Miscellaneous

Watching the first steps of magnetic information transport

Thursday, 13th September 2018Miscellaneous

In conventional electronics, information is encoded in bits (0 or 1) by the presence or absence of electron charges. A promising new approach—spintronics—aims to use the electron ‘spin’ as an information carrier. This method takes advantage of the orientation (up or down) of the electron spin to encode information. The speed at which electronics operate continues to increase and is expected to work at terahertz speeds in the future. To be competitive and compatible with charge-based electronics, spintronic operations must, therefore, also work at these high frequencies.

An elementary but vital spintronic operation is the transport of spin-based information from a magnetic metal layer into an attached nonmagnetic metal layer (see figure). It was discovered only a few years ago that this transfer can happen simply by heating the magnet and metal to different temperatures. When heating the magnetic layer, hot electrons move into the colder nonmagnetic metal, thereby carrying magnetic information across the interface of the two layers.

What is remarkable is that this transfer still occurs when the magnetic layer is an electrical insulator—meaning electron currents cannot move across the interface. The spin transfer happens instead from the torque exerted by the immobile spins of the magnetic layer onto the spins of the neighbouring mobile electrons in the metal layer. This phenomenon is called the spin Seebeck effect.

In the framework of the CRC/TRR 227 at the Freie Universität Berlin, a team of scientists from Germany, England and Japan aimed to discover just how quickly the spin transfer can happen. “Answering this question is not only interesting for potential applications in future high-speed information technology. It is also relevant to understand the elementary steps that lead to the emergence of the spin current”, says physicist Dr. Tom Seifert, who conducted the experiments at the Fritz Haber Institute of the Max Planck Society in Berlin.

In their experiment, the researchers used a pulse from a femtosecond laser to heat up a metal film on top of a magnetic insulator in less than one millionth of a millionth of a second (see figure). The metal itself then emitted an electromagnetic pulse caused by the spin current flowing into it—behaving like an ultrafast spin-amperemeter. Using the emitted pulse, the researchers observed the formation of the spin current caused by the spin Seebeck effect. Once heated, the electrons in the metal hit the metal-insulator interface and are reflected back. During this scattering event, the magnet exerts torque on the incident electron’s spin, aligning it a little more parallel to the magnetization M of the insulator. Thus, spin information of the magnetic insulator is transported into the metal (see figure at time 0 femtoseconds).

The researchers made a surprising observation—the spin transport does not begin immediately, taking about 200 femtoseconds to peak. The reason is that the laser pulse excites relatively few electrons, but they receive a lot of energy and collide with ‘cold’ electrons, redistributing the energy. This avalanche-like process heats up a large number of electrons which also hit the interface, becoming a part of the spin transport (see figure at time 100 femtoseconds). “The photoexcited electrons need to multiply their numbers to generate sizeable spin transport”, says theorist Dr. Joseph Barker, who conducted simulations of the spin dynamics at the Tohoku University in Sendai, Japan.

Press contacts:
Prof. Tobias Kampfrath, Freie Universität Berlin and Fritz Haber Institute of the Max Planck Society, Berlin, +49 30 8413-5222, tobias.kampfrath@fu-berlin.de

Original publication:
T. Seifert, S. Jaiswal, J. Barker, S.T. Weber, I. Razdolski, J. Cramer, O. Gueckstock, S. Maehrlein, L. Nadvornik, S. Watanabe, C. Ciccarelli, A. Melnikov, G. Jakob, M. Münzenberg, S.T.B. Goennenwein, G. Woltersdorf, B. Rethfeld, P.W. Brouwer, M. Wolf, M. Kläui, T. Kampfrath
Femtosecond formation dynamics of the spin Seebeck effect revealed by terahertz spectroscopy
Nature Communications 9, Article number: 2899 (2018)   

Figure: Watching the ultrafast spin Seebeck effect. At time 0 femtoseconds, a bilayer made of a magnetic insulator (with magnetization M) and a nonmagnetic metallic layer is heated by an extremely short ultrafast laser pulse. The resulting transport of spin from the magnet to the metal leads to the emission of a terahertz pulse whose measurement allows the researchers to monitor the dynamics of the excited metal electrons with an extremely fine time resolution of 20 femtoseconds. Their work reveals that the strength of the spin transfer is directly proportional to the number of heated metal electrons, which is maximal at about 100 femtoseconds after laser excitation. After about 1000 femtoseconds, the excited metal electrons have cooled down and transferred their excess energy to the atomic lattice.

