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New Study on Metal Oxide Electron Spin Could Pave Way for Ultrafast Spintronics

Someday special metal oxides could serve as alternatives to semiconductor materials that are more common in existing processors.

For the first time, an international group of scientists from Martin Luther University Halle-Wittenberg (MLU), the University of Kaiserslautern, and the University of Fribourg in Switzerland has now been able to visualize how excitation through electronic charge modifies electron spin in metal oxides in an in-phase and ultrafast way.

The research has been reported in the Nature Communications journal.

In every transistor of modern semiconductor electronics, the first important step is to lift electrons over what is called the bandgap in the semiconductor. It is essential for electrons to move through a material that is non-conductive.

After they have been excited across the band gap, the moving electric charges of the electrons generate the currents that are used in information processing. These currents can cause processors to become hot, leading to energy loss.

Wolf Widdra, Professor, Institute of Physics, Martin Luther University Halle-Wittenberg

The field of spintronics would try to find a solution to this problem by using what is called the spin. This is an electron’s intrinsic angular momentum that generates the magnetic moment, producing the magnetism used in information processing. The functionality is governed by the coupling of magnetic and electronic properties.

Magnetic oxides are an important class of materials for spintronics because they don’t transfer electron current, only magnetic information.

Wolf Widdra, Professor, Institute of Physics, Martin Luther University Halle-Wittenberg

Professor Widdra headed the study as part of the joint Collaborative Research Centre CRC/TRR 227 “Ultrafast Spin Dynamics” at MLU and Freie Universität Berlin.

However, so far, it had not been evident how the transfer of electrons across the bandgap coupled with the magnetic oxide’s spin. Now, the researchers have successfully visualized this process and have proposed a new theory to explain it. To address this problem, various teams of experimental and theoretical physicists collaborated.

The researchers successfully used a sophisticated, ultra-short pulse laser to excite an electron and lift it through the bandgap in nickel oxide. In addition, they were able to observe the subsequent transfer of information to the magnetic system.

Therefore, researchers could find a previously obscure ultrafast coupling mechanism that takes place on a femtosecond scale, where one femtosecond is equal to one-quadrillionth of a second.

The complex many-body properties generated through the excitation of the electron by the laser have revealed this surprising observation but also made us think long and hard about how to interpret it correctly.

Wolf Widdra, Professor, Institute of Physics, Martin Luther University Halle-Wittenberg

The physicist added that the results of the study now open the door for ultrafast spintronics. This should enable the designing of innovative, ultra-fast storage systems and information technologies in the days to come.

The research was financially supported by the Deutsche Forschungsgemeinschaft (German Research Foundation, DFG), the Swiss National Science Foundation, and the European Research Council.

Journal Reference:

Gillmeister, K., et al. (2020) Ultrafast coupled charge and spin dynamics in strongly correlated NiO. Nature Communications.


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