. More remarkably, an increase of intensities as well as a reduction of the relative standard deviation (RSD) of Raman signals have been observed as a function of the external magnetic strength. We ascribe these positive influences to magnetic-field induced nucleation of bound magnetic polarons in the Mn doped ZnO. The combination of diluted magnetic semiconductors and SERS may open a new avenue for future magneto-optical applications.

Hybrid nanostructure can inherit the physiochemical properties of its individual components to realize its multi-functionality. The coupling of plasmonic effect of gold nanoparticles with magnetic properties of iron oxide nanoparticles has shown great promise as bi-functional agents allowing simultaneous magnetic resonance imaging (MRI)/ computed tomography (CT) imaging and magnetic/photonic thermal therapy.[1, 2] However, since gold and iron oxide are two dissimilar materials, the precise morphology and structure control for the hybrid nanostructure remains a great challenge, and there are few published studies on the correlation between composites morphologies and the optical/magnetic properties. In this work, we aim to fabricate gold/iron oxide hybrid nano-structures using less toxic precursors, control the morphology growth of iron oxide component on gold nanoparticles surface, and study the effects on optical and magnetic properties of final products. Here, nearly monodisperse gold/iron oxide hybrid nanoparticles were fabricated through thermal decomposition method. (Fig. 1a-1f) Spherical gold nanoparticles were pre-synthesized and used as seeds for the reduction of iron precursor to produce hybrid nanostructures. Various morphologies of iron oxide grown on the gold nanospheres surfaces were realized, including nano-shell, nano-octahedron, nano-flower, and dumbbell-shaped end. (Fig. 1c-1f) Pure gold nanospheres and iron oxide nanospheres were synthesized for comparison. The morphology and structure of obtained products were characterized by using TEM, EDX, electron diffraction pattern, and SEM. Their optical and magnetic properties were studied using UV-Vis spectroscopy and VSM. The plasmonic property of gold nanoparticles was shown to be affected by the optical index of its environment, and its absorbance peak was right-shifted after iron oxide shell coating. (Fig. 2a) The gold/iron oxide dumbbell-shaped nanostructures displayed typical superparamagnetic behavior with no coercivity (Fig. 2b), while the coercivity of gold/iron oxide nano-octahedron was about 45 Oe (inset in Fig. 2b). The morphology-related blocking temperatures of the gold/iron oxide nano-structured samples were also studied through their ZFC/FC curves.

We report a large negative magnetoresistance in Manganese-substituted Zinc Oxide thin films. This anomalous effect was found to appear in oxygen-deficient films and to increase with the concentration of Manganese. By combining magnetoresistive measurements with magneto-photoluminescence, we demonstrate that the effect can be explained as the result of a magnetically induced transition from hopping to band conduction where the activation energy is caused by the sp-d exchange interaction.

We investigated the role of strain on the magnetic properties of La0.7Sr0.3MnO3 epitaxial films grown on substrates with different crystallographic orientation. The magnetic characterization confirms the large magnetostriction due to the tensile stress applied by the SrTiO3 substrates. The data demonstrate that the easy direction of magnetization is aligned to the elongated, in-plane axis both in (110)- and (001)-oriented films. The in-plane anisotropy of (110) films is interpreted in the frame of a simple structural model. We provide evidence of a spatial separation between a conducting ferromagnetic and an insulating paramagnetic phase at the Curie temperature. The possible effect of such phase separation on the coercitive field and on the magnetization versus temperature is discussed. (c) 2006 Elsevier B.V. All rights reserved.

Polymer-embedding of nano-sized indium tin oxide (SnO center dot In2O3, ITO) produces electrically conductive materials transparent to the visible light at filling factors higher than the percolation threshold. ITO powders are commercially available in an aggregated form and a disaggregation technique was required. Here, aggregated ITO nanoparticles were transformed to colloidal suspension by high-speed stirring. This finely dispersed ceramic suspension was stabilized by addition of poly(vinyl pyrrolidone) and the obtained colloidal system was cast on an optical-grade substrate (PET) to produce electrically conductive-transparent nanocomposite films. Preliminary mechanical and electrical characterization of these films showed good conductivity and interfacial properties.

