Ultra-fast terahertz spectroscopy in giant magneto resistive systems Terahertz-spectroscopy allows the measurement of basic factors of magneto transport – the basis of progressive nano-electronics.
The future technology of spintronics now has a new, highly effective instrument research tool: Physicians from Mainz and Berlin have implemented ultra-fast terahertz-spectroscopy to investigate elemental properties of spintronic components – and it’s been a success.
“This gives us direct access to the absolutely fundamental elements of magneto transport,” explained Prof. Dr. Mathias Kläui of the Institute of Physics from the Johannes Gutenberg University of Mainz (JGU). Spinotronics not only use the charge of the electrons for processing information, but also their spin, the magnetic moment of the electrons. Spintronics are already in use in hard drive reading heads and sensors, for instance in the automotive industry, and offer a great potential for non-volatile memories.
One thing that is fundamental to many spintronics applications is the giant magneto resistive or GMR effect discovered in the 1990s. Its discoverers, Albert Fert and Peter Grünberg were given the Nobel Prize in Physics for this in 2007. The GMR effect functions like a type of magnetic sensor, changing its resistance depending on the magnetic orientation of the individual thin layers of material. This results in the dispersion of electrons, whose impact can be seen in the resistance but which had previously not been able to be precisely determined with conventional experimental methods. The difficulty primarily lies in the extremely short timeframes in which the effects take place. The results of the dispersion of electrons occurs on a time scale of less than 100 femtoseconds, a femtosecond being a quadrillionth of a second.
In cooperation with the working groups of Mathias Kläui at the JGU and Dmitry Turchinovich at the Max Planck Institute for Polymer Research in Mainz (MPIP), where the researchers for the Mainz branch of the Sensitec GmbH company were also involved, and of the Fritz-Haber Institute of the Max Planck society in Berlin, the challenge was solved with the help of terahertz spectroscopy, also referred to as submillimeter wave spectroscopy. The scientists were able to observe the magneto transport in a ferromagnetic structure directly using this method and they could determine the relevant parameters precisely and clearly: the spin-dependent charge carrier density and the spin-dependent dispersion rates of the conducting electrons.
“Terahertz spectroscopy is often used for material inspections. We have now shown that this method can also be used for magneto transport," says Prof. Dr. Dmitry Turchinovich, Head of the Research group for "Ultrafast Dynamics and Terahertz Spectroscopy” at the MPIP and as a member of the Graduate School of Excellence in Material Science in Mainz (MAINZ). "In doing so, we experimentally confirmed what is known as the Mott model of 1936, which describes electron transport in ferromagnetic metals, for the first time."
This link takes you to the publication on Nature Physics (doi:10.1038/nphys3384)