TY - JOUR AB - 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 core, again reducing stray fields. Here we theoretically investigate “Pac-Man” shaped iron nanostructures with varying aperture, i.e. structures ranging from a thin ring to a solid cylinder with a triangular cut. Our results show that in most cases, a vortex-like state without vortex core along the whole nanostructure occurs during magnetization reversal. Depending on the angle of the external magnetic field and the nanostructure thickness, different magnetization reversal processes have been found, including domain wall nucleation and propagation as well as small vortex states with cores. The occurrence of such special magnetic states can be attributed to the interaction of the shape anisotropy with the relatively high magneto-crystalline anisotropy of iron. Our simulations reveal the possibilities to use such structures for data storage applications as well as their importance in basic research, enabling formation of asymmetric magnetic structures beyond common onion and symmetric vortex states. AU - Bachar, Fatima-Zohra AU - Schröder, Christian AU - Ehrmann, Andrea ID - 1426 JF - Journal of Magnetism and Magnetic Materials KW - Magnetic nanostructures Micromagnetic simulation Magnetization reversal Iron Vortex state Domain walls Shape anisotropy SN - 03048853 TI - Magnetization reversal in Pac-Man shaped Fe nanostructures with varying aperture VL - 537 ER - TY - JOUR AB - 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 investigated in detail. It can be assumed that such beads will support domain wall formation due to a reduction of the relative impact of the shape anisotropy, in this way influencing magnetization reversal along the fiber. Here, we simulate magnetization reversal processes in iron, nickel, cobalt and magnetite fibers with a bead in the middle, produced in three typical dimensions gained by electrospinning. In most cases a vortex state occurs during magnetization reversal, independent from the material and the dimensions. For some angular orientations of the external magnetic field, double-vortex or meander states are visible, usually also followed by vortex states. These simulations underline the strong and highly reliable impact of beads along electrospun fibers, making these structures useful for data storage, transport and other applications. AU - Amini, Fedi AU - Blachowicz, Tomasz AU - Ehrmann, Andrea ID - 1616 JF - Journal of Magnetism and Magnetic Materials KW - Magnetic nanostructures Micromagnetic simulation Magnetization reversal Iron Nickel Cobalt Magnetite Vortex state Domain walls Shape anisotropy SN - 03048853 TI - Systematic study of magnetization reversal in beaded fibers from different magnetic materials VL - 529 ER - TY - JOUR AB - Magnetic vortices belong to the possibilities to store information in magnetic structures. Understanding their nucleation and propagation is also of interest in basic research. While vortices are usually examined in particles of homogeneous material, here we give an overview of the impact of borders between two materials, i.e. iron and permalloy, on magnetization reversal and vortex formation in double-wedges as well as adjacent rectangles of different thickness. While former investigations of pure iron nanoparticles of similar dimensions revealed different magnetization reversal magnetisms without vortex, with one or two vortices, the addition of a permalloy part stabilized the magnetization reversal so that in all situations under investigation, a single vortex was observed. Our simulations underline the technological importance of such double-material structures for the preparation of nanostructures for storage devices with reliable magnetization reversal processes, stable against erroneous modifications of nanoparticle dimensions and magnetic field orientations. AU - Sudsom, Devika AU - Blachowicz, Tomasz AU - Hahn, Lothar AU - Ehrmann, Andrea ID - 669 JF - Journal of Magnetism and Magnetic Materials KW - Magnetic nanostructures KW - Wedges KW - Micromagnetic simulation KW - Vortex KW - Magnetization reversal KW - Iron KW - Permalloy KW - Lithography SN - 0304-8853 TI - Vortex nucleation and propagation in magnetic double-wedges and semi-squares for reliable quaternary storage systems VL - 514 ER - TY - JOUR AB - Magnetic vortex structures are of high technological relevance due to their possible application in magnetic memory. Moreover, investigating magnetization reversal via vortex formation is an important topic in basic research. Typically, such vortices are only investigated in homogeneous magnetic materials of diverse shapes. Here, we report for the first time on micromagnetic simulation of vortex formation in magnetic bow-tie nanostructures, comprising alternating parts from iron and permalloy, investigated for two different thicknesses and under different angles of the external magnetic field. While no vortex was found in pure permalloy square, nanoparticles of the dimensions investigated in this study and in case of iron only a relatively thick sample allowed for vortex formation, different numbers of vortices and antivortices were found in the bow-tie structures prepared from both materials, depending on the angular field orientation and the sample thickness. By stabilizing more than one vortex in a confined nanostructure, it is possible to store more than one bit of information in it. Our micromagnetic simulations reveal that such bi-material structures are highly relevant not only for basic research, but also for data storage applications. AU - Sudsom, Devika AU - Juhász Junger, Irén AU - Döpke, Christoph AU - Blachowicz, Tomasz AU - Hahn, Lothar AU - Ehrmann, Andrea ID - 635 IS - 1 JF - Condensed Matter KW - magnetic nanostructures KW - micromagnetic simulation KW - bow-tie structure KW - vortex KW - magnetization reversal KW - iron KW - permalloy KW - lithography SN - 2410-3896 TI - Micromagnetic Simulation of Vortex Development in Magnetic Bi-Material Bow-Tie Structures VL - 5 ER - TY - JOUR AB - Magnetic nanostructures are investigated nowadays for diverse applications as well as in basic research. They often show unexpected magnetization reversal processes which are not only of high interest for understanding magnetization reversal processes on the nano-scale, but also due to their possible use in magneto-electronic devices, spintronics, neuromorphic computing and other areas. Square nano-frames prepared from iron, e.g., belong to the magnetic nano-particles exhibiting additional stable states at remanence which can be used for quaternary storage devices. The reason for this study is that nano-particles prepared from permalloy or nickel with their very low magneto-crystalline anisotropy do usually not show steps in the hysteresis loop and corresponding stable intermediate state, while the magneto-crystalline anisotropy of cobalt often dominates over the shape-anisotropy, resulting in a large number of steps which are not always stable. Here we report on experimental investigations by magneto-optic Kerr effect (MOKE) and micromagnetic simulations of square Co nano-frames, exhibiting steps along the slopes of the hysteresis loops. The positions and numbers of these steps varied during measurements without intentionally changing the experimental setup. Micromagnetic simulations were carried out to explain the experimental findings which could be attributed to different Co crystallite orientations, resulting in a modified magneto-crystalline anisotropy and thus different hysteresis loops for smallest variations of the laser beam position on the samples during MOKE measurements. AU - Blachowicz, Tomasz AU - Kosmalska, Dorota AU - Döpke, Christoph AU - Leiste, Harald AU - Hahn, Lothar AU - Ehrmann, Andrea ID - 582 JF - Journal of Magnetism and Magnetic Materials KW - Magnetic nanostructures Magneto-optical Kerr effect (MOKE) Micromagnetic simulation Magnetization reversal Cobalt Lithography TI - Varying steps in hysteresis loops of Co square nano-frames VL - 491 ER -