Andrea Ehrmann

Andrea Ehrmann
Fachhochschule Bielefeld · Fachbereich Ingenieurwissenschaften und Mathematik

Prof. Dr. Dr. hab.

About

496
Publications
150,460
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3,348
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Introduction
Andrea Ehrmann currently works at the Fachbereich Ingenieurwissenschaften und Mathematik, Fachhochschule Bielefeld. Andrea does research in Textile Technologies, Didactics, Science Education and Engineering Physics. Her current projects are 'Projects along the textile chain', 'Nanomagnetism', and others.
Additional affiliations
June 2005 - February 2015
University Hochschule Niederrhein
Position
  • Scientific Staff

Publications

Publications (496)
Article
Highlights Magnetic single droplet and four-droplet spheres systems were examined with respect to their energy landscapes For thin oxide layers, the numbers of extrema are similar to spheres without coating For an oxide coated system, the maximum packing density is increased by 12%, as compared to the non-coated system Improved magnetic memory syst...
Article
Magnetic nanoparticles can be embedded in electrospun nanofibers and other polymeric matrices to prepare magnetic composites with defined magnetic and mechanical properties. Metal-oxide nanoparticles, such as magnetite or nickel-ferrite, are of special interest since they do not need a coating to avoid oxidation. Like other nanoparticles, these met...
Article
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While fused deposition modeling (FDM) and other relatively inexpensive 3D printing methods are nowadays used in many applications, the possible areas of using FDM-printed objects are still limited due to mechanical and thermal constraints. Applications for space, e.g., for microsatellites, are restricted by the usually insufficient heat resistance...
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--- Applied Research --- Graphical Abstract Phase change memory (PCM) belongs to the non-volatile solid-state memory techniques. Data are stored by setting each cell to a low-resistance (crystalline) or a high-resistance (amorphous) state. While fast switching and multi-level data storage are advantageous, writing currents and data retention still...
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- - - published in Technologies - - - Electrospinning is often investigated for biotechnological applications, such as tissue engineering and cell growth in general. In many cases, three-dimensional scaffolds would be advantageous to prepare tissues in a desired shape. Some studies thus investigated 3D-printed scaffolds decorated with electrospun...
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With a steadily increasing number of machines and devices producing electromagnetic radiation, especially, sensitive instruments as well as humans need to be shielded from electromagnetic interference (EMI). Since ideal shielding materials should be lightweight, flexible, drap-able, thin and inexpensive, textile fabrics belong to the often-investig...
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--- Textiles 2022, 2(2), 265-274 --- The electrocardiogram (ECG) is one of the most commonly measured biosignals. In particular, textile electrodes allow for the measuring of long-term ECG without skin irritation or other discomforts for the patient. Such textile electrodes, however, usually suffer from insufficient or unreliable skin contact. Thus...
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As the electron transport layer of dye-sensitized solar cells (DSSCs), the photoanode is an important component that affects photoelectric conversion efficiency (PCE). The commonly used material titanium dioxide (TiO2) is difficult to prepare as nanostructures with large specific surface area, which affects dye loading and electrolyte diffusion. He...
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Magnetic nanoparticles can be used for medical and other purposes, but can also be integrated in polymeric or other nonmagnetic matrices of diverse shapes, for example, thin-films or fibers. In the latter case, it may be important how the magnetic nanoparticles are distributed in the matrix, a topic which is often not taken into account when such c...
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Keratin is one of the most important protein materials and can act as a sustainable biopolymer for manifold applications. This paper reports on a sustainable extraction method for keratin from wool fiber materials. The use of this extracted keratin for polymer film preparation and preparation of nano-composite materials by electrospinning is invest...
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Atomic force microscopy (AFM) is one of the microscopic techniques with the highest lateral resolution. It can usually be applied in air or even in liquids, enabling the investigation of a broader range of samples than scanning electron microscopy (SEM), which is mostly performed in vacuum. Since it works by following the sample surface based on th...
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Long-term stability belongs to the main problems of dye-sensitized solar cells (DSSCs), impeding their practical application. Especially the usually fluid electrolyte tends to evaporation, thus drying the cells if they are not perfectly sealed. While gelling the electrolyte with different polymers often reduces the efficiency, using a glycerol-base...
