Andreas Schmid (left) and Gong Chen (right) with the SPLEEM instrument at Berkeley Lab. Photo: Roy Kaltschmidt/Berkeley Lab.
Andreas Schmid (left) and Gong Chen (right) with the SPLEEM instrument at Berkeley Lab. Photo: Roy Kaltschmidt/Berkeley Lab.

Researchers working at the US Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) have coupled graphene, a monolayer form of carbon, with thin layers of magnetic materials like cobalt and nickel to produce exotic behavior in electrons that could be useful for next-generation computing.

The work was performed in collaboration with French scientists, including Nobel Laureate Albert Fert, an emeritus professor at Paris-Sud University and scientific director of a research laboratory in France. The team performed key measurements at Berkeley Lab's Molecular Foundry, a DOE Office of Science User Facility focused on nanoscience research.

Fert shared the Nobel Prize in Physics in 2007 for his work in understanding a magnetic effect in multilayer materials that led to applications such as new technology for reading data in hard drives. The work also gave rise to a new field studying how to exploit and control a fundamental property in electrons known as ‘spin’ to drive a new type of low-energy, high-speed computer memory and logic technology known as spintronics.

In this latest work, reported in a paper in Nature Materials, the research team showed how spin property – analogous to a compass needle that can be tuned to face either north or south – can be affected by the interaction between the graphene and magnetic layers in a material.

The researchers found that the material's electronic and magnetic properties create tiny swirling patterns where the layers meet, which gives hope for controlling the direction of these swirls and tapping this effect for a form of spintronics applications known as ‘spin-orbitronics’ in ultrathin materials. The ultimate goal is to store and manipulate data quickly and efficiently at very small scales, and without the heat build-up that is a common hiccup for miniaturizing computing devices.

Typically, researchers working to harness this effect have coupled heavy and expensive metals like platinum and tantalum with magnetic materials. But graphene offers a potentially revolutionary alternative since it is ultrathin, lightweight, has very high electrical conductivity and can also serve as a protective layer for corrosion-prone magnetic materials.

"You could think about replacing computer hard disks with all solid state devices – no moving parts – using electrical signals alone," said Andreas Schmid, a staff scientist at the Molecular Foundry who participated in the research. "Part of the goal is to get lower power-consumption and non-volatile data storage."

The latest research represents an early step toward this goal, Schmid noted, and a next step is to control nanoscale magnetic features called skyrmions, which can exhibit a property known as chirality that makes them swirl in either a clockwise or counter-clockwise direction.

In more conventional layered materials, electrons traveling through the materials can act like an ‘electron wind’ that changes magnetic structures like a pile of leaves blown by a strong wind, Schmid said. In contrast, the strong electron spin effects in the new graphene-layered material can drive magnetic textures of opposite chirality in different directions as a result of the ‘spin Hall effect’, which explains how electrical currents can affect spin and vice versa. If that chirality can be universally aligned across a material and flipped in a controlled way, researchers could use it to process data.

"Calculations by other team members show that if you take different magnetic materials and graphene and build a multilayer stack of many repeating structures, then this phenomenon and effect could possibly be very powerfully amplified," Schmid said.

To measure the layered material, scientists applied spin-polarized low-energy electron microscopy (SPLEEM) using an instrument at the Molecular Foundry's National Center for Electron Microscopy. This is one of just a handful of specialized devices around the world that allow scientists to combine different images to essentially map the orientations of a sample's three-dimensional magnetization profile (or vector), revealing its ‘spin textures’.

The research team also created the samples using the same SPLEEM instrument through a precise process known as molecular beam epitaxy, and separately studied the samples using other forms of electron-beam probing techniques.

Gong Chen, a co-lead author who participated in the study as a postdoctoral researcher at the Molecular Foundry but is now an assistant project scientist in the University of California, Davis Physics Department, said the collaboration sprang out of a discussion with French scientists at a conference in 2016. Both groups had independently been working on similar research and realized the synergy of working together.

While the effects the researchers have observed in these latest experiments had been discussed decades ago in previous journal articles, Chen noted that the concept of using an atomically thin material like graphene in place of heavy elements to generate those effects was a new concept.

"It has only recently become a hot topic," Chen said. "This effect in thin films had been ignored for a long time. This type of multilayer stacking is really stable and robust."

Using skyrmions could be revolutionary for data processing, he said, because information can potentially be stored at much higher densities than is possible with conventional technologies, and with much lower power usage. Molecular Foundry researchers are now working to form the graphene-magnetic multilayer material on an insulator or semiconductor to bring it closer to potential applications, Schmid said.

This story is adapted from material from Lawrence Berkeley National Laboratory, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.