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Polymer microspheres can be fluorescently-coded for multiplexing molecular analysis, but their usage has been limited by fluorescent quenching and bleaching and crowded spectral domain with issues of cross-talks and background interference. Each bioassay step of mixing and separation of analytes and reagents require off-line particle handling procedures. Here, we report that stray magnetic fields can code and decode a collection of hierarchically-assembled beads. By the microfluidic assembling of mesoscopic superparamagnetic cores, diverse and non-volatile stray magnetic field response can be built in the series of microscopic spheres, dumbbells, pears, chains and triangles. Remarkably, the set of stray magnetic field fingerprints are readily discerned by a compact giant magnetoresistance sensor for parallelised screening of multiple distinctive pathogenic DNAs. This opens up the magneto-multiplexing opportunity and could enable streamlined assays to incorporate magneto-mixing, washing, enrichment and separation of analytes. This strategy therefore suggests a potential point-of-care testing solution for efficient kinetic assays.

Highly compliant electronics, naturally conforming to human skin, represent a paradigm shift in the interplay with the surroundings. Solution-processable printing technologies are yet to be developed to comply with requirements to mechanical conformability of on-skin appliances. Here, it is demonstrated that high-performance spintronic elements can be printed on ultrathin 3 µm thick polymeric foils enabling the mechanically imperceptible printed magnetoelectronics, which can adapt to the periodic buckling surface to be biaxially stretched over 100%. They constitute the first example of printed and stretchable giant magnetoresistive sensors, revealing 2 orders of magnitude improvements in mechanical stability and sensitivity at small magnetic fields, compared to the state-of-the-art printed magnetoelectronics. The key enabler of this performance enhancement is the use of elastomeric triblock copolymers as a binder for the magnetosensitive paste. Even when bent to a radius of 16 µm, the sensors printed on ultrathin foils remain intact and possess unmatched sensitivity for printed magnetoelectronics of 3 T-1 in a low magnetic field of 0.88 mT. The compliant printed sensors can be used as components of on-skin interactive electronics as it is demonstrated with a touchless control of virtual objects including zooming in and out of interactive maps and scrolling through electronic documents.

The main origin of the chiral symmetry breaking and, thus, for the magnetochiral effects in magnetic materials is associated with an antisymmetric exchange interaction, the intrinsic Dzyaloshinskii-Moriya interaction (DMI). Recently, numerous inspiring theoretical works predict that the bending of a thin film to a curved surface is often sufficient to induce similar chiral effects. However, these originate from the exchange or magnetostatic interactions and can stabilize noncollinear magnetic structures or influence spin-wave propagation. Here, we demonstrate that curvature-induced chiral effects are experimentally observable rather than theoretical abstraction and are present even in conventional soft ferromagnetic materials. We show that, by measuring the depinning field of domain walls in the simplest possible curve, a flat parabolic stripe, the effective exchange-driven DMI interaction constant can be quantified. Remarkably, its value can be as high as the interfacial DMI constant for thin films and can be tuned by the parabola's curvature.

Curvilinear magnetic objects are in the focus of intensive research due to the possibility to obtain new fundamental effects and stabilize topologically non-trivial magnetic textures at the nanoscale [1]. The physics in these systems is driven by the interplay between exchange and magnetostatic interactions, which contain spatial derivatives in their energy functionals. This makes both interactions sensitive to the appearance of bends and twists in the physical space. Here, we address experimentally and theoretically curvature-induced effects in parabolic nanostripes with different geometrical parameters [2]. We show that two different magnetic states can appear: the homogeneous magnetic distribution along the parabolic stripe and a state with a transversal domain wall pinned at the vertex of the parabola. The analytical calculation, based on local magnetostatic model, showed its validity and applicability in a wide range of geometrical parameters. [1] R. Streubel et al., J. Phys. D: Applied Physics 49, 363001 (2016). [2] O. Volkov et al., Physica Status Solidi – Rapid Research Letters, 1800309 (2018).