Figure: Watching the ultrafast spin Seebeck effect. At time 0 femtoseconds, a bilayer made of a magnetic insulator (with magnetization M) and a nonmagnetic metallic layer is heated by an extremely short ultrafast laser pulse. The resulting transport of spin from the magnet to the metal leads to the emission of a terahertz pulse whose measurement allows the researchers to monitor the dynamics of the excited metal electrons with an extremely fine time resolution of 20 femtoseconds. Their work reveals that the strength of the spin transfer is directly proportional to the number of heated metal electrons, which is maximal at about 100 femtoseconds after laser excitation. After about 1000 femtoseconds, the excited metal electrons have cooled down and transferred their excess energy to the atomic lattice.


John B. Fenn Award for a Distinguished Contribution in Mass Spectrometry for Gert von Helden

Wednesday, 2nd May 2018Miscellaneous
Gert von Helden receives, together with Martin Jarrold and David Clemmer (both Indiana University, USA), the 2018 “John B. Fenn Award for a Distinguished Contribution in Mass Spectrometry” by the American Society for Mass Spectrometry (ASMS). The Award recognizes a focused or singular achievement in fundamental or applied mass spectrometry and is given for pioneering contributions to the development of ion mobility spectrometry (IMS).
See:  https://www.asms.org/about-asms-awards/distinguished-contribution

 


A comprehensive volume on chemical warfare entitled “One Hundred Years of Chemical Warfare: Research, Deployment, Consequences” has been published under the auspices of the Max Planck Society

Wednesday, 6th December 2017Publication highlights, Miscellaneous

ProductFlyer-9783319516639On April 22, 1915, the German military released 150 tons of chlorine gas at Ypres, Belgium. Carried by a long-awaited wind, the chlorine cloud passed within a few minutes through the British and French trenches, leaving behind at least 1,000 dead and 4,000 injured. This chemical attack, which amounted to the first use of a weapon of mass destruction, marks a turning point in world history. The preparation as well as the execution of the gas attack was orchestrated by Fritz Haber, the director of the Kaiser Wilhelm Institute for Physical Chemistry and Electrochemistry in Berlin-Dahlem. During World War I, Haber transformed his research institute into a center for the development of chemical weapons (and of the means of protection against them).

Bretislav Friedrich and Martin Wolf (Fritz Haber Institute of the Max Planck Society, the successor institution of Haber’s institute) together with Dieter Hoffmann, Jürgen Renn, and Florian Schmaltz (Max Planck Institute for the History of Science) organized an international symposium to commemorate the centenary of the infamous chemical attack. The symposium examined crucial facets of chemical warfare from the first research on and deployment of chemical weapons in WWI to the development and use of chemical warfare during the century hence. The focus was on scientific, ethical, legal, and political issues of chemical weapons research and deployment — including the issue of dual use — as well as the ongoing effort to control the possession of chemical weapons and to ultimately achieve their elimination.

The volume consists of papers presented at the symposium and supplemented by additional articles that together cover key aspects of chemical warfare from 22 April 1915 until the summer of 2015.

The book was presented at a symposium on November 30, 2017 to the delegates of the 22nd Conference of State Parties of the Chemical Weapons Convention at the Organization for the Prohibition of Chemical Weapons in The Hague. Introduced by Paul Walker (Green Cross) and presented and moderated by Bretislav Friedrich (FHI), the symposium entitled “One Hundred Years since Ypres and Counting: Glimpses of the Past and the Present” explained the involvement of the Max Planck Society and provided a sampling of the book’s chapters by Edward Spiers (University of Leeds), Ulf Schmidt (University of Kent), Karin Mlodoch (Haukari), and Ralf Trapp (Chessenaz). Among the attendees were four survivors of the 1988 Halabja chemical attack.

Website: http://www.springer.com/de/book/9783319516639
eBook available at https://link.springer.com/book/10.1007/978-3-319-51664-6


(Deutsch) Azubipreis für Robert Hippmann Pena

Tuesday, 5th September 2017Miscellaneous

Sorry, this entry is only available in German.


Free-electron laser allows scientists to observe a molecular ball bearing

Tuesday, 3rd January 2017Miscellaneous
Graduate students Matias Fagiani (left) and Sreekanta Debnath (right) in front of the undulator of the free-electron laser at the Fritz Haber Institute.

Graduate students Matias Fagiani (left) and Sreekanta Debnath (right) in front of the undulator of the free-electron laser at the Fritz Haber Institute.

