Rotating ultra-small magnetic vortices were detected in iron-containing materials

April 02, 2023

(Nanowerk News) Microelectronics form the basis of much of today’s modern technology, including smartphones, laptops, and even supercomputers. It is based on the ability to allow and stop the flow of electrons through a material. Electronic spin, or spintronics, are spin-offs. It is based on the spin of electrons, and the fact that spin of electrons together with electric charges creates a magnetic field.

“This property could be exploited for building blocks in the memory storage of future computers, such as brains and other new computing systems, and high-efficiency microelectronics,” said Charudatta Phatak, group leader in the Materials Science division at the US Department of Energy’s (DOE) Argonne National Laboratory.

A team including researchers at Argonne and the National High Magnetic Field Laboratory (MagLab) discovered surprising properties in the magnetic materials iron, germanium, and tellurium. This material is in the form of thin sheets that are only a few to 10 atoms thick. These are called 2D ferromagnets.

The team found that two types of magnetic fields can coexist in this ultrathin material. Scientists call them Meron and Skyrmion. They are like swirling mini-storm systems dotting the flat ferromagnetic landscape. But they differ in size and circling behavior. The simulation captures the distinct eddy texture of skyrmions and merons observed in ferromagnet thin films. (Image by University of Edinburgh/based on microscopy images collected by Argonne on samples prepared at MagLab)

Known and studied for about 15 years, skyrmions are about 100 nanometers – roughly the size of a single virus molecule – and their magnetic fields flow in intricate patterns, resembling a knot in a string. Recently discovered, merons are roughly the same size and have a magnetic field that swirls around like a whirlpool.

“Both the skyrmion and meron are very stable because like a tightly tied knot, they are difficult to untangle,” said Luis Balicas, who held the joint meeting at MagLab and Florida State University. “This stability together with their magnetic properties make them attractive as carriers of information.”

The team is the first to observe both of these magnetic textures on a thin film at the same time at low temperatures, from minus 280 to minus 155 degrees Fahrenheit. Also, meron persists down to room temperature, an important consideration for exploiting it in practical devices. In the past, they were only observed at much lower temperatures in different materials.

The team also showed that skyrmions and merons can be detected by their effect on a given current, by measuring the voltage. This feature means they can adapt to the binary code used in all digital computers. This code consists of a combination of 1 and 0. In a spintronic device, a 1 will be indicated by an electrical signal that detects a skyrmion or meron. The absence of an electrical signal will then convey 0.

Detecting and characterizing different magnetic textures in films less than ten atoms thick requires specialized scientific tools. Argonne physicist Yue Li led the challenging task using an instrument called a Lorentz transmission electron microscope (TEM). This microscope has aberration correction technology to increase its resolution. This TEM can visualize the magnetization of materials at the nanoscale under different magnetic fields over a wide temperature range, a unique capability available in Argonne. The range ranges from minus 280 Fahrenheit to room temperature.

The team performed additional magnetic imaging and more at Argonne’s Center for Nanoscale Materials, a DOE Office of Science user facility.

“More basic research is needed to fully understand the behavior of skyrmions and merons under different conditions, and how to use them in information coding,” said Balicas. “There seems to be a lot of sci-fi schemes out there. We can’t predict the future, but it looks like one or more will come to fruition.”

The research has been published in Advanced Materials (“Coexistence of Merons with Skyrmions in Centrosymmetric Van Der Waals Ferromagnet Fe5–xGeTe2).

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