A flexible bismuth-based Hall sensor is realized with a total thickness of only 80 $\mu $ m including encapsulation. After wiring, the sensors have a maximum height of 280 $\mu $ m and could be mounted onto curved surfaces with radii down to 5 mm without degradation of its performance. These flexible sensors allow one to measure time-varying magnetic fields and are applied to realize flux-based control strategies for magnetically suspended systems, which is demonstrated by means of a single-axis magnetic levitation setup.

A lab-on-chip device is demonstrated for probing the electrochemical kinetics, electrical properties, and structure integrity of a single Si rolled-up tube as the anode in lithium-ion batteries. Cyclic voltammetry of the tube exhibits better-resolved peaks than of the planar film due to the enhanced diffusion. The tube is wrinkled after cycling. The tube could be used as a promising ultra-microelectrode for other voltammetry research.

We investigate the iron-based superconductor Ba(Fe 1−x Co x ) 2As 2 (Ba-122) regarding its superconducting properties and possible applications. Therefore, Ba-122 thin films are used as base electrode to prepare different kinds of hybrid Josephson junctions with a counter electrode of the conventional superconductor Pb. Additionally, we use both c-axis and a b-plane transport geometries and different kinds of barriers like interface-engineered surfaces, sputtered titanium oxide and gold layers. Temperature dependent I– V characteristics as well as magnetic field dependence and microwave response of the junctions are shown. The examined I– V characteristics and I c R n– T behaviours of each junction type are compared and described according to the electrical behaviour of the respective normal conducting or insulating barrier. While the I c R n product of the interface-engineered barrier junction was 12 μV and the planar junction with Au barrier showed 18 μV, we could increase the I c R n to 90 μV for planar TiO x barrier junctions.

The Hall effect is a powerful tool for investigating carrier type and density. For single-band materials, the Hall coefficient is traditionally expressed simply by $R_H^{-1} = -en$, where $e$ is the charge of the carrier, and $n$ is the concentration. However, it is well known that in the critical region near a quantum phase transition, as it was demonstrated for cuprates and heavy fermions, the Hall coefficient exhibits strong temperature and doping dependencies, which can not be described by such a simple expression, and the interpretation of the Hall coefficient for Fe-based superconductors is also problematic. Here, we investigate thin films of Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ with compressive and tensile in-plane strain in a wide range of Co doping. Such in-plane strain changes the band structure of the compounds, resulting in various shifts of the whole phase diagram as a function of Co doping. We show that the resultant phase diagrams for different strain states can be mapped onto a single phase diagram with the Hall number. This universal plot is attributed to the critical fluctuations in multiband systems near the antiferromagnetic transition, which may suggest a direct link between magnetic and superconducting properties in the BaFe$_2$As$_2$ system., Comment: Accepted for publication in Scientific Reports, 6 main figures plus Supplemental Information (8 figures)

Electrochemical deposition in alumina templates is proved as a promising method for production of Co(Cu)/Cu nanowires showing high giant magnetoresistance (GMR). This study discusses the deposition of multilayered structures in highly ordered alumina templates in dependence on diffusion (Cu) or kinetically controlled (Co) behavior. Results show a high impact of spherical diffusion on the enhancement of current density of the diffusion controlled component compared to deposition of thin films on planar electrodes. To achieve a separation of the layers and to decrease the amount of Cu in the Co layer the deposition potential of Co was shifted toward more negative potentials. Lithographic structuring of the template surface was carried out to allow a 4-point measurement of the resistance. A high GMR of about 12% was obtained for [Co(Cu) (9 nm)/Cu (11 nm)](380) multilayered nanowires with high accuracy and reproducibility. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.006302jes] All rights reserved.