The free-electron laser (FEL) at the Fritz Haber Institute (FHI) generates intense pulses of infrared radiation of widely tunable wavelength. Unlike conventional lasers, where the radiation is produced in a gas, liquid, or solid, in an FEL it is generated by an electron beam propagating freely through a vacuum tube. In a device called undulator (Fig. 1),strong magnetic fields of alternating polarity force the electrons on a wiggling (undulating) motion, thereby causing the emission of radiation. The radiation wavelength can be tuned simply by varying the electron energy or the magnetic field strength. Before entering the undulator, however, the electrons need to be accelerated to almost the speed of light, requiring a complex electron accelerator. Since 2013 such an installation has been operational at the Fritz Haber Institute.

In collaboration with scientists from the Wilhelm Ostwald Institute for Physical und Theoretical Chemistry (Leipzig University) and from the Institute for Optics und Atomic Physics (Technical University Berlin) the FEL radiation has been applied to investigate a very special molecular system, the boron cluster B13+. It was known previously that 13 boron atoms can form a highly stable compound, referred to as a magic cluster. It is a planar system composed of two concentric rings; an inner B3-ring and an outer B10-ring (see Fig. 2). The key feature is that the system is very stable but not rigid. Previously, Thomas Heine (Theoretical Chemistry, Leipzig) and his coworkers predicted that it is possible for the rings to rotate like a ball bearing with no detrimental effect on the stability of the system. Pairs of electrons serve as the bearing’s balls, enabling the inner and outer rings to counter rotate effectively free of friction.titelbild_en_png

The group of Knut Asmis (Physical Chemistry, Leipzig), jointly with André Fielicke (TU Berlin), succeeded to prepare a single-isotope form of this very special boron system. And application of the FHI FEL radiation provided evidence for its concentric ring structure and also for the predicted rotational motion. The intense and tunable IR radiation from the FEL made it possible to measure the vibrational spectrum of B13+, revealing a fingerprint of the possible motions within the cluster. The spectrum exhibits clear evidence for the quasi rotation of the two rings.

Wieland Schöllkopf, who is heading the FHI FEL facility, points out that these results could not have been achieved with a conventional laser source. Hence, it represents another impressive example of possible applications of FEL radiation. Furthermore, demonstrating a molecular ball bearing consisting of just 13 atoms presents another example from the young and exciting research field of “Molecular Machines”, the development of which was just awarded by the 2016 Nobel Prize in Chemistry.

Publication:

Structure and Fluxionality of B13+ Probed by Infrared Photodissociation Spectroscopy
M.R. Fagiani, X. Song, P. Petkov, S. Debnath, S. Gewinner, W. Schöllkopf, T. Heine, A. Fielicke, K.R. Asmis
Angew. Chem. Int. Ed., 56, 501–504, (2017)


(Deutsch) EMIL am Synchrotron BESSY II eingeweiht

Tuesday, 8th November 2016Miscellaneous

Sorry, this entry is only available in German.


Hans-Joachim Freund elected to American Academy of Arts and Sciences

Friday, 29th April 2016Miscellaneous

CAMBRIDGE, MA | APRIL 20, 2016 – The American Academy of Arts and Sciences today announced the election of 213 new members. They include some of the world’s most accomplished scholars, scientists, writers, artists, as well as civic, business, and philanthropic leaders. Among those elected into this newest class is Professor Dr. Hans-Joachim Freund of Fritz-Haber-Institut der Max-Planck-Gesellschaft. […]

Founded in 1780, the American Academy of Arts and Sciences is one of the country’s oldest learned societies and independent policy research centers, convening leaders from the academic, business, and government sectors to respond to the challenges facing—and opportunities available to—the nation and the world. Current Academy research focuses on higher education, the humanities, and the arts; science and technology policy; global security and energy; and American institutions and the public good. The Academy’s work is advanced by its elected members, who are leaders in the academic disciplines, the arts, business, and public affairs from around the world.

