In computers, information is transmitted through semiconductors by the movement of electrons and is stored in the direction of electron spin in magnetic materials. To shrink devices while improving their performance – a goal of an emerging field called spintronics (“spintronics”) – researchers are looking for unique materials that combine quantum properties. In the journal Nature Materials, a team of chemists and physicists in Colombia found a strong link between electron transfer and magnetism in a material called chromium sulfide bromide (CrSBr).
Created in the lab of chemist Xavier Roy, CrSBr is a so-called van der Waals crystal that can be peeled back into stackable 2D layers that are just a few atoms thin. In contrast to related materials that are rapidly destroyed by oxygen and water, CrSBr crystals are stable at ambient conditions. These crystals also maintain their magnetic properties at a relatively high temperature of -280 degrees Fahrenheit, obviating the need to cool expensive liquid helium to -450 degrees Fahrenheit.
Colleagues Nathan Wilson and Xiaodong Xu of the University of Washington and Xiaoyang Zhou in Columbia have found a link between magnetism and how CrSBr responds to light, said Evan Telford, a postdoctoral researcher in Roy’s lab who received a Ph.D. in physics from Columbia in 2020. In the present work, Telford has led efforts to explore its electronic properties.
The team used an electric field to study the CrSBr layers across different electron densities, magnetic fields and temperatures — different parameters that can be tweaked to produce different effects in a material. As the electronic properties of CrSBr changed, so did its magnetism.
“Semiconductors have tunable electronic properties. Magnets have tunable spin configurations. In CrSBr, these two handles are combined,” Roy said. “This makes CrSBr attractive both for basic research and for potential dental electronics applications.”
Telford explained that magnetism is a property that is difficult to measure directly, especially as the size of a material shrinks, but it is easy to measure how electrons move with a parameter called resistance. In CrSBr, the resistance can act as a proxy for unobservable magnetic states. “This is very powerful,” Roy said, especially as researchers are looking to one day build chips out of two-dimensional magnets, which can be used for quantum computing and for storing huge amounts of data in a small space.
Telford said the link between the material’s electronic and magnetic properties was due to imperfections in the layers — for the team, he was lucky. “People usually want the cleanest material possible,” he said. “Our crystals have flaws, but without them, we wouldn’t have noticed this pairing.”
From here, Roy’s lab is testing ways to grow peelable van der Waals crystals with intentional defects, to improve the ability to fine-tune the material’s properties. They are also exploring whether different combinations of elements can function at higher temperatures while retaining these valuable aggregate properties.
Visualize the atomic and magnetic structure of two-dimensional magnetic insulators
Evan J. Telford et al, Coupling between magnetic ordering and charge transfer in a two-dimensional magnetic semiconductor, nature materials (2022). DOI: 10.1038 / s41563-022-01245-x
Submitted by Columbia University Quantum Initiative
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