In the living cell, proteins are able to organize space much larger than their dimensions. In return, changes of intracellular space can influence biochemical reactions, allowing cells to sense their size and shape. Despite the possibility to reconstitute protein self-organization with only a few purified components, we still lack knowledge of how geometrical boundaries affect spatiotemporal protein patterns. Following a minimal systems approach, we used purified proteins and photolithographically patterned membranes to study the influence of spatial confinement on the self-organization of the Min system, a spatial regulator of bacterial cytokinesis, in vitro. We found that the emerging protein pattern responds even to the lateral, two-dimensional geometry of the membrane such that, as in the three-dimensional cell, Min protein waves travel along the longest axis of the membrane patch. This shows that for spatial sensing the Min system does not need to be enclosed in a three-dimensional compartment. Using a computational model we quantitatively analyzed our experimental findings and identified persistent binding of MinE to the membrane as requirement for the Min system to sense geometry. Our results give insight into the interplay between geometrical confinement and biochemical patterns emerging from a nonlinear reaction–diffusion system.

Bismuth thin films were grown on oxidized Si substrates by electron beam evaporation. The films showed clear tendency to form hillocks inducing large surface roughness. The evolution of hillocks with film thickness and deposition rate was studied. In order to improve the surface quality of the Bi films a nanoscale mechanical polishing was performed. Upon polishing. hillocks-free Bi thin films were obtained without influencing the crystalline structure and the resistivity of the films. The achieved film surface quality allows to prepare high quality Bi Hall probes with an active area down to the nm(2) range promising for advanced device performance. (C) 2012 Elsevier B.V. All rights reserved.

We fabricated self-powered colloidal Janus motors combining catalytic and magnetic cap structures, and demonstrated their performance for manipulation (uploading, transportation, delivery) and sorting of microobjects on microfluidic chips. The specific magnetic properties of the Janus motors are provided by ultrathin multilayer films that are designed to align the magnetic moment along the main symmetry axis of the cap. This unique property allows a deterministic motion of the Janus particles at a large scale when guided in an external magnetic field. The observed directional control of the motion combined with extensive functionality of the colloidal Janus motors conceptually opens a straightforward route for targeted delivery of species, which are relevant in the field of chemistry, biology, and medicine.

The dynamic magnetic properties of soft-ferromagnetic thin film element arrays are strongly influenced by long range interelement magnetostatic interaction. In order to estimate the effective array dipolar field a quantitative model is presented, which is based on the superposition of stray fields that arise from the neighborhood of a reference element. Kittel's equation, that describes the magnetodynamics, is generalized for magnetically saturated arrays by additional array dipolar field terms. Measurements of the magnetodynamic response of quasi-saturated arrays with a rectangular base agree with theoretical predictions. Thus, our model allows the estimation of the frequency of the uniform precessional mode in mesoscopic thin film arrays with non-negligible magnetostatic interaction.

Magnetic vortices show promise as data storage structures, however the vortex formation process imposes a lower limit on the element’s size. In this article a technique is presented, which application increases the probability of nucleating of magnetic vortices in sub-micrometer sized soft magnetic thin film elements. By tailoring the edge geometry of the elements, the symmetry of their magnetic configuration is broken in a manner which favors vortex nucleation. Micromagnetic simulations are presented, which demonstrate this effect in soft-magnetic disks with beveled edges. The favored edge geometry is realized by applying nanosphere lithography directly on top of a ferromagnetic thin film material. In this process, the film is masked with a self assembled monolayer of SiO2-nanospheres and subsequently ion-etched. The resulting magnetic reversal loops show that in both magnetically isolated as well as in closely packed arrays of beveled disks, vortex formation takes place. The technique presented facilitates the vortex formation even in closely packed and small elements. The lowering of the minimum critical diameter for vortex formation enables a significant increase of data storage density in devices based on magnetic vortices.

We investigate the relaxation of rectangular wrinkled thin films intrinsically containing an initial strain gradient. A preferential rolling direction, depending on wrinkle geometry and strain gradient, is theoretically predicted and experimentally verified. In contrast to typical rolled-up nanomembranes, which bend perpendicular to the longer edge of rectangular patterns, we find a regime where rolling parallel to the long edge of the wrinkled film is favorable. A non-uniform radius of the rolled-up film is well reproduced by elasticity theory and simulations of the film relaxation using a finite element method., 4 pages, 4 figures

Bismuth Hall probes with an active area in the µm2 and sub-µm2 (down to (100 × 100) nm2) range have been fabricated on SiO2/Si substrates. The structural and electrical properties of Bi films with a thickness of 20–90 nm were investigated. Critical values of the structural characteristics, at which the film resistivity dependences undergo a distinct change were found. The transition to low resistivity, good crystallinity and high degree of texturing were observed at a film thickness of 65 nm. The potential use of the Bi Hall sensor as a swell sensor for monitoring the swelling of stimuli-sensitive hydrogels was demonstrated.