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Stop marks are one of the most frequently occurring errors in warp-knitted fabrics. They become visible in a fabric each time a warp-knitting machine stops and restarts. Nevertheless, investigations of such stop marks are rarely found in scientific literature. Here, we report on time-dependent investigations of stop marks in warp-knitted fabrics. M...
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COMMUNICATIONS IN DEVELOPMENT AND ASSEMBLING OF TEXTILE PRODUCTS - - - - - Microalgae can be used for diverse applications in research and industry. Several microalgae grow adhering to surfaces that are usually two-dimensional. A third dimension could increase the amount of microalgae adhering to a given area and can be offered by textile fabrics....
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To measure biosignals constantly, using textile-integrated or even textile-based electrodes and miniaturized electronics, is ideal to provide maximum comfort for patients or athletes during monitoring. While in former times, this was usually solved by integrating specialized electronics into garments, either connected to a handheld computer or incl...
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Carbon nanofibers are used for a broad range of applications, from nano-composites to energy storage devices. They are typically produced from electrospun poly(acrylonitrile) nanofibers by thermal stabilization and carbonization. The nanofiber mats are usually placed freely movable in an oven, which leads to relaxation of internal stress within the...
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Electrospinning can be used to produce nanofiber mats containing diverse nanoparticles for various purposes. Magnetic nanoparticles, such as magnetite (Fe3O4), can be introduced to produce magnetic nanofiber mats, e.g., for hyperthermia applications, but also for basic research of diluted magnetic systems. As the number of nanoparticles increases,...
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3D printing is nowadays used for many applications far beyond pure rapid prototyping. As tools to prepare custom-made objects which may be highly complex, different 3D printing techniques have emerged into areas of application where the mechanical, thermal, optical and other properties have to meet high requirements. Amongst them, applications for...
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The emerging technology of 3D printing can not only be used for rapid prototyping, but will also play an important role in space exploration. Additive manufactured parts can be used in diverse space applications, such as magnetic shields, heat pipes, thrusters, etc. Three-dimensional printed parts offer reduced mass, high possible complexity, and f...
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- - - COMMUNICATIONS IN DEVELOPMENT AND ASSEMBLING OF TEXTILE PRODUCTS - - - While shape memory alloys (SMAs) and shape memory polymers (SMPs) can already be found in diverse applications, shape memory textiles are less often used. Nevertheless, they are regularly investigated. Typical ways to produce shape memory textiles (SMTs) are introducing sh...
Article
Asymmetric hysteresis loops can be found in exchange-bias systems in which a ferromagnet is exchange-coupled with an antiferromagnet. In purely ferromagnetic samples, such effects can occur due to undetected minor loops or thermal effects. While the exchange bias is long established in hard-disk read/write heads and diverse spintronics applications...
Article
Magnetic nanofibers can be used for data transport and storage, especially related to the emerging field of neuromorphic computing. Domain walls in bent nanofibers can nucleate, e.g., due to rotating local magnetic fields. Their propagation through bent nanofibers, however, depends on the bending direction in correlation to the rotational orientati...
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A growing population needs an expansion of agriculture to ensure a reliable supply of nutritious food. As a variable concept, vertical farming, becoming increasingly popular, can allow plant growth for local food production in the vertical sense on, e.g. facades in addition to the classical layered structure in buildings. As substrates, textile fab...
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Combining textile fabrics with 3D printing has been investigated intensively during the last years. Mostly, research concentrated on the adhesion between both partners of the composite or on the new freedom of design, enabled by combining these techniques. Here, we present examinations of the influence of elastic 3D printed patterns on the elongati...
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Magnetic force microscopy (MFM) belongs to the methods that enable spatially resolved magnetization measurements on common thin-film samples or magnetic nanostructures. The lateral resolution can be much higher than in Kerr microscopy, another spatially resolved magnetization imaging technique, but since MFM commonly necessitates positioning a cant...
Conference Paper
Magnetic nanofibers are of great interest for applications like data transport and storage as well as in basic research. Especially bent nanofibers, which can unambiguously be produced by electrospinning, show a broad spectrum of possible magnetization reversal processes, depending on bending radius, geometry, magnetic field orientation, etc. Besid...
