Understanding the stability of magnetic textures in multilayer patterned dots would constitute a significant step toward skyrmion-based applications. Here, we report the observation of skyrmions in patterned nanodots composed of multilayers. We examine the stabilization of various magnetic states such as single-domain states, skyrmion states, horseshoe-like domain structures, and worm-like domain structures in submicrometer dots (diameters 150–525 nm). Dots are fabricated from Pt/Co/Au multilayer structures that exhibit the interfacial Dzyaloshinskii–Moriya interaction and perpendicular magnetic anisotropy. In particular, we show that a stack of six repetitions of Pt/Co/Au layers suffices to stabilize the skyrmion state inside a dot at room temperature. A micromagnetic simulation determines the regime of skyrmion stability. The results reveal a correlation between the magnetic-force microscopy measurements and the micromagnetic simulation. Furthermore, we explain the development of the magnetic state with increasing dot diameter. We envision that nanopatterning of multilayer magnetic films could serve as a versatile way of creating magnetic skyrmion states.

We have developed a vortex-core magnetic force microscope (VC MFM) for magnetic field imaging at the nanoscale for many research fields-physics, biology, materials science, and metrology. The method solves principally quantitative scanning by increasing magnetic tip durability and introducing its calibration. We show that nature itself gives us a sharp, durable, and calibrated magnetic probe. It is represented by a narrow magnetic vortex core located in the center of a ferromagnetic disk placed at the apex of a scanning tip. Such a tip offers potentially high spatial resolution-the vortex core is magnetically sharp (the vortex diameter is<20nm for Permalloy), but at the same time, the disk is geometrically blunt and therefore durable. The magnetic moment of the vortex core is independent of the disk diameter and can be tuned smoothly by the disk thickness. We describe here the basic properties of the VC tip, its technology, and sensitivity to the magnetic field and show its durability. The first results obtained on hard disk drive are promising-from the analysis of data tracks, the spatial resolution of the VC tip is only a bit worse than the one of the standard MFM tips. We believe that the VC tip could be a sensor of choice for magnetic field imaging for scientific areas mentioned above.

Recent development of the magnetic material engineering led to achievement of the systems with a high interfacial Dzyaloshinskii-Moriya interaction (DMI). As a result, the formation of non-collinear magnetic soliton states or nonreciprocal spin wave dynamics is achievable. Typically used materials are based on bi-layers Heavy Metal/Ferromagnet, e.g., Pt/Co. These layers are characterized not only by a strong DMI, but also by the spin pumping effect and the resulting relatively large damping. Here, we show that the considerable interfacial DMI can be also present in bi-layers based on Ru/Co, characterized with low spin pumping effect and low damping. It is therefore a good candidate for the dynamical studies and implementations of chiral DMI. It is demonstrated by theoretical calculations that the value of DMI can be strongly affected and controlled by the strain of the lattice. We show a systematic experimental and theoretical comparison of magnetic material parameters between Pt/Co and Ru/Co bi-layers as a deserving candidate for spintronic and spin-orbitronic applications.

We have designed and implemented a dual-cantilever magnetometer, in which the coupling magnetic forces between the two cantilevers can be switched on/off by an external magnetic field. The coupling is realized by a pair of ferromagnetic ellipses, located on the cantilevers. One of the ellipses is "narrow" - it bears only a single domain magnetic state independently of the applied external field. The other one is "wide", and can be either in single-or closure-domain states depending on the applied field. In such configuration, the interacting force between the cantilevers can be attractive (both ellipses are in single domain state conforming to the external field), repulsive (both are in single domain states, but the narrow ellipse is in a meta-stable state, with magnetization opposite to the field) or switched off (when the closure domain state appears in the wide ellipse). We found that the coupling between the ellipses directly corresponds to the phase shift of the vibrating cantilevers. In this manner, the cantilever phase detection can be used to read out the magnetic state of the ellipses, which depends on the applied magnetic field. Moreover, we study how the magnetic state of the wide ellipse influences the flipping field of the narrow ellipse. Our observations are supported by micromagnetic simulations and by additional magnetic force microscopy experiments. We also discuss sensitivity and potential application of the magnetometer in future experiments. (C) 2017 Published by Elsevier B.V.

