In this work we demonstrate a spin-orbit torque (SOT) magnetic field sensor, designed as a Ta/CoFeB/MgO structure, with high sensitivity and capable of active offset compensation in all three spatial directions. This is described and verified in both experiment and simulation. The measurements of magnetic fields showed an offset of 36, 50, and 37μT for x-, y-, and z-fields. Furthermore, the sensitivities of these measurements had values of 590, 580, and 490V A^-1 T^-1 in the x-, y-, and z-direction. In addition, the robustness to bias fields is demonstrated via experiments and single spin simulations by applying bias fields in y-direction. Cross sensitivities were further analyzed via single spin simulations performing a parameter sweep of different bias fields in the y- and z-direction up to ±1mT. Finally, the extraction of the SOT parameters η_DL and η_FL is shown via optimization of a single-spin curve to the experimental measurements.

Rolling element bearing faults significantly contribute to overall machine failures, which demand different strategies for condition monitoring and failure detection. Recent advancements in machine learning even further expedite the quest to improve accuracy in fault detection for economic purposes by minimizing scheduled maintenance. Challenging tasks, such as the gathering of high quality data to explicitly train an algorithm, still persist and are limited in terms of the availability of historical data. In addition, failure data from measurements are typically valid only for the particular machinery components and their settings. In this study, 3D multi-body simulations of a roller bearing with different faults have been conducted to create a variety of synthetic training data for a deep learning convolutional neural network (CNN) and, hence, to address these challenges. The vibration data from the simulation are superimposed with noise collected from the measurement of a healthy bearing and are subsequently converted into a 2D image via wavelet transformation before being fed into the CNN for training. Measurements of damaged bearings are used to validate the algorithm's performance.

Magnetoresistive sensors based on giant magnetoresistance (GMR) or tunnel magnetoresistance (TMR) play a major role towards the miniaturization in the industrial society. Typically, spin-valve-type magnetoresistive sensors are embedded in a Wheatstone bridge configuration with rectangular, meander-like or elliptically shaped thin film elements. Such elements usually switch via multi-domain, C- or S-shaped magnetization states and, therefore, often exhibit an open non-linear hysteresis curve. Linearity and hysteretic effects are key features in the improvement of such sensors. We will present a different approach by using circularly shaped elements exhibiting a different magnetization state of a magnetic vortex [1]. This is one of the fundamental magnetization ground states occurring in disk-shaped thin film elements and is characterized by minimization of the demagnetizing energy at the expense of exchange energy. Experimental data were generated on electrically contacted GMR and TMR disks which were fabricated by optical lithography. The following advantages will be discussed and compared to standard elliptical sensor elements. (a) The vortex state shows essentially no hysteresis in the minor loop. (b) Since the vortex nucleation happens prior to the zero field, the M(H=0)=0 crossing is independent of history. (c) The critical fields can be easily controlled by the element geometry. (d) The noise is low. All characteristic experimental values have been determined in dependence of free layer thickness, disk diameter and temperature. These findings are discussed in the frame of the semi-analytical rigid-vortex-model [2] and micromagnetic simulations. The financial support by the Austrian Federal Ministry of Science, Research and Economy and the Christian Doppler Research Association in Austria is gratefully acknowledged. [1] D. Suess, A. Bachleitner-Hofmann, A. Satz, H. Weitensfelder, C. Vogler, F. Bruckner, C. Abert, K. Prügl, J. Zimmer, C. Huber, S. Luber, W. Raberg, T. Schrefl, H. Brückl, „Topologically Protected Vortex Structures to Realize Low-Noise Magnetic Sensors with High Linear Range”, Nature Electronics 1, 362 (2018) [2] K. Y. Guslienko et al., “Magnetization reversal due to vortex nucleation, displacement, and annihilation in submicron ferromagnetic dot arrays”, Phys. Rev. B 65 (2001)