This paper reports the observation of giant persistent photoconductivity from rough Si nanomembranes. When exposed to light, the current in p-type Si nanomembranes is enhanced by roughly 3 orders of magnitude in comparison with that in the dark and can persist for days at a high conductive state after the light is switched off. An applied gate voltage can tune the persistent photocurrent and accelerate the response to light. By analyzing the band structure of the devices and the surfaces through various coatings, we attribute the observed effect to hole-localized regions in Si nanomembranes due to the rough surfaces, where light can activate the confined holes.

Flexible electronics, extremely sensitive sensors, strained-silicon technology, andmacromolecule separation, are only a few examples stimulating increasing interest in free-standing nanomembranes, which can be fabricated out of thin solid films, particle nanocomposites, organic layers, organic/inorganic networks, and even graphene sheets. Strain engineering offers an advanced strategy to deterministically rearrange such nanomembranes into threedimensional micro-/nanostructures including tubes, helices, rings, wrinkles and other advanced microarchitectures, all of which serve for applications in electronics, mechanics, fluidics, and photonics. The fabrication often requires a selective underetching procedure to release the nanomembranes from their substrate, which heavily constraints the number of desirable materials for exciting applications in, e.g., metamaterials or biomedical research. The material choice is limited, because the selective underetching not only removes the underlying sacrificial layer but also in many cases dissolves the nanomembrane material itself. We circumvent this problem for a broad range of materials and material combinations by a new approach outlined in Figure 1a. A pre-stressed inorganic nanomembrane deposited at low temperatures onto a polymer sacrificial layer (here: photoresist) is released from the substrate surface by removing

DNA molecules in silicon dioxide-glass fluidic nanoslits spontaneously extend at the lateral sidewalls of the slit. The nanoslit geometry, however, physically confines polymer molecules to two spatial dimensions; further reduction in configurational entropy resulting in axially stretched molecules arises spontaneously and appears to be electrostatically mediated. The observations not only shed light on electrostatic interactions of charged soft matter with like-charged confining walls but also offer a new method to stretch DNA in solution.

Vertically aligned Fe-filled multi-wall carbon nanotubes (MWNTs) have been grown selectively on the SiO2 surfaces of patterned amorphous carbon (a-C)/SiO2/Si substrates. Their morphology, structure and magnetic properties have been studied. The a-C patterns were prepared using conventional lithography processes combined with a sputter-deposition of a-C (thickness of 100 nm). The aligned Fe-filled MWNTs were produced by pyrolysis of ferrocene in a CVD reactor with a two zone furnace system and have high filling yield. The encapsulated Fe nanowires grown on the SiO2 structures of the patterned a-C/SiO2/Si substrates have diameters of 10-20 nm and can reach a few micrometers in length. The described method enables the preparation of complex architectures of Fe-filled MWNTs and may be used for future applications based on filled nanotubes.

Arrays of vertically aligned Fe‐filled multi‐wall carbon nanotubes (MWNTs) on oxidized silicon substrates were prepared by pyrolysis of ferrocene in a dual furnace system and characterized by electron microscopy and magnetometry measurement. The effect of the growth temperature on both the filled nanotube morphology and their magnetic behavior was studied. Increasing the growth temperature in the range of 845–1035°C the nanotube alignment becomes worse and the diameter of the encapsulated Fe nanowires increases from 10 to 40 nm. Both the coercivity and the remanence ratio of the arrays of Fe‐filled MWNTs decrease with the increase of the growth temperature. Factors causing the observed magnetic behavior are discussed.

