Magnonics (the study of excitations in a magnetic material) may well replace electronics as the basis of modern computing. This would drastically increase energy efficiency and provide devices that can be miniaturized beyond the limit of current technology. However, the control of magnetic textures in nano-sized magnets is not straightforward to achieve. A team of researchers in Brazil and Chile have found a novel and elegant way to create stable magnetic configurations that had previously not been possible.
The direction of magnetization within a ferromagnetic material may take on many exotic configurations. For example, a vortex forms when the magnetization spirals inward towards a single point. Such magnetic textures appear in domain walls and as ground-state configurations in some sub-micron-sized magnetic elements.
An antivortex is formed when the magnetization spirals outwards from a single point and has an opposite winding number to a vortex. The ability to manipulate magnetization vortex–antivortex pairs opens up a number of potential applications in computing and data storage. However, while stable vortices have been observed in various systems, a stable antivortex had proved difficult to obtain. Now, Smiljan Vojkovic and colleagues at Pontificia Universidad Católica de Chile, Universidad de Chile in Chile, and Instituto Federal de Educação, Ciência e Tecnologia Baiano and Universidade Federal de Viçosa in Brazil have cracked it by incorporating curvature into their nanomagnets.
The twist with donuts
Inducing a strong curvature in a magnetic material breaks the inversion symmetry, giving rise to a twist in the magnetization, with the direction of the twist depending on whether the curve is positive like a sphere or negative like a hyperboloid. The research team designed and modelled a nanomagnet in the shape of a hollow doughnut-shape, or torus, which has negative curvature on the internal border and positive on the external border. They exposed this to an external magnetizing field in the plane of the torus and monitored the remnant magnetization left behind after this field was removed. Indeed, at each of these borders a stable vortex or antivortex was formed according to the direction of the curvature.
The next challenge for the researchers is to manipulate these vortex–antivortex pairs. If it is possible to transfer the pair to a straight wire without damage, magnetization-based logic operations may become possible. “Race-track” memory devices could be designed around these magnetic configurations, which would allow data storage density to exceed the fundamental limit of current devices. Furthermore, the use of an oscillating external field would lend these structures to the design of nanoscale antennas.
More details can be found in the original article in the Journal of Applied Physics.
