Nano Focus: Novel artificial spin structure produces rewriteable magnetic ice

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agnetic-storage devices, such as those used in computer hard disks, function on the binary principle—each of the two magnetic polarities represents 1 or 0. In order to increase storage capacity and functionalities, researchers have been studying artificial spin ices— structures wherein the constituents obey analogs of Pauling’s ice rule that dictates the positioning and ordering of protons in water ice. Artificial spin ices are magnetic systems with single-domain ferromagnetic nanostructures that have

team led by Yong-Lei Wang and Zhi-Li Xiao in the Materials Science Division at Argonne National Laboratory, proposed and validated a theoretical, artifi cial, magnetic charge ice structural design. The new structure suggests a different pattern of connections between magnetic charge pairs, leading to eight possible ordered states that could be controlled by external magnetic fields. These additional ordered states could provide a platform for designing future magneticstorage devices. “The novelty of this research is the new way of thinking: instead of focusing on spins, we tackled the associated magnetic charges that allow us to design and create artificial magnetic structures with more controllability,” says Wang, the Magnetic Field (mT) b corresponding author of this work. “This research not only introduces several new spin structures, but also provides a method for designing new artificial spin structures by decoupling spins and magnetic charges, which would greatly enrich the materials [selection] for [the] artificial spin ice community.” A magnetic force microscope (MFM) was demonstrated to manipulate the charge ordering. A two-dimensional solenoid magnet can apply inIllustration of rewriteable magnetic charge plane magnetic fields ice through charge configuration. (a) Experimental setup for global and local in any orientation for charge manipulation in a customized maglong-range tunability netic force microscopy. (b) Magnetization loop for write, erase, and read modes of of the entire magnetic a single magnetic spin. (c) Magnetic force spin ice sample. For microscope images of patterned magnetic charge ice at ground state, (d) fourfold delocal patterning of sevgenerate excited Type III state written at the eral magnetic charges, center, where (e) a smaller square was erased a magnetic tip of the back to ground state, and (f) a twofold degenerate excited Type II state was written MFM generates stray on the erased area. Credit: Yong-Lei Wang fields that interact with and Zhi-Li Xiao. individual magnetic charges. This provides

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potential applications in data storage, memory, and logic devices. Traditional artificial square spin ices have single-domain magnetic islands with only two ordered states, the magnetic moments either point inward or outward at the vertex of a square lattice. The large energy barrier required to rearrange the islands at room temperature limits the configuration of multiple ordered states for magnetic-storage applications. However, the assumption here is that connections between the pairs of

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