Fe‐filled multi‐wall carbon nanotubes (MWNTs) were produced by pyrolysis of ferrocene in a dual furnace system. They grew vertically aligned on oxidized silicon substrates placed inside the reaction zone of a chemical vapor deposition reactor. A variation of the growth parameters has been performed in order to evaluate the possibility to control the Fe‐filled nanotube growth process and thereby the nanotube‐ and the filling length, diameter and yield, and also the nanotube alignment. Electron microscopy studies show nanotubes with quite different morphologies. The relation between the aligned Fe‐filled MWNTs growth and the most important growth parameters is discussed.

Highly flexible bismuth Hall sensors on polymeric foils are fabricated, and the key optimization steps that are required to boost their sensitivity to the bulk value are identified. The sensor can be bent around the wrist or positioned on the finger to realize an interactive pointing device for wearable electronics. Furthermore, this technology is of great interest for the rapidly developing market of -eMobility, for optimization of eMotors and magnetic bearings.

The flourishing and eagerness of portable consumer electronics necessitates functional elements to be lightweight, flexible, and even wearable (Figure 1) [1], fulfilling the needs of soft robotics, medical implants, imperceptible and transient electronics [2-4]. Next generation flexible appliances aim to become fully autonomous and will require ultra-thin and flexible navigation modules, body tracking and relative position monitoring systems. Key building blocks of navigation and position tracking devices are the magnetic field sensors.

The work addresses the correlation between the phase composition and the magnetic characteristics of aligned Fe-filled multi-walled carbon nanotubes (Fe-MWCNTs) grown by pyrolysis of ferrocene on oxidized Si substrates. In a combinatorial approach we exploited the extremely high gradients of the technological parameters temperature and ferrocene flow across the surface of a substrate positioned close to the reactor wall to obtain a large variation in the structural and magnetic properties of the Fe-MWCNTs. In this way, we established several clear correlations between the Fe-filling phase composition and the overall magnetic characteristics of the aligned Fe-MWCNTs. The α-Fe rich samples, which possess a more ordered graphitic sheet structure, a higher degree of preferred crystalline orientation of the metal filling and much larger metal crystallites in comparison with the carbide-rich samples, show a much stronger magnetic anisotropy with easy axis perpendicular to the substrate and unusually high values of the coercive field H c and the saturation field H s . The changes in the measured saturation magnetisation M s and the H c values correlate well with the variation of the α-Fe content and the filling crystallinity. A special annealing treatment of the samples causes a distinct increase of the α-Fe quantity and an increase of the measured average grain size. The respective magnetic characteristics show a significant increase of the overall magnetic moment and decrease of the coercive field. The correlation between the structural and the magnetic characteristics of the annealed samples matches quite well the respective correlations in the case of as-deposited samples.

Cross-linking of water-soluble polymers by high-energy irradiation provides a clean method for the synthesis of hydrogels. Some applications of stimuli-sensitive polymers need different patterns in the micro- and submicrometet range on a supporting material. A dry layer of poly(vinyl methyl, ether) on a Si-wafer was cross-linked and patterned by irradiation with the electron beam of a modified electron microscope. The patterns in the micro- and submicrometer range show good adhesion on the supporting material without adhesion promoter. The deformation and the elastic behavior of the pattern were tested by AFM. The formed gel structures were sensitive against changes in environmental condition. This offers a wide range of applications.

Aligned Fe–Co alloy–filled multi-walled carbon nanotubes (MWNTs) were synthesized on silicon substrates via the pyrolysis of a ferrocene/cobaltocene mixture. The nanotubes are aligned normal to the substrate surface. The encapsulated metal nanowires have diameters of 10–20 nm and a length of up to a few micrometers. They consist of single crystals with BCC structure. Alternating gradient magnetometry investigations show that the magnetic wires exhibit a clear ferromagnetic behavior at room temperature. An enhanced coercivity of about 126 mT and uniaxial magnetic anisotropy with the easy axis of magnetization along the wire axis were observed.

