Magnetic semiconductor opens up silicon-based spintronics

The researchers from North Carolina State University synthesised the new compound, strontium tin oxide (Sr₃SnO), as an epitaxial thin film on a silicon chip. Because Sr₃SnO is a dilute magnetic semiconductor (a material exhibiting ferromagnetism and semiconductor properties), it could be used to create transistors that operate at room temperature based on magnetic fields.

‘We’re talking about cool transistors for use in spintronics,’ said Dr. Jay Narayan, John C. Fan Distinguished Professor of Materials Science and Engineering at NC State and senior author of a paper describing the work. ‘Spintronics’ refers to technologies used in solid-state devices that take advantage of the inherent ‘spin’ in electrons and their related magnetic momentum.

‘There are other materials that are dilute magnetic semiconductors, but researchers have struggled to integrate those materials on a silicon substrate, which is essential for their use in multifunctional, smart devices,’ Narayan said in a statement. ‘We were able to synthesise this material as a single crystal on a silicon chip.’

‘This moves us closer to developing spin-based devices, or spintronics,’ said Dr Justin Schwartz, co-author of the paper, Kobe Steel Distinguished Professor and Department Head of the Materials Science and Engineering Department at NC State. ‘And learning that this material has magnetic semiconductor properties was a happy surprise.’

The researchers had set out to create a material that would be a topological insulator. In topological insulators the bulk of the material serves as an electrical insulator, but the surface can act as a highly conductive material – and these properties are not easily affected or destroyed by defects in the material. In effect, that means that a topological insulator material can be a conductor and its own insulator at the same time.

Two materials are known to be topological insulators – bismuth telluride and bismuth selenide but it has been predicted that other materials may also have topological insulator properties. Sr3SnO is one of those theoretical materials, which is why the researchers synthesised it. However, while early tests are promising, the researchers are still testing the Sr3SnO to confirm whether it has all the characteristics of a topological insulator.

The paper, ‘Epitaxial integration of dilute magnetic semiconductor Sr₃SnO with Si (001),’ was published on September 9 in Applied Physics Letters.