Stable and moveable; is hexagonal boron nitride the universal foundation?

Osaka, Japan – Magnetite is a type of iron oxide with the chemical formula Fe₃O₄. It has many interesting properties that make it the focus of research for use in spintronics devices. Researchers from Osaka University have shown that Fe₃O₄ thin films can be grown on a hexagonal boron nitride (hBN) substrate, meaning the films can be easily transferred into different systems. Their findings were published in ACS Applied Electronic Materials.

We are constantly learning more about the properties of materials. Sophisticated details of the electronic and magnetic properties of metal oxides—such as Fe₃O₄—can be harnessed to optimize complex systems such as disk drives and sensing devices.

The behavior of the electrons in Fe₃O₄ gives it distinctive properties. For example, it changes from being an insulator to conducting electric charge at a specific, very low temperature and loses its magnetic properties at the high temperature of 578°C. These properties can be used to tune devices for specific applications.

Growing high-quality thin films of Fe₃O₄ is therefore important and has been achieved on a variety of stiff substrates. However, achieving flexible devices is regarded as an important goal in the development of electronics, and this requires films that can be easily transferred onto flexible substrates.

hBN is a physically and chemically stable material, making it an excellent choice for growing Fe₃O₄ films. hBN has layers that associate through der Waals interactions, which are weaker than ionic and covalent bonds, making them easier to manipulate and move.

“Generally, if you grow crystals of one material on another crystal, the way their atoms are arranged has to match or the film will grow with defects,” explains study first author Shingo Genchi. “However, owing to the van der Waals interactions of hBN, high-quality Fe₃O₄ could be grown despite there being a mismatch, showing the potential of hBN as a universal transferrable substrate.”

The properties of the Fe₃O₄ film grown on hBN were investigated, and it was found that the transition temperature from an insulating to metallic material was not affected by hBN. The temperature of the change was also found to be the same for Fe₃O₄ films with different thicknesses.

The film was transferred onto a SiO₂/Si substrate and again retained its properties, demonstrating the versatility of the hBN approach.

“Our high-quality Fe₃O₄ films are an exciting next step in the development of spintronic materials,” says study corresponding author Hidekazu Tanaka. “We believe that our films will make an important contribution to flexible devices.”

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The article, “Prominent Verway transition of Fe₃O₄ thin films grown on transferable hexagonal boron nitride,” was published in ACS Applied Electronic Materials at DOI: https://doi.org/10.1021/acsaelm.1c00803

About Osaka University

Osaka University was founded in 1931 as one of the seven imperial universities of Japan and is now one of Japan's leading comprehensive universities with a broad disciplinary spectrum. This strength is coupled with a singular drive for innovation that extends throughout the scientific process, from fundamental research to the creation of applied technology with positive economic impacts. Its commitment to innovation has been recognized in Japan and around the world, being named Japan's most innovative university in 2015 (Reuters 2015 Top 100) and one of the most innovative institutions in the world in 2017 (Innovative Universities and the Nature Index Innovation 2017). Now, Osaka University is leveraging its role as a Designated National University Corporation selected by the Ministry of Education, Culture, Sports, Science and Technology to contribute to innovation for human welfare, sustainable development of society, and social transformation.

Website: https://resou.osaka-u.ac.jp/en