AlOx tunnel barriers prepared by oxidizing ultra-thin Al films of various thickness by means of a Rf wave resonance plasma beam source were investigated to understand the influence of the plasma oxidation conditions on the junction resistance Rj, the magnetoresistance ratio (MR) and the switching characteristics of exchange-biased magnetic tunnel junctions (MTJs) with NiMn pinning layer. The junction properties were characterized as a function of oxidation time, plasma power and distance between plasma source and sample. The MR of the as-deposited junction was about 15%. The highest exchange bias fields (17 mT) and pinned layer coercivities (23 mT) can be achieved with extended annealing at low temperatures T ≅ 32 0 ∘ C or with a rapid annealing at T ≅ 40 0 ∘ C , respectively. Short-time annealing (1 min) at intermediate temperatures (350 °C) and field cooling at 1 T leads to the highest MR effect of 35% at room temperature and 55% at 4.2 K.

We report on a method for the selective growth of aligned cobalt (Co)‐filled multi‐walled carbon nanotubes (MWNTs) using the pyrolysis of cobaltocene. The nanotubes grow preferentially on Fe structures patterned onto SiO2/Si substrates by a lift‐off process. The filling is discontinuous and forms a sequence of nanowire segments located along the tube. The nanowires consist of single crystalline grains with fcc structure. They have diameters of 10–20 nm and their length reaches several hundred nanometers. Our method allows the building of a system of oriented MWNTs filled with ferromagnets. It may be applied for fabricating nanotube‐based microelectronic devices.

We present results for magnetotransport measurements on multiwall-carbon nanotubes (MWCNT) contacted by cobalt electrodes. By measuring the V(I) characteristics at constant magnetic fields and different orientation of the magnetization directions in the Co electrodes, we were able to determine both current and voltage dependences of the magnetoresistance (MR) effects. These tunneling MR values are compared with the directly measured MR at constant current with sweeping magnetic field. The V(I) curves show an ohmic behavior at 295 K and a non-linear tunneling behavior at 4.2 K. With decreasing bias current the MR increased up to 60% at 4.2 K, and with decreasing bias voltages even up to 175%. The MR disappears at high bias current (voltages) and temperatures higher than 40 K. For most of the samples the current dependences of the MR were found to be nearly symmetric upon reversing the current direction. However, in some cases we also observed a sign change of the MR as function of the applied current, which suggests an inversion of the spin polarization in one of the Co interfaces.

Carpet-like flakes (area < 9 mm 2 ; thickness < 50 μm) of well-aligned Co-filled multi-walled carbon nanotubes were grown by decomposition of cobaltocene. The nanotubes have outer diameters of 50-90 nm and a metal core of 15-30 nm diameter. They are discontinuously filled with f.c.c.-Co nanowires of up to a few micrometers in length. Magnetometry studies show a weak uniaxial magnetic anisotropy with the easy axis along the nanowires and a high coercivity of about 59 mT. Electron holography provides information about the magnetic characteristics of individual nanowires.

Single- and multi-walled carbon nanotubes are very interesting nanoscaled materials with many possible applications in nanoelectronics. Especially, nanotubes filled with ferromagnetic materials (Fe, Co, Ni) may have significant potential in data storage. Such structures may help to exceed the best available storage densities (>65 Gb/inch2) and show in the case of Fe-filled nanotubes higher coercivities compared to bulk Fe. In addition, metal-filled carbon nanotubes are promising nanowires with excellent oxidation protection. In this paper we describe the synthesis of Fe-, Ni- and Co-filled carbon nanotubes by using the chemical vapor deposition method. Varying the deposition conditions we have obtained filled nanotubes with relatively uniform core diameters and different thicknesses of the carbon walls. The core diameters vary between 15 and 30 nm and the thickness of the carbon shells between 2 and 60 nm. The length of the tubes amounts up to 30 μm. The filled carbon nanotubes are characterised by scanning and transmission electron microscopy and energy dispersive X-ray analysis. The magnetic behaviour of the aligned Fe-filled tubes is investigated using alternating gradient magnetometry measurements and electron holography. The hysteresis loops indicate a magnetic anisotropy. The coercivity depends on the direction of the applied magnetic field. The observed enhanced coercivities are significantly higher than in bulk Fe.