(Text taken from the AAAS)


Observing basic interactions in solids

Friday, 15th April 2016Miscellaneous
Illustration of the femtosecond electron diffraction experiment. Electrons diffracting off a crystalline lattice reveal information of the atomic vibrations in the crystal. Using extremely short pulses of electrons arriving at a defined time after the sample was excited with a femtosecond laser pulse, a movie of the energy transfer between the electrons and the atomic motion in the material is obtained. copyright: Waldecker/FHI

Illustration of the femtosecond electron diffraction experiment. Electrons diffracting off a crystalline lattice reveal information of the atomic vibrations in the crystal. Using extremely short pulses of electrons arriving at a defined time after the sample was excited with a femtosecond laser pulse, a movie of the energy transfer between the electrons and the atomic motion in the material is obtained.
copyright: Waldecker/FHI

Interactions between electrons and vibrations of atomic ions, of which all condensed matter is composed, and which determine such fundamental features like electron and thermal conductivity of materials, energy dissipation in electronic devices, and emergence of quantum phenomena like superconductivity, are a central subject in solid-state physics.

Lutz Waldecker and Roman Bertoni of the Max Planck Research Group headed by Ralph Ernstorfer, in cooperation with Jan Vorberger of the Max-Planck-Institut für Physik komplexer Systeme, Dresden, have now visualized and quantified electron-lattice interactions after a sudden very short external disturbance (a 50 femtosecond infrared laser pulse) in aluminum, a proto-typical metal. Due to these interactions, the excited electrons proceed to equilibrate with the atomic vibrations, and successive snapshots of the latter provide a “movie” of the relaxation process. Comparing the experimental findings with state-of-the-art numerical calculations of atomic mean squared displacements made it possible to revise the existing model of such interactions.

Original publication:
Lutz Waldecker, Roman Bertoni, Ralph Ernstorfer, and Jan Vorberger
Electron-Phonon Coupling and Energy Flow in a Simple Metal beyond the Two-Temperature Approximation
Physical Review X vol. 6 (doi: 10.1103/PhysRevX.6.021003)

Contact persons: Dr. Ralph Ernstorfer, Lutz Waldecker

Gaede-Preis 2016 is awarded to Dr. Julia Stähler and Gerhard Ertl Young Investigator Award for Dr. Takashi Kumagai

Tuesday, 5th April 2016Miscellaneous

We are happy to announce that the Deutsche Vakuumgesellschaft (DVG) awarded the Gaede-Preis 2016 to Dr. Julia Stähler (Department od Physical Chemistry) in recognition of her outstanding work on ultrafast dynamics of elementary processes and many-body effects at surfaces and in solids. The prize was handed over on March 8, 2016 in a Special Ceremonial Session at the 80th Annual Meeting of the DPG in Regensburg.

At the DPG (The Surface Science Division of the Deutsche Physikalische Gesellschaft) Spring meeting, the winner for the 2016 Gerhard Ertl Young Investigator Award was chosen: Dr. Takashi Kumagai (also from the Department of Physical Chemistry).

Congratulations to our colleagues!


Better adhesion than previously thought in van der Waals force

Friday, 18th March 2016Miscellaneous
Because they are describing the van der Waals force as an interaction between waves rather than between particles, researchers, including those at the Fritz Haber Institute, have established that the forces of attraction between uncharged atoms and molecules extend considerably further than was previously assumed. The understanding of the forces that operate between nanostructures like individual sheets of graphene, proteins and carbon nanotubes is thus changing. © Fritz-Haber-Institut der MPG

Because they are describing the van der Waals force as an interaction between waves rather than between particles, researchers, including those at the Fritz Haber Institute, have established that the forces of attraction between uncharged atoms and molecules extend considerably further than was previously assumed. The understanding of the forces that operate between nanostructures like individual sheets of graphene, proteins and carbon nanotubes is thus changing.
© Fritz-Haber-Institut der MPG

“The quantum mechanical description of the force between uncharged atoms and molecules demonstrated in real structures

They ensure that gases below a certain temperature condense into liquids. They give glue its adhesive force and enable geckos to hang upside down on a wall. The ‘they’ in question: van der Waals forces. Researchers at the Berlin-based Fritz Haber Institute of the Max Planck Society, together with colleagues in Italy and the USA, have succeeded in describing, more accurately than they were previously able to, the forces of attraction that operate between uncharged nanostructures. For the first time ever, they have successfully applied the concept to real molecular structures. The researchers can now envisage that practice-oriented material scientists, process designers and even drug researchers will one day benefit from the better understanding of van der Waals forces. It could, for example, then be possible to systematically modulate the forces.”

Go on to the full press release of the Max Planck Society.

Alberto Ambrosetti, Nicola Ferri, Robert A. DiStasio Jr. and Alexandre Tkatchenko
Wavelike Charge Density Fluctuations and van der Waals Interactions at the Nanoscale