Thinning down for enhanced magnetic properties

The unusual electronic and magnetic properties of van der Waals (vdW) materials, made up of many ‘stacked’ two-dimensional (2D) layers, offer potential for future electronics, including spintronics. Researchers with the Australian Research Council’s Centre of Excellence in Future Low-Energy Electronics Technologies (FLEET), based at RMIT University in Australia, have now found one particularly promising candidate material, Fe₃GeTe₂ (FGT) – provided it’s created in layers only 200 millionths of a millimeter in thickness.

This pioneering work, which is reported in a paper in Nature Communications, paves the way for a new research field: vdW heterostructure based spintronics.

Two-dimensional vdW materials are potential building blocks for new, high-performance electronic, electro-optic and photonic devices. But their application in spintronics has been limited because so few materials display the required magnetic properties.

For serious consideration in spintronics, a vdW ferromagnetic metal with hard magnetic properties and a near square-shaped hysteresis loop is indispensable. Perpendicular magnetic anisotropy is also favorable.

“It is exciting, pioneering work. And it paves the way for a new research field: vdW heterostructures-based spintronics.”Lan Wang, FLEET

FLEET’s RMIT researchers performed anomalous Hall effect measurements on single-crystal Fe₃GeTe₂ (FGT) nanoflakes, resolving the desired magnetic properties when the thickness of the sample was reduced to less than 200nm. This motivated the researchers to investigate FGT’s improved properties at atomic-scale thicknesses.

“FGT has long been considered a promising vdW ferromagnetic metal,” explains lead author Cheng Tan. “But its ferromagnetic properties suggested limited potential as a building block for vdW magnetic heterostructures.”

Those properties strongly depend on thickness-dependent domain structure, and molecular beam epitaxy (MBE)-grown, wafer-scale FGT thin films are known to have improved magnetic properties. “So we reduced thickness and kept measuring,” explains Tan.

Hall effect measurements on single-crystal FGT nanoflakes confirmed that the magnetic properties are highly dependent on thickness. By reducing the thickness to less than 200nm, the required characteristics could be achieved, making vdW FGT a ferromagnetic metal suitable for vdW heterostructure-based spintronics. Other researchers will now build on these results.

To better identify other candidate materials, the researchers also developed a model that can be generalized for vdW ferromagnetic thin films or nanoflakes. This model will open new research paths for those studying the possible existence of magnetic coupling between vdW atomic layers.

“It is exciting, pioneering work,” says research theme leader Lan Wang. “And it paves the way for a new research field: vdW heterostructures-based spintronics.”

Stacked with other vdW nanoflakes, Fe₃GeTe₂ nanoflakes could be used in a variety of devices exhibiting giant magnetoresistance and tunneling magnetoresistance. Spin orbit torque and spin field effect transistor devices are further possibilities.

The opportunity exists to design and fabricate many devices based on vdW magnets, such as magnetizing 2D topological insulators or stacking vdW ferromagnetic metals for spin–orbit torque devices.

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