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 - Asymmetric magnetic hysteresis loops are usually found in exchange bias (EB) systems, typically after field cooling a system below the Néel temperature of an antiferromagnet exchange coupled to a ferromagnet. Alternatively, asymmetric hysteresis loops may occur due to undetected minor loops or in systems with a rotational anisotropy. Here, we report on an exchange bias thin film system MgO(100)/Co/CoO, examined at room temperature, which is far above the blocking temperature, by the magneto-optical Kerr effect (MOKE). While the longitudinal hysteresis loops partly show steps which are well-known from diverse purely ferromagnetic systems, the transverse hysteresis loops exhibit clear asymmetries, similar to exchange biased systems at low temperatures, and unusual transverse magnetization values at saturation. Since minor loops and a rotational anisotropy can be excluded in this case, this asymmetry can possibly be a residue of the exchange bias coupling at lower temperatures. AU - Ehrmann, Andrea AU - Blachowicz, Tomasz ID - 678 IS - 4 JF - Condensed Matter KW - exchange bias KW - rotatable anisotropy KW - blocking temperature KW - minor loops KW - Co/CoO SN - 2410-3896 TI - Asymmetric Hysteresis Loops in Co Thin Films VL - 5 ER -