Unlocking magnetic properties for future faster, low-energy spintronics

A theoretical-experimental collaboration across two FLEET nodes has discovered new magnetic properties within 2D structures, with exciting potential for researchers in the emerging field of ‘spintronics’.

Spintronic devices use a quantum property known as ‘spin’, in addition to the electronic charge of conventional electronics.

Spintronics thus promise ultra-high speed low-energy electronic devices with significantly enhanced functionality.

The RMIT-UNSW study discovered never-before-seen magnetic properties in devices known as vdW hetero-structures comprising several layers of novel, 2D materials.

The latest results show that vdW spintronics could provide devices with more functionality, comparing with the traditional spintronic approaches. Further research could generate devices with significant industrial applications.

BACKGROUND

Two-dimensional (2D) ferromagnetic van-der-Waals (vdW) materials have recently emerged as effective building blocks for a new generation of ‘spintronic’ devices.

When layered with non-magnetic vdW materials, such as graphene and/or topological insulators, vdW hetero-structures can be assembled to provide otherwise unattainable device structures and functionalities.

The material studied was 2D Fe₃GeTe₂ (FGT), a metal found to display promising ferromagnetic properties for spintronic devices in a previous FLEET study.

SURPRISING DISCOVERIES

“We discovered a previously unseen mode of giant magneto-resistance (GMR) in the material, says FLEET PhD and study co-author Sultan Albarakati.

Unlike the conventional, previously-known two GMR states (ie, high resistance and low resistance) that occur in thin-film hetero-structures, the researchers also measured antisymmetric GMR with an additional, distinct intermediate resistance state.

“This reveals that vdW ferromagnetic hetero-structures exhibit substantially different properties from similar structures,” says Sultan.

This surprising result is contrary to previously held beliefs regarding GMR. It is suggestive of different underlying physical mechanisms in vdW hetero-structures, with potential for improved magnetic information storage.

Theoretical calculations indicate that the three levels of resistance are the result of spin-momentum-locking induced spin-polarised current at the graphite/FGT interface.

“This work has significant interest for researchers in 2D materials, spintronics, and magnetism,” says co-author FLEET PhD Cheng Tan. “It means that ‘traditional’ tunnelling magnetoresistance devices, spin-orbit torque devices and spin transistors may reward re-investigated using similar vdW hetero-structures to reveal similarly surprising characteristics.”

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THE STUDY

The study ‘Antisymmetric giant magnetoresistance in van der Waals Fe₃GeTe₂/graphite/Fe₃GeTe₂ tri-layer heterostructures’ was published in Science Advances today (July 2019). (arXiv)

As well as support by the Australian Research Council, the authors acknowledge the support of the National Key Research and Development Program (China) and the Institute for Information & Communications Technology Promotion (South Korea).

COLLABORATION

The experiment’s detailed electron transport measurements were performed by a collaboration of researchers led by FLEET CI Prof Lan Wang (RMIT) and FLEET Deputy Director Prof Alex Hamilton (UNSW), using hetero-structures and devices fabricated by Prof Wang’s team at RMIT.

Theoretical studies were led by FLEET CI Dr Dimi Culcer (UNSW), while data analysis was undertaken by teams comprising both RMIT and UNSW researchers.

Electronic band structure calculations were led by Yunjun Zhao at the South China University of Technology (China).

The source study material was synthesised by a team of researchers from the Center for Quantum Materials and Superconductivity (CQMS) and the Chinese Academy of Sciences.

The research was initially conceived and designed by Lan Wang at RMIT.

NANO-FABRICATION AT FLEET

VdW hetero-structures are used to study the properties of novel materials at FLEET, an Australian Research Council Centre of Excellence.

The Centre for Future Low-Energy Electronics Technologies (FLEET) is a collaboration of over a hundred researchers, seeking to develop ultra-low energy electronics to face the challenge of energy use in computation, which already consumes 8% of global electricity, and is doubling each decade.

FLEET’s research sits at the very boundary of what is possible in condensed-matter physics. At the nano scale, nanofabrication of functioning devices will be key to the Centre’s success.

Specialised techniques needed to integrate novel atomically-thin, two-dimensional (2D) materials into high-quality, high-performance nano-devices are coordinated within the Centre’s Enabling technology B, led by RMIT’s Lan Wang.

This collaboration between FLEET’s UNSW and RMIT teams is typical of the Centre’s nano-device research, which links many of FLEET’s groups and nodes. Some groups bring expertise in device fabrication, while other groups are strong in device characterisation. Such teamwork, fundamental to modern science, is expedited by the Australian Research Council Centre of Excellence system.