Micromagnetic sensors play a key role in a variety of industries, including the automotive industry, where they are used, for example, for speed and position detection. The adoption of emerging magnetoresistive sensor technology such as anisotropic magnetoresistance, giant magnetoresistance and tunnel magnetoresistance sensors is driven principally by their enhanced sensitivity and improved integration capabilities compared with conventional Hall effect sensors. At the heart of such sensors is a microstructured ferromagnetic thin-film element that transduces the magnetic signal, but these elements often exhibit a nonlinear hysteresis curve and the performance of the sensors is limited by magnetic noise. Here, we examine the origin of magnetic noise in magnetoresistive sensors and show that a topologically protected magnetic vortex state in the transducer element can be used to overcome these limitations. Using analytic and micromagnetic models, we find that the noise is due mainly to irreproducible magnetic switching of the transducer element at external fields that are close to the Stoner–Wohlfarth switching field. Then, using a flux-closed vortex configuration, we develop a giant magnetoresistance sensor layout that, compared to existing state-of-the-art sensors, has lower magnetic noise, a linear regime that is around an order of magnitude higher and negligible hysteresis.

Non-uniform current distributions of spin valves with disk shaped free layers are investigated. In the context of spin valves, the vortex state, which is the ground-state in many disk shaped magnetic bodies, allows for distinct parallel channels of high and low resistivity. The readout current is thus able to evade high resistivity regions in favor of low resistivity regions, giving rise to 'conductive inhomogeneities'. Therefore, the total resistance of the spin valve does not always correspond exactly to the total average magnetization of the free layer. In addition, the resistance transfer function can be significantly influenced by the spatial placement of the electrodes, giving rise to 'geometric inhomogeneities'. The resulting deviations from resistance to magnetization transfer function are investigated for different spin valve geometries and compared to measurements of comparable devices.

Micromagnetic sensors play a major role towards the miniaturization in the industrial society. The adoption of new and emerging sensor technologies like anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR) and tunnel magnetoresistance (TMR) sensors are mainly driven by their integrability and enhanced sensitivity. At the core of such sensors, a microstructured ferromagnetic thin film element transduces the magnetic signal. Such elements usually switch via multi-domain, C- or S-shaped magnetization states and, therefore, often exhibit an open non-linear hysteresis curve. Linearity and hysteretic effects, as well as magnetic noise are key features in the improvement of such sensors. Here, we report on the physical origin of these disturbing factors and the inherent connection of noise and hysteresis. Critical noise sources are identified by means of analytic and micromagnetic models. The dominant noise source is due to irreproducible magnetic switching of the transducer element at external fields close to the Stoner Wohlfarth switching field. Furthermore, a solution is presented to overcome these limiting factors: a disruptive sensor design is proposed and analyzed which realizes a topologically protected magnetic vortex state in the transducer element. Compared to state of the art sensors the proposed sensor layout has negligible hysteresis, a linear regime about an order of magnitude higher and lower magnetic noise making the sensor ideal candidate for applications ranging from automotive industry to biological application.

Eggeling et al. (pp. 435–437) investigated the size and magnetic free layer dependence of the vortex dynamics in relatively large spin-valve nanocontacts. A circular nano- contact confines the current flow through a spin-valve multilayer (upper cover image) incorporating a magnetic free layer and an unpinned artificial antiferromagnet as polarizer. Spin-torque driven magnetic vortex dynamics are observed in dependence on the magnetic properties, the contact size and the applied current, provoking microwave oscillations at zero external magnetic field. The oscillation spectra (lower image) show the evolution of single and multiple radio frequency modes as a function of the nanocontact size. These specific properties make spin-torque-driven devices suitable e.g. for nano-sized microwave sources, ultra-compact magnetic field sensors or fast and non-volatile magnetic memories.