We studied the process of deposition of a thin nanocrystalline ZnO layer on vertical free-standing GaP nanowires (NWs). The paper presents the preparation of a new type of composite antireflection coating based on a compact GaP NW/ZnO layer structure. The NWs were prepared using metal organic vapour phase epitaxy. They were grown at Au seeds created from a similar to 0.3 nm thick Au layer, which was deposited on GaP substrate by evaporation. RF sputtering was used to cover the NWs and substrate with a ZnO layer with a nominal thickness between 50 and 250 nm. While thinner ZnO layers wrapped the NWs and covered the substrate, thicker ones also filled the volume between the NWs and the ZnO wrapping acquired a shape that resembled that of cotton swabs. A compact and planarized GaP NW/ZnO layer structure was achieved by altering ZnO deposition with ZnO etching by Ar ions. GaP NW/ZnO layer structures, which differed in the degree of ZnO filling, exhibited antireflection behaviour that was superioir to that of GaP substrate with GaP NWs. (C) 2016 Elsevier B.V. All rights reserved.

Self‐aligned normally‐off n++GaN/InAlN/AlN/GaN MOS HEMTs with a recessed gate show scalable threshold voltage between 1.3 to 3.7 V, which increases with the gate oxide thickness. Al2O3 or HfO2 gate insulators were grown by ALD at 100 °C so that one photoresist mask could be used for the gate recessing, ALD and metal lift‐off. A low density of the barrier surface donors ∼1 × 1013 cm−2 stems from the low thermal budged during the HEMT processing and explains the threshold voltage behaviour. Maximal IDS reaches ∼0.4 A/mm despite 2‐μm gate length and 8‐μm source‐to‐gate distance invariant to the threshold voltage. It is shown that for the present device Al2O3 provides better gate insulation than HfO2, however, the latter may be more appropriate for highly scaled short gate‐length HEMTs. Schematic picture of the self‐aligned InAlN/GaN MOS HEMT.

We studied vortex nucleation/annihilation process and its temperature dependence in micromagnetic objects with lowered symmetry using micro-Hall magnetometry. Magnetization reversal curves were obtained for the Pacman-like nanodots placed directly on Hall probes. Lowered symmetry of the object leads to good control of its chirality. Vortex nucleation and annihilation fields strongly depend on the angle of the external in-plane magnetic field with respect on the nanodot symmetry. The micromagnetic simulations support the experimental results - the vortex nucleation fields are controlled by local magnetization configurations present in the object (C-, S-, and double S-states) for field just above vortex nucleation field. The experiments also confirm that the vortex nucleation proceeds via thermal activation over an energy barrier.

Surface condition before an insulator deposition is the key issue for the preparation of reliable GaAs-based metal-oxide-semiconductor (MOS) devices. This study presents the preparation and properties of InGaAs/GaAs MOS structures with a double-layer insulator consisting of an oxygen-plasma oxide covered by Al2O3. The structures were oxidized during 75 s and 150 s. Static measurements yielded a saturation drain current of similar to 250mA/mm at V-G = 1V. Capacitance measurements showed improved performance in the depletion region compared with the structures without the double-layer insulator. Trapping effects were investigated by conductance vs. frequency measurements. The trap state density was in order of 10(11) cm(-2).eV(-1) with a continuous decrease with increased trap energy. The carrier mobility evaluation showed peak values of 3950 cm(2)/V.s for 75 s and 4570 cm(2)/V.s for 150 s oxidation times with the sheet charge density congruent to 2 x 10(12) cm(-2). The results demonstrate great potential of the procedure that was used to prepare the GaAs-based MOS devices with oxidized GaAs surface covered with an Al2O3 insulator. (C) 2014 AIP Publishing LLC.

In this work we systematically study the effect of the Al2O3 barrier layer thickness on the resistive switching properties of Al2O3/TiO2 bilayer grown by atomic layer deposition in the Pt/Al2O3/TiO2/TiN stacks. It was found that an Al2O3 layer of a certain thickness is essential to stabilize the resistive switching parameters while these can be further tuned by current compliance during SET. A two-step forming process was required to achieve stable repetitive bipolar switching loops. The endurance of 104 readings of alternating resistance states was obtained for structures with 3 and 4nm of Al2O3 during pulsed measurements. Forming was performed also at elevated temperatures using constant voltage stress. It was found that the switching is filamentary and happens in the Al2O3 layer while TiO2 is acting as an oxygen vacancy reservoir.

Atomic layer deposition was used for preparation of TiO2 and HfO2 thin films for resistive switching in metal-insulator-metal structures with Pt and TiN top and bottom electrodes, respectively. To obtain stable bipolar resistive switching loops in TiO2-based structures Al2O3 barrier with the thickness of 3 - 5 nm was necessary. HfO2-based structures with the insulator thickness less than 10 nm exhibited stable bipolar resistive switching. Ratio between high resistivity and low resistivity state varied between 20 and 100 depending on structure preparation and composition as well as on parameters of DC current – voltage measurement. Resistive switching effect was demonstrated in metal-insulator-metal structures with HfO2 layers thickness below 3 nm.

