Brilliant composition for half-metal alloys

Half-metals are unique magnetic compounds that have been attracting interest in the development of mass-storage technologies. Some of the materials in the family of Heusler alloys were predicted to have a half-metallic nature, but their half-metallic electronic structure varies with their composition ratio and atomic ordered structure.

One property, spin polarisation, is fundamental to the material’s half-metallic properties. Spin polarisation ratio is a physical property that indicates how polarised the number of electrons with spin in the up and down directions is. Because spin polarisation is influenced by the elemental composition of the Heusler alloy, it’s important to characterise and optimise the atomic composition of Heusler alloys to achieve the highest spin polarisation. But current methods for determining the spin polarisation of half-metals are either time-consuming or only provide an indirect measure.

A team of researchers from Japan, led by Yuya Sakuraba of the National Institute for Materials Science (NIMS), has developed a method to quickly determine the spin polarisation of Heusler alloys, using high-brilliance synchrotron radiation. With this approach, they were able to rapidly identify the ideal composition of elements to achieve the highest spin polarisation. Their findings were published in the journal Science and Technology of Advanced Materials.

The Heusler alloy in question was a mix of cobalt, manganese, and silicon. The research team created composition-spread thin films of the alloy, varying the proportion of manganese from 10% to 40% along the length of the sample.

They then bombarded the film with extremely bright radiation at the NanoTerasu synchrotron facility, which opened in April 2024. This bombardment revealed that the ideal composition to maximise spin polarisation in the alloy was for manganese to make up 27% of the alloy’s atomic weight. 

Did you know?

The accelerated electrons at NanoTerasu are a billion times brighter than sunlight, enabling observations down to one nanometre. In comparison, human hair is 100,000 nanometres thick.

Terasu means to shine in Japanese, similar to Amaterasu, the sun-god who illuminated the world. NanoTerasu holds the record for the world's highest energy resolution and is located at Sendai, Japan. 

This experiment marked the first successful application of photoelectron spectroscopy at the NanoTerasu facility. The experiment was done in a single day — much faster than existing methods of determining spin polarisation.

“The findings address a critical challenge in materials science by drastically reducing the time required to evaluate and optimise spin polarisation in half-metallic materials,” Sakuraba says.

This study paves the way for wider application of the technique not just to half-metallic materials but a variety of other magnetic and spintronic materials. “The rapid, efficient method presented in this study could significantly impact the development of next-generation technologies, such as high-capacity hard disk drives and advanced spintronic devices,” says Sakuraba.

Read the paper

Science and Technology of Advanced Materials: https://doi.org/10.1080/14686996.2024.2439781 

Further information 

Prof Yuya Sakuraba
[email protected]
National Institute for Materials Science (NIMS) 

STAM Inquiries 
[email protected] 
STAM Editorial Office 

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