Checking the effect of focused Ga ion beam (FIB) irradiation on a target at very low dose is still a challenge. High-resolution magneto-optical microscopy and scanning electron microscopy (SEM) are used to investigate weakly irradiated tracks patterned by FIB on a Pt/Co(1 nm)/Pt ultrathin ferromagnetic film. The two techniques give complementary results on surface film morphology and magnetism. Magneto-optical microscopy, linked to tiny ion rearrangements at interfaces, is found to be more sensitive than SEM to detect damages after irradiation at very low dose.

The critical Josephson current (IC) in superconducting/ferromagnetic (S/F) multilayer-based junctions can be controlled by changing the relative directions of the magnetization in the F-layers. Recent experimental works [1, 2] show that an enhancement of IC is achieved in S/F weak links when the alternating F-layers are antiparallel aligned. We present preliminary experimental results concerning the dependence of IC on the relative orientation of the ferromagnetic layers in S/F1/I/F2/S tunnel junctions where the F-layers are obtained by changing the relative composition of NiCu alloys. The multilayers were grown by electron beam deposition, and processed by Focused Ion Beam lithography. The magnetic state of the devices was directly determined by measuring the current perpendicular to plane (CPP) magnetoresistance (MR) at high bias. IC was found to be larger when the F-layers are antiparallel aligned. The maximum change of IC corresponds to the maximum change of MR. The application of a magnetic field induces a transition in the shape of the currentvoltage curve that seems to suggest Coulomb blockade effect.

We present experimental results concerning both the fabrication and the characterization of superconducting tunnel junctions based on Nb/NiCu superconductor/ferromagnet (S/F) bilayers. Josephson junctions have been characterized down to T=1.4 K in terms of current-voltage I-V characteristics, Josephson critical current vs magnetic field, role of external magnetic field. Proximity parameters of the bilayer, such as the coherence length and the exchange field energy of the F metal, have been estimated by means of a numerical deconvolution of the I-V data the electronic density of states on both sides of the S/F bilayer. Results have been compared with theoretical predictions from a proximity model for S/F bilayers in the dirty limit in the framework of Usadel equations for the S and F layer, respectively.

The dependence of the critical Josephson current (I-C) and magnetoresistance (MR) on the relative orientation of the ferromagnetic layers is investigated in current perpendicular to plane (CPP) measurements of superconductor/ferromagnetic (S/F) multilayers. Two different CuxNi1-x alloys were chosen so that alternate F-layers reversed at different applied magnetic fields and that the ferromagnetic coherence length was of the order of several nanometres. These structures show a significant CPP high-bias MR, which enables the magnetic state of the devices to be determined directly. We found that I-C is substantially larger when the adjacent F-layers are aligned antiparallel compared to the case of parallel orientation. Since in a pseudo-spin-valve structure the relative F-layer orientation is approximately parallel for zero applied magnetic field, I-C can experience an enhancement when a magnetic field is applied in the plane of the junction. The maximum change of I-C corresponds to the maximum change of MR.

The methods of superconducting device fabrication by lithography and multilevel processing usually require a number of processing steps with lithographic resolution and alignment adequate for the scale of the device be fabricated. As an alternative, the focused ion beam (FIB) microscope is increasingly being used directly to fabricate devices. A major advantage of using a FIB compared to other lithography methods is its flexibility and high resolution. It allows in-situ, milling (∼5 nm at a beam current of 1 pA) to a variety of depths, and imaging (2 nm) of the sample. In this paper we describe our development of junction fabrication techniques using the FIB and their application in creating a range of potential sensor devices and quantum electronics applications. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Perpendicular magnetic anisotropy (PMA) was studied at low temperature (T=30 K) in dc-magnetron sputtered Ni60Cu40/Cu multilayers. PMA has been observed in many multilayer structures for ferromagnetic layer thicknesses less than a certain thickness t⊥. In general cases t⊥ is less than a few nanometers, making such structures unsuitable for low-cost fabrication techniques. Our results show a strong perpendicular easy direction of magnetization for NiCu layer thickness between 4.2 nm and 34 nm. The thickness t⊥ at which the multilayers change the preferential orientation from perpendicular to in-plane is estimated to be 55 nm. Structural studies show that the low magnetostatic energy density is likely to be the main reason for the large t⊥ value obtained in this system.