We have investigated the magnetization properties and flux dynamics of superconducting Cu$_x$TiSe$_2$ single crystals within wide range of copper concentrations. We find that the superconducting anisotropy is low and independent on copper concentration ($\gamma\sim1.7$), except in the case of strongly underdoped samples ($x\leq0.06$) that show a gradual increase in anisotropy to $\gamma\sim1.9$. The vortex phase diagram in this material is characterized by broad region of vortex liquid phase that is unusual for such low-$T_c$ superconductor with low anisotropy. Below the irreversibility line the vortex solid state supports relatively low critical current densities as compared to the depairing current limit ($J_c/J_0\sim10^{-7}$). All this points out that local fluctuations in copper concentration have little effect on bulk pinning properties in this system.

The embedding of metallic nanoparticles in the traditional optical materials (e.g. SiO2) gives us the possibility to create new optical materials. Metallic particles of nanometric dimensions can be transparent in wide spectral ranges of light. The incorporation of nanocrystal inclusions in such nanocomposites provides the benefit of targeted manipulations of their macroscopic optical response. In this paper we present the possibility to create, using vacuum deposition methods, the nanocomposite coatings with fairly small refractivity.

We present the study on the interlayer and intergranular exchange and dipolar coupling in [Fe97Si3/SiO2]5 discontinuous multilayers by means of ferromagnetic resonance. Due to strong ferromagnetic exchange coupling (J~-3 erg/cm2) the precessional motions of magnetic moments of granules are coupled and results in an acoustic and optical mode. Moreover there is notable line splitting in optical mode under external field normal to the layer, which is explained by an interlayer dipolar coupling, only possible for discontinuous layer. Some aspects of the damping processes in discontinuous multilayers are discussed as well.

The electric transport, magnetic, and magnetotransport properties of Fe-SiO2 nanocomposites prepared by Fe-ion implantation into silica were investigated. The structural studies revealed bcc Fe nanoparticles of an average size of 3 nm dispersed in a 100-nm-thick nanocomposite layer formed within the silica substrate. Using special thin-film electrodes that were only 100 nm apart, in-plane electrical measurements were performed in a temperature range of 4-300 K. Though no external gate electrode was used, single-electron transport phenomena (Coulomb blockade and Coulomb staircase) were observed at 4 K. The presence of Coulomb steps in I-V curves implies that the electric transport was realized by the tunneling of electrons via a random quasi-one-dimensional chain of a few isolated iron nanoparticles. The magnetic properties of the nanoparticles were determined by surface effects and by the superparamagnetic behavior. The nanoparticles exhibited enhanced anisotropy and were dipolarly interacting. However, the tunneling current was found to be independent of external magnetic field; i.e., no tunneling magnetoresistivity (TMR) was measured at 77 K. At this temperature the nanoparticles were superparamagnetic. Presumably, a low volumetric concentration of Fe nanoparticles (< 14%) and a spin-flip process due to residual single Fe atoms present in the silica barriers were responsible for the absence of the TMR effect.

We present a method which allows to visualize the critical current when it appears suppressed and is unmeasurable. The method is based on the integration of the zero-bias peak observed in the differential conductance vs. bias curves. We have utilized this method for the measurement of those parts of the critical current IC(T) and IC(Φ) dependencies which are not measurable in the conventional way. The method helps us reveal phenomena related to the existence of 0–π-state in the Nb–Fe0.1Si0.9–Nb-Josephson junction. In general, the method can be used for the analysis of Josephson junctions under the conditions where the critical current is extremely small, like close to the critical temperature or in high applied magnetic fields.

We have studied the temperature and field dependencies of the critical current I-C in the Nb-Fe0.1Si0.9-Nb Josephson junction with a tunneling barrier formed by a paramagnetic insulator. We demonstrate that in these junctions coexistence of both the 0 and the pi states within one tunnel junction occurs, and leads to the appearance of a sharp cusp in the temperature dependence I-C(T), similar to the I-C(T) cusp found for the 0-pi transition in metallic pi junctions. This cusp is not related to the 0-pi temperature-induced transition itself, but is caused by the different temperature dependencies of the opposing 0 and pi supercurrents through the barrier.

Electrical properties of Josephson junctions Nb/FeSi/Nb with superconductor/ferromagnet (S/F)interfaces are presented. Due to Andreev reflection the nearly exact quadruple enhancement of the tunnel junction differential conductance compared with that of the normal state was achieved. The transparency of the S/F interfaces in our junctions was estimated to be close to unity. This almost ideal value is obtained due to the use of a very smooth amorphous magnetic FeSi alloy for the barrier preparation. The real structure of the Nb/FeSi/Nb tunnel junction is described as a S/F/I/F/S junction. Also Nb/FeSi/Si/Nb Josephson junctions were investigated and the results found on these junctions confirm the effects observed in Nb/FeSi/Nb.