A Twist in Electronics

A Twist in Electronics
Figure. Left, device layout with a superimposed Magneto-optical Kerr effect (MOKE) image of magnetic domains in Tm3Fe5O12 (TmIG). Right, MOKE images showing the displacement of skyrmions driven by current pulses. The topological charge of the skyrmions, which can be controlled by the polarity of the skyrmion core (bright/dark contrast), results in a transverse deflection of the skyrmions.

Magnetic skyrmions are topological spin textures that hold potential for the development of ultra-dense nonvolatile memories and post-von Neumann computing schemes. IFIMAC Junior Group Leader Saül Vélez together with colleagues at ETH Zurich demonstrate that magnetic skyrmions can be stabilized and manipulated by proximity electric currents in magnetic insulators.

The ability of the electron spins to manipulate the magnetization of small magnetic elements is a fundamental principle of modern electronics. Tell-tale examples are found in the electric switching of magnetic tunnel junctions, which is key in the magnetic random-access memory technology, as well as in the controlled displacement of magnetic textures that can be used as information bits in nanowires. In particular, skyrmions –which are continuous swirls of the magnetization– are ideal candidates for device applications due to their enhanced stability compared to ordinary magnetic textures, high-density storage capabilities, and the possibility to enable novel logic and computation schemes. Most studies in this area, however, have been performed on metallic ferromagnets, which suffer from resistive losses and are limited in frequency. Insulating ferrimagnets such as garnet materials are ideal candidates to surpass these limitations, but realizing electronic devices based on insulating magnetic media is a challenge.

In a recent work published in Nature Nanotechnology, Saül Vélez and co-workers demonstrate that skyrmions can be stabilized in ferrimagnetic insulators and manipulated by electric currents in thin-film metal-insulator heterostructures. Moreover, they show that intentional distortions of the magnetic texture induced by coupling the structure to a second magnetic layer can lead to a ratchet-like current-driven motion of chiral domain walls and skyrmions. “This new effect can be exploited to control the flow of information in devices or for extracting a net motion of the magnetic textures from electric pulses of alternating polarity” says Prof. Pietro Gambardella, leader of the Intermag group at ETH Zürich and co-supervisor of the project.

“Our next goal is to exploit the unique properties of these materials to reduce the skyrmion size to sub-20 nm in diameter and to increase the skyrmion mobility to relativistic solitonic velocities”, adds Saül Vélez. The progress in the development of skyrmion devices has been limited because of the lack of appropriate materials and device structures. The use of ferrimagnetic insulators as active media is a twist to conventional electronic device approaches and shows prospects for the development of novel skyrmion memory and logic technologies. [Full article]

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