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Cosmic radiation belongs to the challenges engineers have to deal with when further developing space travel. Besides the severe risks for humans due to high-energy particles or waves, the impact of cosmic radiation on electronics and diverse materials cannot be neglected, even in microsatellites or other unmanned spacecraft. Here, we explain the di...
Conference Paper
Der 3D-Druck bietet heutzutage ganz neue Möglichkeiten, Schüler(innen) und Student(inn)en an verschiedenste Wissensgebiete heranzuführen. Neben der Konstruktion, die mit einfachen Online-Programmen begonnen und zu komplizierten Formen fortgeführt werden kann, spielt hier vor allem die Materialwissenschaft eine wichtige Rolle. Die meisten preiswerte...
Conference Paper
Smart Textiles, auch als intelligente Textilien bezeichnet, bieten in der Schule sowie im Bachelorstudium neue Möglichkeiten, motorische Fähigkeiten mit Elektronik-Kenntnissen zu verbinden. Die meisten Smart Textiles gehören zu den E-Textiles, den elektronischen Textilien, die beispielsweise leitfähige Garne als Datenleiter enthalten oder leitfähig...
Article
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Poly(lactic acid) (PLA) is one of the most often used polymers in 3D printing based on the fused deposition modeling (FDM) method. On the other hand, PLA is also a shape memory polymer (SMP) with a relatively low glass transition temperature of ~60 °C, depending on the exact material composition. This enables, on the one hand, so-called 4D printing...
Conference Paper
Investigating seedling germination, plant growth and flowering in simulated microgravity conditions in a clinostat is not only of academic interest, but also a highly important issue for long-term space missions. Another factor influencing plant growth and flowering, from that point of view, is the earth magnetic field which cannot be switched off...
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--- published in Technologies --- Poly(lactic acid) (PLA) belongs to the 3D printable materials which show shape-memory properties, i.e., which can recover their original shape after a deformation if they are heated above the glass transition temperature. This makes PLA quite an interesting material for diverse applications, such as bumpers, safety...
Chapter
Electrospinning is a versatile method to produce nanofibers or nanofiber mats from diverse polymers or polymer blends. Including ceramic or metallic nanoparticles can even be used to create purely inorganic nanofibers for diverse applications. On the other hand, biocompatible and biodegradable polymers are of high interest especially for biomedical...
Article
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Biosignals often have to be detected in sports or for medical reasons. Typical biosignals are pulse and ECG (electrocardiogram), breathing, blood pressure, skin temperature, oxygen saturation, bioimpedance, etc. Typically, scientists attempt to measure these biosignals noninvasively, i.e., with electrodes or other sensors, detecting electric signal...
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- - -Published in Technologies 9, 63 (2021) - - - Myoelectric signals can be used to control prostheses or exoskeletons as well as robots, i.e., devices assisting the user or replacing a missing part of the body. A typical application of my-oelectric prostheses is the human hand. Here, the development of a low-cost myoelectric thumb is described,...
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Electrospun poly(acrylonitrile) (PAN) nanofibers are typical precursors of carbon nano-fibers. During stabilization and carbonization, however, the morphology of pristine PAN nano-fibers is not retained if the as-spun nanofiber mats are treated without an external mechanical force, since internal stress tends to relax, causing the whole mats to shr...
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Molecular magnets are a relatively new class of purely organic or metallo-organic materials, showing magnetism even without an external magnetic field. This interdisciplinary field between chemistry and physics has been gaining increased interest since the 1990s. While bulk molecular magnets are usually hard to build because of their molecular stru...
Article
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3D printing belongs to the emerging technologies of our time. Describing diverse specific techniques, 3D printing enables rapid production of individual objects and creating shapes that would not be produced with other techniques. One of the drawbacks of typical 3D printing processes, however, is the layered structure of the created parts. This is...
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This study analyzes the acceleration of the arms of a dual system of manipulators that aim to achieve the minimum distance by mimicking the process of approaching spacecraft that are trying to connect. The research was performed simultaneously on a real model and its digital equivalent, in accordance with the Digital Twin (DT) approach. The obtaine...
