Abstract
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.
Highlights
Magnetic nanostructures can be produced with typical thicknesses of a few nanometers up to tens of nm and with lateral dimensions in the range of some 10 nm to several micrometers, applying lithographic techniques [1,2], pulsed electrodeposition [3] or self-assembly methods [4]
Magnetic nano-dots were especially investigated by diverse research groups, since they often enable the formation of a vortex which can be used for data storage [9,10]
Depending on the orientation with respect to the external magnetic field and on the sample thickness, in most cases two or four vortices were found, while the typical single-vortex state which is often visible in round or square nanodots of different materials and dimensions was fully suppressed by the bi-material structure
Summary
Magnetic nanostructures can be produced with typical thicknesses of a few nanometers up to tens of nm and with lateral dimensions in the range of some 10 nm to several micrometers, applying lithographic techniques [1,2], pulsed electrodeposition [3] or self-assembly methods [4] Such nanostructures are generally of high interest since the configurational anisotropy due to the shape of the nanoparticles can be in a similar order of magnitude as magneto-crystalline and magneto-elastic anisotropies, giving rise to new effects caused by the superposition of all these anisotropies [5,6,7,8]. Magnetic nano-dots were especially investigated by diverse research groups, since they often enable the formation of a vortex which can be used for data storage [9,10] One advantage of such vortex states is the reduction of stray fields and of interactions with neighboring nanoparticles [11,12], such interactions are not fully suppressed [13]. Flux-closed vortex states can be created in round, elliptical or square nano-rings without a core region, again reducing stray fields [14,15,16,17,18], while nano-dots of different shapes with a core region may enable formation of more magnetic states [19,20,21,22].
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