Magnetization reversal in bent nanofibers of different cross sections

Abstract

Artificial ferromagnetic nanofiber networks with new electronic, magnetic, mechanical and other physical properties can be prepared by electrospinning and may be regarded as the base of bio-inspired cognitive computing units. For this purpose, it is necessary to examine all relevant physical parameters of such nanofiber networks. Due to the more or less random arrangement of the nanofibers and the possibility of gaining bent nanofibers in this production process, elementary single nanofibers with varying bending radii, from straight fibers to those bent along half-circles, were investigated by micromagnetic simulations, using different angles with respect to the external magnetic field. As expected from the high aspect ratios and the resulting strong shape anisotropy, all magnetization reversal processes took place via domain wall processes. Changing the cross-section from circular to a circle-segment or a rectangle significantly altered the coercive fields and its dependence on the bending radius, especially for the magnetic field oriented perpendicular (90°) to the fiber axes. In all three cross-sections, an angle of 45° between the fiber orientation and the external magnetic field resulted in the smallest influence of the bending radius. The shapes of the longitudinal and transverse hysteresis curves showed strong differences, depending on cross-section, bending radius and orientation to the magnetic field, often depicting distinct transverse magnetization peaks perpendicular to the fibers for fibers which were not completely oriented parallel to the magnetic field. Varying these parameters thus provides a broad spectrum of magnetization reversal processes in magnetic nanofibers and correspondingly scenarios for a variety of fiberbased information processing.

Orientation of Electrospun Magnetic Nanofibers Near Conductive Areas

“…fine nanofibers [29][30][31]. Aligned electrospun magnetic nanofibers may also close the gap between fully determined nanofibers, as used in the racetrack memory [32], and arbitrarily oriented magnetic nanofibers [33], to enable stochastic behavior in biologically-inspired neuromorphic computing [34].…”

“…Especially for the case of magnetic nanofibers, a magnetic field-assisted electrospinning process was suggested to create oriented nanofibers [26][27][28]. A high alignment is of great interest for magnetic nanofibers to create a high magnetic anisotropy, based on the shape anisotropy of such fine nanofibers [29][30][31]. Aligned electrospun magnetic nanofibers may also close the gap between fully determined nanofibers, as used in the racetrack memory [32], and arbitrarily oriented magnetic nanofibers [33], to enable stochastic behavior in biologically-inspired neuromorphic computing [34].…”

Magnetic Properties of Electrospun Magnetic Nanofiber Mats after Stabilization and Carbonization

“…Notably, polyacrylonitrile (PAN) can be spun from the low-toxic solvent DMSO [3], making the whole process relatively easy to handle and avoiding unnecessary environmental pollution. In contrast to other methods of producing magnetic nanofibers, electrospinning usually creates nanofibers with different bending radii and forms a nanofiber mat without or with only low-fiber orientation [35][36][37], resulting in much more complicated magnetic anisotropies than straight, even nanofibers [38][39][40]. This makes electrospun nanofiber mats challenging for some applications, e.g., in racetrack memory, which usually consists of an array of parallel arranged magnetic nanowires and can theoretically store data series in some ten-to hundred-domain walls per nanowire [41].…”

Magnetic Nanofiber Mats for Data Storage and Transfer

“…The magnetization dynamics and quasistatic magnetic properties of such nanofibers were investigated theoretically and experimentally by different groups [20,21,22], indicating the large influence of the material, the fiber diameter and especially the orientation with respect to the external magnetic field on their magnetic properties [23,24]. It should be mentioned that opposite to common integrated circuits, hardware for neuromorphic computing needs a certain statistic approach, suggesting that randomly oriented nanofiber mats will show more interesting properties than perfectly aligned fibers with identical diameters and without bending radii.…”