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In biotechnology, the field of cell cultivation is highly relevant. Cultivated cells can be used, for example, for the development of biopharmaceuticals and in tissue engineering. Commonly , mammalian cells are grown in bioreactors, T-flasks, well plates, etc., without a specific substrate. Nanofibrous mats, however, have been reported to promote c...
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Electrospinning can be used to prepare nanofiber mats from diverse polymers, polymer blends, or polymers doped with other materials. Amongst this broad range of usable materials, biopolymers play an important role in biotechnological, biomedical, and other applications. However, several of them are water-soluble, necessitating a crosslinking step a...
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MATERIALS PROCEEDINGS - - - Combining soft and hard magnetic materials is not only of technological importance in diverse spintronics elements, but also of high interest in basic research. Here, we report on different arrays combining iron and nickel, e.g., by embedding circular nanodots of one material in a matrix of the other. Micromagnetic simul...
Article
Round magnetic nano-dots belong to the frequently investigated magnetic nanostructures since they can often reverse magnetization via a vortex state which is characterized by low stray fields, making them useful for data storage applications. Nano-rings, with an open aperture in the middle, regularly show flux-closed vortex states without a vortex...
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COMMUNICATIONS IN DEVELOPMENT AND ASSEMBLING OF TEXTILE PRODUCTS - - - 3D printing on textile fabrics can be used to create composites with position-dependent mechanical, water-resistant, magnetic or other properties. An important prerequisite to use such composites technologically or for design purposes is a sufficient adhesion between both materi...
Cover Page
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Planar, rigid glass substrates support the formation of organic small-molecular semiconductor thin films with extended crystalline texture and distinct pleochroism (top in the cover picture), visible by cross-polarized microscopy. Woven, soaking electrospun nanofiber mat substrates disrupt the crystalline growth, leading to the formation of submicr...
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Planar, rigid glass substrates support the formation of organic small‐molecular semiconductor thin films with extended crystalline texture and distinct pleochroism (top in the cover picture), visible by cross‐polarized microscopy. Woven, soaking electrospun nanofiber mat substrates disrupt the crystalline growth, leading to the formation of submicr...
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Electrochemical devices convert chemical reactions into electrical energy or, vice versa, electricity into a chemical reaction. While batteries, fuel cells, supercapacitors, solar cells, and sensors belong to the galvanic cells based on the first reaction, electrolytic cells are based on the reversed process and used to decompose chemical compounds...
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Computers nowadays have different components for data storage and data processing, making data transfer between these units a bottleneck for computing speed. Therefore, so-called cognitive (or neuromorphic) computing approaches try combining both these tasks, as is done in the human brain, to make computing faster and less energy-consuming. One pos...
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Magnetic nanodots are of high interest for basic research due to their broad spectrum of possible magnetic states and magnetization reversal processes. Besides, they are of technological interest since they can be applied in magnetic data storage, especially if vortex states occur in closed dots or open rings. While producing such nanorings and nan...
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Square magnetic nanodots can show intentional or undesired shape modifications, resulting in superellipses with concave or convex edges. Some research groups also concentrated on experimentally investigating or simulating concave nano-superellipses, sometimes called magnetic astroids due to their similarity to the mathematical shape of an astroid....
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Recent advances in optoelectronics are often based on thin‐film organic semiconductors. Interesting organic semiconductors are given by squaraines, small molecules that show excitonic coupling with visible light and are thus suitable for applications in solar cells and light sensors. While such squaraine thin films have already been proven to be su...
Article
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Shape memory polymers (SMPs) are polymers which ''remember'' their original shape and can return to it after deformation, if an external stimulus-often an increased temperature-is applied. Some SMPs can be 3D printed, typically by fused deposition modeling (FDM). The most well-known SMP is poly(lactic acid), which belongs to the most often used mat...
Article
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- - - published in Technologies - - - Shape-memory polymers (SMPs) can be deformed, cooled down, keeping their new shape for a long time, and recovered into their original shape after being heated above the glass or melting temperature again. Some SMPs, such as poly(lactic acid) (PLA), can be 3D printed, enabling a combination of 3D-printed shapes...
Article
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Poly(lactic acid) is not only one of the most often used materials for 3D printing via fused deposition modeling (FDM), but also a shape-memory polymer. This means that objects printed from PLA can, to a certain extent, be deformed and regenerate their original shape automatically when they are heated to a moderate temperature of about 60-100 °C. I...
