Ultrafast terahertz spectroscopy yields direct insight into the building block of modern magnetic memories
Modern magnetic memories, such as hard drives installed in almost every computer, can store a very large amount of information thanks to very tiny, nanoscale magnetic sensors used for memory readout. The operation of these magnetic sensors, called the spin-valves, is based on the effect of giant magnetoresistance (GMR), for which its inventors Albert Fert and Peter Grünberg were awarded a Nobel Prize in Physics in 2007.
The GMR effect is based on the idea of electrical conduction in ferromagnetic metals, proposed by Sir Nevill F. Mott as early as in 1936. In Mott’s picture, the conduction electrons in ferromagnetic metals experience scattering depending on their microscopic magnetic moment – the spin.
That is, the electrons with one spin orientation scatter less and are therefore more conductive than the electrons with the opposite spin orientation. This spin-asymmetry in electron conduction is greatly amplified when the thin films of ferromagnetic and nonmagnetic metals are combined together to form a spin-valve in which electrical resistivity becomes very sensitive to the magnetic field, leading to a GMR effect.
Even though the Mott spin-dependent conductivity is at the heart of magnetic memories and many other technologies, its direct observation has been a long time challenge. Indeed the fundamental parameters of Mott conduction – spin-dependent electron scattering time and spin-dependent electron density – can be directly and unambiguously determined only if the conductivity of the metal is measured on the same ultrafast timescale at which the electron scattering occurs, that is sub-100 femtosecond (1 fs = 10-15 s, i.e. one millionth of one billionth of a second). For many decades, such an extremely fast timescale of experimental measurement precluded the observation of magnetotransport in metals on the fundamental level.
In a collaborative work carried out by the research groups at the Max Planck Institute for Polymer Research (MPI-P) and the Johannes Gutenberg University (JGU), with the contribution of Sensitec GmbH and the Fritz Haber Institute of the Max Planck Society, the scientists managed to break the speed barrier for fundamental magnetotransport measurements by using a method called ultrafast terahertz spectroscopy (1 THz = 1012 Hz, i.e. one thousand billion oscillations per second).
“By studying the interaction of THz electromagnetic waves - which oscillate about as fast as the electrons in metal scatter their momentum - with a spin-valve, we could directly measure for the first time the fundamental parameters of Mott conduction”, explains Dmitry Turchinovich, project leader at the MPI-P. “In particular, we found that the traditional measurements performed on the slower timescales significantly underestimate the spin-asymmetry in electron scattering which is responsible for the magnetic sensor operation”.
The results of the research team: Zuanming Jin, Alexander Tkach, Frederick Casper, Victor Spetter, Hubert Grimm, Andy Thomas, Tobias Kampfrath, and Mischa Bonn, led by Dmitry Turchinovich (MPI-P) and Mathias Kläui (JGU) have recently been published in Nature Physics.
This work adds a new and powerful tool, ultrafast THz spectroscopy, to the studies in spintronics, opening up a new research field – terahertz spintronics.
Natacha Bouvier | Max-Planck-Institut für Polymerforschung
Enhancing the quantum sensing capabilities of diamond
23.11.2017 | The Hebrew University of Jerusalem
Quantum optics allows us to abandon expensive lasers in spectroscopy
22.11.2017 | Lomonosov Moscow State University
Heat from the friction of rocks caused by tidal forces could be the “engine” for the hydrothermal activity on Saturn's moon Enceladus. This presupposes that...
The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.
Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
23.11.2017 | Information Technology
23.11.2017 | Physics and Astronomy
23.11.2017 | Life Sciences