By studying Cr-doped (Sb, Bi)2Te3 thin films, researchers have identified the components needed to develop electric devices that consume extremely low levels of power, reporting their findings in the journal Nature Communications.
At low temperatures, the film experiences the flow of an electric current around its edges without losing energy, even without an external magnetic field. The attraction present is attributed to the ferromagnetic properties the material has, although it is not clear how it managed to gain such.
For the first time, however, researchers reveal the reason why the ferromagnetic properties manifest, in hopes of creating unique materials that can be used at room temperature. Practical applications were not pursued before because for an electric current to flow without losing energy, extremely low temperature and a large external magnetic field have to be present.
To address the problem, researchers believed that creating topological insulators with ferromagnetic properties will be key, and they were right. A topological insulator is neither an insulator nor a metal and features exotic properties, such as generating electric currents on its surface or edge without generating any inside.
As chromium (Cr) is a magnetic element, its atom is representative of a magnet the size of an atom. North-south orientations of atom-sized magnets have the tendency to align in parallel when Cr atoms interact, and when they do, this results in the Cr-doped (Sb, Bi)2Te3 film's ferromagnetism.
Still, the researchers pointed out that interatomic distances between chromium atoms are too long for interactions to be sufficient enough to produce ferromagnetism. It turns out that that atoms from the non-magnetic elements such as selenium and tellurium are the ones that mediate between magnetic interactions in chromium atoms, acting as the bond stabilizing north-south orientations so that they face just one direction.
Experiments for the study were mostly conducted at SPring-8, a synchrotron radiation facility situated in Japan's Hyogo Prefecture. The facility was developed by the Japan Atomic Energy Research Institute and RIKEN, Japan's largest comprehensive research institute.
"We would not have achieved perfect results without the facilities and staff there," said Akio Kimura, a Hiroshima University professor and one of the members of the research group. "I greatly appreciate their efforts."
The research was supported by the Ministry of Science and Technology of China, the Natural Science Foundation of China, JSPS KAKENHI and the Helmholtz Association. Other members of the group include: Mao Ye, Xiaoming Xie, Wei Li, Shan Qiao, Siyuan Zhu, Dawei Shen, Yukiharu Takeda, Zhengtai Liu, Yuji Saitoh, Haifeng Yang, Jiajia Wang, Zhen Liu, Hong Pan, Fuhao Ji, Munisa Nurmamat and Kazuki Sumida.
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