Reviewing multiferroics for future, low-energy data storage

Date:
October 22, 2020
Source:
ARC Centre of Excellence in Future Low-Energy Electronics
Technologies
Summary:
Big data and exponential demands for computations are driving an
unsustainable rise in global ICT energy use. A new study reviews
the use of the 'multiferroic' material bismuth-ferrite, which
allows for low- energy switching in data storage devices and could
be applied in a future generation of ultra-low-energy electronics.



FULL STORY ==========================================================================
A new UNSW study comprehensively reviews the magnetic structure of the multiferroic material bismuth ferrite (BiFeO3 -- BFO).


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The review advances FLEET's search for low-energy electronics, bringing together current knowledge on the magnetic order in BFO films, and
giving researchers a solid platform to further develop this material in low-energy magnetoelectric memories.

BFO is unique in that it displays both magnetic and electronic ordering
(ie, is 'multiferroic') at room temperature, allowing for low-energy
switching in data storage devices.

MULTIFERROICS: COMBINED MAGNETIC AND ELECTRONIC ORDERING FOR LOW-ENERGY
DATA STORAGE Multiferroics are materials that have more than one 'order parameter'.

For example, a magnetic material displays magnetic order: you can imagine
that the material is made up of lots of neatly arranged (ordered),
tiny magnets.



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BFO cycloid diagram Spin (magnetic order) in the multi-ferroic
material bismuth-ferrite 'cycles' through the crystal, offering
potential application in emerging electronics fields such as magnonics
Some materials display electronic order -- a property referred to as ferroelectricity -- which can be considered the electrical equivalent
of magnetism.

In a ferroelectric material, some atoms are positively charged, others
are negatively charged, and the way these atoms are arranged in the
material gives a specific order to the charge in the material.

In nature, a small fraction of known materials possess both magnetic
and ferroelectric order (as is the case for BFO) and are thus referred
to as multiferroic materials.



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The coupling between magnetic and ferroelectric order in a multiferroic material unlocks interesting physics and opens the way for applications
such as energy-efficient electronics, for example in non-volatile
memory devices.

Studies at FLEET focus on the potential use of such materials as a
switching mechanism.

Ferroelectric materials can be considered the electrical equivalent of a permanent magnet, possessing a spontaneous polarisation. This polarisation
is switchable by an electric field.

The storage of data on traditional hard disks relies on switching
each bit's magnetic state: from zero, to one, to zero. But it takes a relatively large amount of energy to generate the magnetic field required
to accomplish this.

In a 'multiferroic memory,' the coupling between the magnetic and
ferroelectric order could allow 'flipping' of the state of a bit by
electric field, rather than a magnetic field.

Electric fields are a lot less energetically costly to generate than
magnetic fields, so multiferroic memory would be a significant win for ultra-low-energy electronics, a key aim in FLEET.

BFO: A UNIQUE MULTIFERROIC MATERIAL Bismuth ferrite (BFO) is unique
among multiferroics: its magnetic and ferroelectric persist up to room temperature. Most multiferroics only exhibit both order parameters
at far below room temperature, making them impractical for low-energy electronics.

(There's no point in designing low-energy electronics if it costs you
more energy to cool the system than you save in operation.) THE STUDY Co-author Dr Dan Sando preparing materials for study at UNSW The new UNSW
study reviews the magnetic structure of bismuth ferrite; in particular,
when it is grown as a thin single crystal layer on a substrate.

The paper examines BFO's complicated magnetic order, and the many
different experimental tools used to probe and help understand it.

Multiferroics is a challenging topic. For example, for researchers trying
to enter the field, it's very difficult to get a full picture on the
magnetism of BFO from any one reference.

"So, we decided to write it," says Dr Daniel Sando. "We were in the
perfect position to do so, as we had all the information in our heads,
Stuart wrote a literature review chapter, and we had the combined
necessary physics background to explain the important concepts in a tutorial-style manner." The result is a comprehensive, complete, and
detailed review article that will attract significant attention from researchers and will serve as a useful reference for many.

Co-lead author Dr Stuart Burns explains what new researchers to the field
of multiferroics will gain from the article: "We structured the review as
a build-your-own-experiment starter pack: readers will be taken through
the chronology of BFO, a selection of techniques to utilize (alongside
the advantages and pitfalls of each) and various interesting ways to
modify the physics at play. With these pieces in place, experimentalists
will know what to expect, and can focus on engineering new low-energy
devices and memory architectures." The other lead author, Oliver Paull,
says "We hope that other researchers in our field will use this work
to train their students, learn the nuances of the material, and have a
one-stop reference article which contains all pertinent references --
the latter in itself an extremely valuable contribution." Prof Nagy
Valanoor added "The most fulfilling aspect of this paper was its style
as a textbook chapter. We left no stone unturned!" The discussion paper includes incorporation of BFO into functional devices that use the cross coupling between ferroelectricity and magnetism, and very new fields such
as antiferromagnetic spintronics, where the quantum mechanical property
of the spin of the electron can be used to process information.


========================================================================== 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. Stuart R. Burns, Oliver Paull, Jean Juraszek, Valanoor Nagarajan,
Daniel
Sando. The Experimentalist's Guide to the Cycloid, or Noncollinear
Antiferromagnetism in Epitaxial BiFeO 3. Advanced Materials, 2020;
2003711 DOI: 10.1002/adma.202003711 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201022112622.htm

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