Research Article Influence of the Distance between Nanoparticles in Clusters on the Magnetization Reversal Process Andrea Ehrmann 1 and Tomasz Blachowicz 2 1 Faculty of Engineering and Mathematics, Bielefeld University of Applied Sciences, Interaktion 1, 33619 Bielefeld, Germany 2 Institute of Physics-Center for Science and Education, Silesian University of Technology, Ul. Konarskiego 22B, 44-100 Gliwice, Poland Correspondence should be addressed to Andrea Ehrmann; andrea.ehrmann@f-bielefeld.de Received 27 March 2017; Accepted 12 July 2017; Published 20 August 2017 Academic Editor: Anil Annadi Copyright © 2017 Andrea Ehrmann and Tomasz Blachowicz. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Fourfold magnetic nanoparticles, created from nanowires or in the form of an open square, ofer the possibility of creating quaternary memory devices with four unambiguously distinguishable stable states at remanence. Tis feature, however, has been simulated for single magnetic nanoparticles or clusters with interparticle distances similar to the nanoparticle dimensions. For the possible use in bit-patterned media, it is important to understand the scaling behavior of the stability of the additional intermediate states with the interparticle distance. Te paper investigates exemplarily nanoparticles of two shapes which were found to be optimum to gain four states at remanence. For clusters of these particles, the probability of reaching the additional intermediate states in all particles in the same feld region is strongly reduced with decreased interparticle distance. Te diferences between both shapes indicate possible solutions for this problem in the form of new nanoparticle shapes. 1. Introduction Magnetic nanoparticles are of technological interest, for example, for magnetic storage media, magnetic sensors, and MRAMs [1–3]. Since their overall anisotropy is governed by the shape anisotropy [4], tailoring a nanoparticle’s form allows for adjusting its magnetic properties. Tis is important for the possible use of nanoparticles in bit-patterned media or other applications in which defned anisotropies are necessary. One possible shape consists of a fourfold ring with diferent shape modifcations, leading to two additional magnetic states at remanence which could be used to create quaternary memory systems [5]. In this way, data storage density could be increased by increasing the number of bits per particle instead of increasing the particle density. Tis approach has also been followed by other groups, resulting in three, four, or up to eight magnetization states in diverse nanostructures [6–10]. Problematic in all these magnetic systems, however, is the interaction between neighboring nanostructures, ofen strongly modifying the single nanoparticle’s magnetic prop- erties. For multilayer systems, for example, distances of 30 nm were found to be sufcient to approximate independent mag- netic behavior of the layers [11]. In an array of nanotubes with distances of 30 nm or 60 nm, however, even the larger dis- tance showed a signifcant infuence of the cluster structure on magnetization reversal, especially by nearly completely annihilating a step in the hysteresis loop which occurred for single nanotubes of identical geometry [12]. Since such a step is also necessary for reaching stable intermediate states at remanence, this fnding indicates possible problems with downscaling the fourfold ring structure under investigation here. For a large cluster of nanodots, the geometric shape in which the lowest stray felds and thus the smallest infuences between nanoparticles can be expected, nearly random mag- netization orientations were found lately [13]. Nevertheless, for the systems under investigation here, it was found in an another project that nanoparticles with diameters of 120 nm and identical interparticle distances did nearly not change their coercive felds and retained a collective intermediate onion state which is necessary for the creation of quaternary memory devices [14]. Due to the necessity to further minimize such nanoparticle clusters, it is, however, necessary to investigate the infuence of further Hindawi Journal of Nanomaterials Volume 2017, Article ID 5046076, 6 pages https://doi.org/10.1155/2017/5046076