We report on the fabrication of polymer light-emitting diodes (PLEDs) and light-emitting electrochemical cells (LECs) in planar surface cell geometry (anode as well as the cathode are made of gold; interelectrode spacing: 1μm) by means of inkjet printing. The active material for PLEDs is an aqueous poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) dispersion, and for LECs blends thereof with poly(ethylene oxide) (two different molecular weights: 100,000g/mol (PEO-100,000) and 30,000g/mol (PEO-30,000)) and lithium-triflate, building the solid state electrolyte. The surface PLEDs reveal very poor device performance with extremely high current and light emission onset voltages. However, adding the solid state electrolyte to the luminescent material, leading to the device type of an LEC, distinctly improves the performance obtaining onset voltages slightly above 3V and remarkable enhanced light output. Due to the exchange of the high molecular weighted PEO-100,000 by the PEO-30,000, which leads to an elimination of the undesired bead-on-a-string effect during the inkjet printing process, the reproducibility of the device fabrication can be conspicuously improved. Additionally, the location of the light emission zone of a surface LEC can be easily determined, since one has a direct view between the electrodes. For such a device the light generation occurs near the cathode.

Microfabricated biochips are developed to continuously monitor cellular phenotype dynamics in a non-invasive manner. In the presented work we describe the novel combination of contact-less micro-dielectric sensors and microfluidics for quantitative cell analysis. The cell chip consists of a polymeric fluidic (PDMS) system bonded to a glass wafer containing the electrodes while temperature and fluid flow are controlled by external heating and pumping stations. Additionally, the cell chip contains an integrated reference arm providing a low-noise detection environment by eliminating background signals and interferences. The high-density interdigitated capacitors (µIDC) are designed to monitor living cells in a space of approximately 10 nL volume by controlling critical electrode characteristics, such as size, shape and passivation composition as well as thickness. The integrated µIDCs are isolated by a 300 nm multi-passivation layer of defined dielectric property and provide non-invasive, stable, robust and non-drifting measurement conditions. The performance of this detector is evaluated using various bacterial, yeast and mammalian cells.

Die Überwindung der beugungsbedingten Begrenzungen der konventionellen Mikroskopie gelingt durch die Tricks der ‚optischen Nahfeldmikroskopie’︁. Dabei wird die hohe Ortsauflösung der Rastertunnelmethoden mit der Vielfalt optischer Techniken kombiniert.

The re-magnetization process in a periodic magnetic stripe array has been studied for the easy axis configuration with a combination of direct and reciprocal space methods: Kerr microscopy and polarized neutron reflectivity. We investigated the magnetization reversal of a lateral array consisting of 80 nm Co0.7Fe0.3. The stripes are 2.4 µm wide with a grating period of 3 µm. Neutron scattering experiments were carried out at the ADAM reflectometer of the ILL. We discuss the case when a mag- netic field is applied parallel to the easy axis, i.e. parallel to the stripes and perpendicular to the scattering plane. In this field direction one can expect a classical re-magnetization sce- nario which implies homogeneous magnetization along the stripes until the coercive field Hc is reached and an almost simultaneous flip of the stripe magnetization into the field direction at Hc, as was observed for 1.2 µm wide stripes (1). Instead, a multi-domain structure was ob- served with Kerr microscopy already close to remanence, far below Hc, as shown in Fig.25(a). The contrast between neighboring domains is produced by magnetization directions, which are tilted away to the left and to the right relative to the net magnetization. At Hc (Fig.25(b)), the magnetization in some of the stripes suddenly alters its direction. The multi-domain state does also not disappear above Hc (Fig.25(c)). The Kerr microscopy images in Fig. 25 already give a good feeling about the general features of the magnetization arrangement over the stripes and on the size of the domains. However, they can hardly be used to obtain more quantitative information on the domain magnetic moment distribution and on correlations in their directions: the small domains in Fig. 25 are seen almost at the limit of resolution of this method. Neutron data, on the contrary, can deliver missing information, via the theoretical modelling of the experimental results. The multi-domain state manifests itself in the polarized neutron reflectivity measurements via basically two eects. The first one is a decrease of the mean magnetization of individual stripes, and this aects