Mixing a cocktail of topology and magnetism for future electronics
Joining topological insulators with magnetic materials for energy-
efficient electronics

Date:
August 5, 2021
Source:
ARC Centre of Excellence in Future Low-Energy Electronics
Technologies
Summary:
A new review throws the spotlight on heterostructures of topological
insulators and magnetic materials, where the interplay of magnetism
and topology can give rise to exotic quantum phenomena that are
promising building blocks for future low-power electronics. Provided
suitable candidate materials are found, a 'cocktail' of topological
physics and magnetism could produce these key states at room
temperature and without any magnetic field, making them a viable
ultra-low energy alternative to current, CMOS electronics.



FULL STORY ==========================================================================
A new Monash review throws the spotlight on recent research in
heterostructures of topological insulators and magnetic materials.


==========================================================================
In such heterostructures, the interesting interplay of magnetism and
topology can give rise to new phenomena such as quantum anomalous Hall insulators, axion insulators and skyrmions. All of these are promising
building blocks for future low-power electronics.

Provided suitable candidate materials are found, there is a possibility
to realise these exotic states at room temperature and without any
magnetic field, hence aiding FLEET's search for future low-energy,
beyond-CMOS electronics.

"Our aim was to investigate promising new methods of achieving the quantum
Hall effect," says the new study's lead author, Dr Semonti Bhattacharyya
at Monash University.

The quantum Hall effect (QHE) is a topological phenomenon that allows
high- speed electrons to flow at a material's edge, which is potentially
useful for future low- energy electronics and spintronics.

"However, a severe bottleneck for this technology being useful is the
fact that quantum Hall effect always requires high magnetic fields, which
are not possible without either high energy use or cryogenic cooling."
"There's no point in developing 'low energy' electronics that consume
more energy to make them work!" says Dr Bhattacharyya, who is a Research
Fellow at FLEET, seeking new generation of low-energy electronics.



========================================================================== However, a 'cocktail' of topological physics and magnetism can make it
possible to achieve a similar effect, the quantum anomalous Hall effect,
where similar edge states appear without applying external magnetic field.

Several strategies have been followed to induce magnetism in topological insulators:
1. by incorporating magnetic impurity, 2. by using intrinsically
magnetic topological insulators 3. by inducing magnetism through a
proximity effect in topological
insulator-magnetic insulator heterostructures.

"In our review, we focussed on the recent scientific research into heterostructures on the third approach," says co-author Dr Golrokh Akhgar (FLEET/Monash). Ie, a single structure incorporating thin-film layers of topological insulators and magnetic materials adjacent to each other,
allowing the topological insulator to borrow magnetic properties from
its neighbour.

This approach allows researchers to tune each type of material, for
example increasing the critical temperature for the magnetic material,
and increasing the band gap, and decreasing the defect states, in
topological materials.

"We think this approach for inducing magnetism in topological insulators
is the most promising for future breakthroughs, because the magnetism
and topology can be individually tuned in two different materials,
thereby optimizing both to our advantage," says co-author Matt Gebert (FLEET/Monash).



========================================================================== Another important feature of this heterostructure is that the induced
magnetism only depends on the magnetic moments of the nearest plane
inside the magnetic material, hence the magnetic materials do not have
to be ferromagnets - - ferrimagnets, or antiferromagnets can also
be used. This increases the number of candidate magnetic materials,
allowing choice of materials with magnetism at higher temperatures,
for operation closer to room temperature.

"This is an exciting new field of research," says corresponding author
Prof Michael Fuhrer, also at Monash University.

"Progress is happening extremely rapidly, and we felt it was time for a
review article summarizing the recent accomplishments, and outlining a
future roadmap of this field," says Prof Fuhrer, who is director of FLEET.

This review provides all the information necessary to introduce new
researchers to the field. It explains the conceptual ideas behind
the mechanisms of magnetic proximity effect in topological insulators, introduces the materials systems that have been explored and the various emergent phenomenon that have been detected, and outlines a future
roadmap towards increasing the temperature and innovative applications.

"We hope others will find it a timely review clarifying the important
concepts of the field and recent publications," says Semonti.

========================================================================== Story Source: Materials provided by ARC_Centre_of_Excellence_in_Future_Low-Energy_Electronics
Technologies. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Semonti Bhattacharyya, Golrokh Akhgar, Matthew Gebert, Julie
Karel, Mark
T. Edmonds, Michael S. Fuhrer. Recent Progress in Proximity Coupling
of Magnetism to Topological Insulators. Advanced Materials, 2021;
2007795 DOI: 10.1002/adma.202007795 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210805115442.htm

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