Australian experts are looking at new materials that could guide the future of low-energy data storage.

Big data and exponential demands for computations are driving an unsustainable rise in global ICT energy use.

A new UNSW 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.

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.

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.

New studies at the ARC Centre of Excellence in Future Low-Energy Electronics Technologies (FLEET) focus on the potential use of such materials as a switching mechanism.

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.

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.

For researchers trying to enter the field, it is 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.

“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,” says co-lead author Dr Stuart Burns

“With these pieces in place, experimentalists will know what to expect, and can focus on engineering new low-energy devices and memory architectures.”

More information is available in The Experimentalist’s Guide to the Cycloid, or Noncollinear Antiferromagnetism in Epitaxial BiFeO3.