Spin orbit coupling in heavy metals allows the conversion of unpolarized light into an open-circuit voltage. We experimentally prove that this photo-spin voltaic effect is due to photo-excitation of carriers in the proximized layer and can exist for light in the visible range. While carrying out the experiment, we discovered that, in closed-circuit conditions, the anisotropic magnetoresistance of the proximized metal is a function of the light intensity. We name this effect photo-magnetoresistance. A magneto-transport model is presented that describes the change in magnetoresistance as a function of the light intensity.

Magnetic skyrmions are envisioned as ideal candidates as information carriers for future spintronic devices, which have attracted a great deal of attention in recent years. Due to their topological protection, the creation and annihilation of magnetic skyrmions have been a challenging task. Here, we numerically demonstrate that a magnetic skyrmion can be created by chopping a chiral stripe domain with a static uniaxial strain/stress pulse. This mechanism not only provides a method to create skyrmions in magnetic nanostructures but also offers promising routes for designing tunable skyrmionic-mechanic devices.

We present novel low-field magnetoresistive devices based on the ferromagnetic manganite La0.7Sr0.3MnO3 operating in the current in plane (CIP) configuration. In these planar spin-valve devices, a focused Ga+ beam is used to create pinning centers for magnetic domain walls. The spin-dependent scattering of polarized electrons at the domain walls (DW) is responsible for the magnetoresistance observed in the patterned tracks. The magneto-transport properties of these devices are interpreted within a model for DW magnetoresistance. Applications such as magnetic data storage can be envisaged for the structures we investigated. (C) 2006 Elsevier B.V. All rights reserved.

Band engineering of transparent semiconductors, such as TiO2, SnO2, has recently been attempted to become black colour in order to increase photocatalytic efficiency in the visible and near infrared ranges. Here, we investigated a previously-neglected property in black oxides by using the example of iron doped indium tin oxide nanoparticles: the photo-thermal effect in the visible and near-infrared ranges. We found a significant enhancement of the photo-thermal generation in the near-infrared biological window that is due to photon absorption, with no significant contribution from surface plasmon resonance. This allows independent magnetic functionalization of the particles by iron doping. These particles may be used for in-vivo cancer treatment where heat is photo-termally generated, while keeping the magnetism as a mean for remote manipulation through permanent magnets.

International audience; Magnetic vortex dynamics in thin films is characterized by gyrotropic motion, the sense of gyration depending on the vortex core polarity, which reverses when a critical velocity is reached. Although self-sustained vortex oscillations in nanoscale systems are known to be possible, the precise role of core reversal in such dynamics remains unknown. Here we report on an experimental observation of periodic core reversal during self-sustained vortex gyration in a magnetic nanocontact system. By tuning the ratio between the gyration frequency and the rate of core reversal, we show that commensurate phase-locked and incommensurate chaotic states are possible, resulting in Devil’s staircases with driving currents. These systems could have the potential to serve as tunable nanoscale radiofrequency electrical oscillators for secure communications, allowing schemes such as encryption by chaos on demand.

The magnetic properties of hematite (?-Fe2O3) nanoparticles synthesized by in situ thermal decomposition of an iron-mercaptide precursor in polymeric matrices are studied. In Polystyrene, nanoparticles with average size ~20 nm can be produced that show ferromagnetic behavior with no Morin transition for temperatures as low as 10 K. Poly(9-vinylcarbazole)-based nanocomposites, produced by the same synthesis process, show a different magnetic behavior with a clear Morin transition. The effect of the polymeric matrix on the structural and magnetic properties of dispersed hematite nanoparticles is discussed. It is concluded that, in heavily viscous medium, the ability to control the particle growth and distribution is compromised.

We present a computational study of current-driven vortex dynamics in a particular geometry, a hybrid Co/Au/Py nanocontact, in which the Co layer is not flat. The experimental measurements validate the numerical results. We identify the Py layer as dynamically active. The nonuniform magnetization configuration in the Co layer, which acts as spin polarizer, and the interlayer magnetostatic stray field, both of which are mostly determined by geometry, are shown to have crucial influence on the dynamic properties of the system. The frequency as a function of current at zero field and also as a function of an out-of-plane field for a fixed current are computed. An excellent quantitative agreement with experimental data is obtained, demonstrating a novel approach for tailoring vortex nano-oscillators.