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- - - Published in: Mater. Proc. - - - Horizontally shifted and asymmetric hysteresis loops are often associated with exchange-biased samples, consisting of a ferromagnet exchange-coupled with an antiferromagnet. In purely ferromagnetic samples, such effects can occur due to undetected minor loops or thermal effects. Simulations of ferromagnetic n...
Article
Full-text available
Fused deposition modeling (FDM) is one of the most often-used technologies in additive manufacturing. Several materials are used with this technology, such as poly(lactic acid) (PLA), which is most commonly applied. The mechanical properties of 3D-printed parts depend on the process parameters. This is why, in this study, three-point bending tests...
Article
Full-text available
Horizontally shifted and asymmetric hysteresis loops are often associated with exchange-biased samples, consisting of a ferromagnet exchange coupled with an antiferromagnet. In purely ferromagnetic samples, such effects can occur due to undetected minor loops or thermal effects. Simulations of ferromagnetic nanostructures at zero temperature with s...
Article
Full-text available
Two-dimensional structures, either periodic or random, can be classified by diverse mathematical methods. Quantitative descriptions of such surfaces, however, are scarce since bijec-tive definitions must be found to measure unique dependency between described structures and the chosen quantitative parameters. To solve this problem, we use statistic...
Presentation
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Shape-memory properties of 3D printed PLA structures
Article
Electrospun nanofibers produced from magnetic materials form a magnetic network which may be used for neuromorphic computing and other novel applications. While the influence of bending radii on the magnetization reversal in such nanofibers was already discussed in the literature, the often occurring beads along the fibers have not yet been investi...
Article
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Electrospinning can be used to prepare nanofibers from various polymers and polymer blends. The adhesion of nanofibers to the substrates on which they are electrospun varies greatly with the substrate material and structure. In some cases, good adhesion is desired to produce sandwich structures by electrospinning one material directly onto another....
Article
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During electrospinning, the flying nanofibers can be attracted by conductive areas such as copper tape on a nonconductive substrate, especially in case of magnetic nanofibers. The question arises, however, whether the conductivity or any other physical properties of these areas are responsible for this effect. Here, electrospinning polyacrylonitril...
Article
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Vacuum casting of polyurethane (PUR) in silicone molds is used industrially for the production of prototypes and small series as well as in various noncommercial research areas. This includes the reproduction of archeological findings, biological samples or electronic devices. In this study, the authors investigate the molding accuracy of different...
Article
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3D printed objects are nowadays not only used in prototyping, but also in small-scale production down to lot-size 1. While different 3D printing techniques can be applied for this purpose, a large amount of products is prepared by the simple and inexpensive fused deposition modeling (FDM) technique, applying a polymer which is molten, pressed throu...
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While 3D printing was in former times mostly used for rapid prototyping, nowadays it is also used for rapid manufacturing. To overcome the problems of relatively low production speed and in several cases insufficient mechanical properties of 3D printed objects, 3D printing can be combined with larger-scale production processes, e.g. by directly pri...
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Vertical farming may solve the problem that in many regions of the world, more area would be necessary to produce food, than it is available. Especially in large cities and other densely crowded areas, vertical farming can provide an efficient and eco-friendly way to feed people. While indoor vertical farming plants are usually highly automatized,...
Article
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Square and round magnetic nano-dots of varying dimensions exhibit a large amount of possible magnetization reversal processes, from domain wall nucleation and propagation to multi-vortex states. Clustering such single nano-dots, however, may strongly modify these magnetization reversal processes due to the interactions between neighboring particles...
Article
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Combining clusters of magnetic materials with a matrix of other magnetic materials is very interesting for basic research because new, possibly technologically applicable magnetic properties or magnetization reversal processes may be found. Here we report on different arrays combining iron and nickel, for example, by surrounding circular nanodots o...
Article
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Polyacrylonitrile (PAN) nanofiber mats are typical precursors for carbon nanofibers. They can be fixed or even elongated during stabilization and subsequent carbonization to gain straight, mechanically robust carbon nanofibers. These processes necessitate additional equipment or are—if the nanofiber mats are just fixed at the edges—prone to resulti...