Ultrafast electrons in magnetic oxides: A new direction for spintronics?


Date:
August 19, 2020
Source:
Martin-Luther-Universita"t Halle-Wittenberg
Summary:
Special metal oxides could one day replace semiconductor materials
that are commonly used today in processors. Now, for the first
time, researchers were able to observe how electronic charge
excitation changes electron spin in metal oxides in an ultrafast
and inphase manner.



FULL STORY ========================================================================== Special metal oxides could one day replace semiconductor materials
that are commonly used today in processors. Now, for the first time,
an international team of researchers from Martin Luther University Halle-Wittenberg (MLU), the University of Kaiserslautern and the
University of Fribourg in Switzerland was able to observe how electronic
charge excitation changes electron spin in metal oxides in an ultrafast
and inphase manner. The study was published in the journal Nature Communications.


==========================================================================
In modern semiconductor electronics, the first key step in every
transistor is to lift electrons over the so-called band gap in the semiconductor. Electrons have to move through a material that is,
in actual fact, 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," explains
Professor Wolf Widdra from the Institute of Physics at MLU.

Spintronics attempts to solve this problem with the help of so-called
spin.

This is the intrinsic angular momentum of an electron that produces
the magnetic moment, thereby generating the magnetism that is used in information processing. The coupling of electronic and magnetic properties determines the functionality. "Magnetic oxides are an important class of materials for spintronics because they don't transfer electron current,
only magnetic information," says Widdra, who led the study as part of the
joint Collaborative Research Centre CRC/TRR 227 "Ultrafast Spin Dynamics"
at MLU and Freie Universita"t Berlin. Until recently, however, it hadn't
been clear how the electron transfer across the band gap coupled with
the spin of the magnetic oxide. The team has now successfully observed
this process and has developed a new theory for it. Groups of theoretical
and experimental physicists joined forces to tackle this issue.

Using a state-of-the-art, ultra-short pulse laser, the researchers were
able to excite an electron to lift it across the band gap in nickel
oxide. They also observed how the information was then transferred to the magnetic system. This enabled the team to identify a previously unknown ultrafast coupling mechanism that occurs on a femtosecond scale, i.e. a 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," adds Widdra.

According to the physicist, the findings now pave the way for ultrafast spintronics. This should facilitate the development of new ultra-fast
storage systems and information technologies in the future.

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


========================================================================== Story Source: Materials provided by Martin-Luther-Universita"t_Halle-Wittenberg. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Konrad Gillmeister, Denis Golež, Cheng-Tien Chiang, Nikolaj
Bittner,
Yaroslav Pavlyukh, Jamal Berakdar, Philipp Werner, Wolf
Widdra. Ultrafast coupled charge and spin dynamics in strongly
correlated NiO. Nature Communications, 2020; 11 (1) DOI:
10.1038/s41467-020-17925-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200819102813.htm

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