We have studied the effect of the dipolar magnetic coupling (also known as Neel coupling or “orange-peel” coupling) in tunneling magnetoresistive (TMR) elements. With an in situ scanning tunneling microscope we directly accessed the roughness of the films and found a close correspondence between the values for the coupling fields determined by the magneto-optical Kerr effect and the ones computed on the basis of the measured morphology parameters. We confirm an increase of the dipole coupling between the magnetic layers with decreasing barrier thickness as predicted by the model. Deviations from the theoretical predictions are observed for the case of thinner soft magnetic layers, which can be explained by reduced magnetization in very thin films. We demonstrate the importance of dipolar coupling for understanding the magnetic behavior of TMR elements by comparing TMR curves for optimized and nonoptimized structures.

In the presented work the controlled mechanical modification of conducting lines on a nanometer scale by a scanning force microscope will be demonstrated. To achieve the high loads necessary for the modification of the lines, noncontact cantilevers and home made supertips have been used in contact mode. Aluminium and an alloy of gold-palladium have been used as materials for studying the influence of the different parameter as well as the mechanical properties of the thin films on the modification process. Qualitative conclusions will be made. The process of modification is monitored and controlled for the first time by an in situ measurement of the electric resistance of the modified conducting line. A Wheatstone bridge and lock-in technique have been used to observe the change in the resistance. (C) 1997 Elsevier Science Ltd.

We describe the synthesis and the properties of Fe-filled multi-walled carbon nanotubes (MWNTs) and nanoparticles (NP) produced by chemical vapor deposition (CVD). We have employed ferrocene as a starting substance and oxidized Si-wafers as substrates. The magnetic properties and the interaction of the material with bladder cancer cells were determined. After the addition of NP suspensions to cultured cells, no adhesion of the nanoparticles/nanotubes (NT/NP) to the cell membrane and also no cellular uptake were observed. However, the preincubation of the (NT/NP) suspension with cationic lipid caused an efficient delivery of the lipid-nanostructure complexes into the cytoplasm within 2 h after adding to the culture medium.

We present recent results of time-resolved x-ray photoemission electron microscopy on permalloy microstructures. The stroboscopic experiments feature a time-resolution of Deltatauless than or equal to130 ps. We observe a strong influence of incoherent magnetization rotation processes, leading to a significant transient stray-field formation at the edges of the microstructure. (C) American Institute of Physics.

Monomolecular resist films of tricosanoic acid prepared on top of thin Au- and Pt-films by the Langmuir-Blodgett technique have been exposed by high and low voltage electron beams. Up to now patterns have been obtained with a line width down to about 100 nm. For a 10-monolayer resist successful pattern transfer into an 80 nm Au-film has been demonstrated.

Monomolecular resist films of tricosenoic and tricosenoic acid as well as polymethylmethacrylate (PMMA), prepared on thin Au and PT films by the Langmuir-Blodgett (LB) technique have been exposed by electron-beams with an energy down to 2 keV. Below 5 keV, PMMA was found to act either as positive or negative resist depending on the dose. Ultra low voltage beam (less than or equal to 10 V) experiments with the scanning tunnelling microscope (STM) have not yet resulted in polymerization of the films. Pattern transfer into the Au films by wet or Ar ion etching has been demonstrated.

We report on the magnetic properties of Fe-filled multiwalled carbon nanotubes (MWNTs) grown by chemical vapor deposition (CVD) on Si substrates with ferrocene as precursor. The MWNTs are aligned perpendicularly to the substrate plane. X-ray diffraction analyses indicate the presence of both bcc and fcc iron with a relatively strong texture. Magnetometry measurements show a pronounced magnetic anisotropy with the easy axis perpendicular to the substrate plane and parallel to the axis of the aligned MWNTs, respectively. The low-temperature behavior suggests a negligible coupling between the two iron phases. We accessed the magnetic properties of individual Fe-filled MWNTs by electron holography using a transmission electron microscope (TEM).

We describe the preparation and the properties of Fe-filled multi-walled carbon nanotubes on Co-coated oxidized silicon substrates. The material was grown by pyrolysis of ferrocene, using a chemical vapor deposition process. Scanning and transmission electron microscopy studies indicate that the material consists of filled and aligned MWNTs. They have outer diameters of 40–100 nm and diameters of the metal core of 20–40 nm. Energy dispersive X-ray analysis of individual tubes reveals that their filling consists of pure Fe. Alternating gradient magnetometry investigations demonstrate the ferromagnetic behavior of the filled tubes. We observe unique magnetic properties differing from those of bulk Fe.

The magnetodynamics of lens-shaped thin-film elements are studied using vector network analyzer ferromagnetic resonance. A strong increase in the frequency at resonance is found when approaching the switching field. From magnetic force microscopy imaging the increase in resonance frequency is ascribed to the formation and evolution of a buckling domain state. The experimental data are qualitatively reproduced by micromagnetic simulations of a model element. Thereby, the roles of the external magnetic field and the buckling wavelength are extracted separately. Magnetic domain modes with dynamic magnetization modulations parallel and perpendicular to the static magnetization are identified. Based on magnetostatic energy considerations qualitative arguments are derived that allow for an interpretation of the dynamic response in such low-symmetry magnetization distributions.

Magnetotransport of individual rolled-up Fe(3)Si nanomembranes is investigated in a broad temperature range from 4.2 K up to 300 K in pulsed magnetic fields up to 55 T. The observed magnetoresistance (MR) has the following pronounced features: (i) MR is negative in the investigated intervals of temperature and magnetic field; (ii) its magnitude increases linearly with the magnetic field in a low-field region and reveals a gradual trend to saturation when the magnetic field increases; (iii) the MR effect becomes more pronounced with increasing temperature. These dependences of MR on the magnetic field and temperature are in line with predictions of the spin-disorder model of the spin-flip s-d interaction assisted with creation or annihilation of magnons, which is expected above a certain critical temperature. Comparison of the MR features in rolled-up and planar samples reveals a substantial increase of the critical temperature in the rolled-up tube, which is attributed to a new geometry and internal strain arising in the rolled-up nanomembranes, influencing the electronic and magnetic properties of the material.

We report on both the global and micromagnetic properties of interlayer exchange coupled spin systems. Irradiation with Ne ions is employed to achieve a phase transition from antiferromagnetic to ferromagnetic coupling. For extended trilayer films a full quantitative analysis of the bilinear and biquadratic coupling constants is performed. With increasing ion fluence we observe a steady increase of the bilinear coupling constant at an almost negligible decrease in saturation magnetization. The mixing of atoms at the layer interfaces is identified as the origin for this. The effects of ion modification on the magnetic microstructure are studied for the model system of layered vortex pairs. X-ray microscopy is used to directly image the individual magnetization circulations in trilayer disks. The circulation configuration is found to be determined by the film coupling for both coupling orientations with a homogenous coupling angle throughout the structure. For the vortex cores however, micromagnetic simulations indicate that due to the significant local demagnetization fields the parallel states are always energetically preferred. Nevertheless antiparallel configurations are metastable, having their signature in reduced core diameters. Our study provides new results on spin structures in interlayer exchange coupled trilayers and it demonstrates a promising way to control the local interlayer coupling post-deposition.

The spin-coherent quantum transport through multiwall carbon nanotubes contacted by ferromagnetic Co pads is investigated experimentally. At 4.2 K, the devices show a remarkable increase of the magnetoresistance (MR) ratio with decreasing junction bias, reaching a maximum MR ratio of 30% at a junction bias current of 1 nA. The experimental results suggest the transport to be dominated by spin-dependent tunneling processes at the Co/nanotube interfaces and governed by the local magnetization. We also observe an asymmetry of the magnetoresistance peak position and width which is attributed to a local exchange biasing in the electrode material.