Scientific Highlights 2013

9. July 2013

Single Domain Spin Manipulation by Electric Fields in Strain Coupled Artificial Multiferroic Nanostructures

Encoding information by the application of an electric field has a key role in the development of novel memory devices that can operate at high speed while keeping low energy consumption. In magnetoelectric multiferroics, magnetic and ferroelectric ordering coexist and are coupled together so that it is possible to manipulate the material's magnetic structure by applying an electric field with a negligible current flow. These materials however are rare, and up to now showed ordering temperatures well below room temperature which prevent their future implementation in real world devices. To overcome this problem, it is possible to artificially couple a ferromagnetic and ferromagnetic material to create an artificial multiferroic. A team of researchers at the Swiss Light Source (PSI), Laboratory for Micro and Nanotechnology (PSI) and University of California (UCLA) has investigated the possibility of achieving giant magnetoelectric coupling in strain-coupled artificial multiferroic nanostructures. Ferromagnetic nanoislands made out of nickel were grown on a piezoelectric ferroelectric crystal (PMN-PT) and their magnetic configuration was imaged with X-rays Photoemission Electron Microscopy (X-PEEM). Their findings demonstrate for the first time that is possible, by applying an in-situ electric field, to induce a uniform 90° reorientation of the magnetization in an array of single domain nanoislands from the shape anisotropy induced easy axis to its in-plane orthogonal direction. The observed phenomenon constitutes an important step towards the realization of magnetoelectric magnetic random access memory cells showing giant magnetoelectric coupling, low power consumption and high switching reliability.


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Reference
Single Domain Spin Manipulation by Electric Fields in Strain Coupled Artificial Multiferroic Nanostructures
M. Buzzi, R. V. Chopdekar, J. L. Hockel, A. Bur, T. Wu, N. Pilet, P. Warnicke, G. P. Carman, L. J. Heyderman, and F. Nolting
Physical Review Letter, Volume: 111, Page: 027204 (2013) DOI:10.1103/PhysRevLett.111.027204
Contact
Michele Buzzi, Swiss Light Source
Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
Phone: +41 56 310 3562, e-mail: michele.buzzi@psi.ch


Prof. Dr. Frithjof Nolting, Swiss Light Source
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Phone: +41 56 310 5111, e-mail: frithjof.nolting@psi.ch

5. May 2013

Tiny Magnets as a Model System

Scientists use nano-rods to investigate how matter assembles

In the microscopic world, everything is in motion: atoms and molecules vibrate, proteins fold, even glass is a slow flowing liquid. And during each movement there are interactions between the smallest elements - for example, the atoms - and their neighbours. To make these movements visible, scientists at the Paul Scherrer Institute PSI have developed a special model system. It is so big that it can be easily observed under an X-ray microscope, and mimics the tiniest movements in Nature. The model: rings made from six nanoscale magnetic rods, whose north and south poles attract each other. At room temperature, the magnetisation direction of each of these tiny rods varies spontaneously. Scientists were able to observe the magnetic interactions between these active rods in real time. These research results were published on May 5 in the journal Nature Physics.

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Reference
Exploring hyper-cubic energy landscapes in thermally active finite artificial spin-ice systems
A. Farhan, M. Derlet, A. Kleibert, A. Balan, R. V. Chopdekar, M. Wyss, L. Anghinolfi, F. Nolting & L. J. Heyderman
Nature Physics, Volume: 9, pages: 375-382 (2013), advance online publication 05 May 2013, DOI:10.1038/nphys2613
Contact
Prof. Dr. Laura Jane Heyderman, Laboratory for Micro- und Nanotechnology
Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
Phone: +41 56 310 26 13, e-mail: laura.heyderman@psi.ch

Dr. Peter Derlet, Solid State Theory Group
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Phone: +41 56 310 31 64, e-mail: peter.derlet@psi.ch


3. May 2013

Atomic motions untangled

The pursuit of capturing motion in a movie bears an obvious fascination irrespective of the time scales involved. In the atomic and molecular world where the masses are so light and the distances small the relevant time scale shifts to the subpicosecond range and the motions become frantic especially for larger molecular systems. In the material class of strongly correlated electron materials the intricate balance of competing structural, magnetic and charge interactions complicates the picture when it comes down to disentangle the coupled processes. In order to advance the understanding of the underlying correlations in these materials current efforts focus on the interaction of the atomic, electronic, and magnetic subsystems on their relevant time scales. In particular, femtosecond x-ray or electron diffraction received considerable attention in the recent past because they enable direct access to the evolving atomic and electronic structure. Here, we study specific lattice modulations coupled to the melting of charge and orbital order in a manganite by means of femtosecond x-ray diffraction. By using a carefully chosen set of reflections combined with structure factor calculations we are able to identify the involved atomic motions.

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Original publication
Identification of coherent lattice modulations coupled to charge and orbital order in a manganite
A. Caviezel, S. O. Mariager, S. L. Johnson, E. Möhr-Vorobeva, S. W. Huang, G. Ingold, U. Staub, C. J. Milne, S.-W. Cheong and P. Beaud
PHYSICAL REVIEW B 87, 205104 (2013), DOI: 10.1103/PhysRevB.87.205104
Contact
Andrin Caviezel, Swiss Light Source
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Phone: +41 56 310 5185, e-mail: andrin.caviezel@psi.ch


Dr. Paul Beaud, Swiss Light Source
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Phone: +41 56 310 4121, e-mail: paul.beaud@psi.ch



25. March 2013

Soft x-ray photoelectron spectroscopy on buried complex oxide interfaces: a new method to diagnose authentic protected electronic structures

Exotic phenomena at interfaces of complex oxides are highly promising for future solid-state electronics applications. A prominent example is the interface of two wide band gap insulators formed by growing a LaAlO3 layer on TiO2-terminated SrTiO3 substrate. When the LaAlO3 thickness exceeds 3 unit cells this system undergoes a sharp insulator-to-metal transition with a two-dimensional electron gas (2DEG) appearing at the interface. A team of scientists from the Paul Scherrer Institute and University of Geneva, Switzerland, has investigated the LaAlO3/SrTiO3 interface with photoelectron spectroscopy. The researchers have for the first time unambiguously directly detected the 2DEG signal at the Fermi level with its sharp onset between the insulating and conducting interfaces. Furthermore, they determined the spatial localization depth of the conducting sheet. The problem of absorption and inelastic scattering of the photoelectrons as they pass through the LaAlO3 overlayer was solved by using advanced synchrotron-based instrumentation delivering a high photon flux, and operating in the soft-X-ray energy range where the photoelectron escape depth increases. Furthermore, in consequence of the very small number of electrons in the 2DEG, their photoelectron signal was boosted by tuning the photon energy to resonant excitation of the core electrons, through a Fanolike process. This work represents a significant methodological advance in resonant photoemission spectroscopy of buried interfaces.

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Original publication
Interface Fermi States of LaAlO3/SrTiO3 and Related Heterostructures
C. Cancellieri, M. L. Reinle-Schmitt, M. Kobayashi, V. N. Strocov, T. Schmitt, P. R. Willmott, S. Gariglio and J.-M. Triscone
Phys. Rev. Lett. 110, 137601 (2013), DOI: 10.1103/PhysRevLett.110.137601
Contact
Dr. Claudia Cancellieri; Swiss Light Source
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Phone: +41 56 310 5689, e-mail: claudia.cancellieri@psi.ch


6. February 2013

Imaging fluctuations with X-ray microscopy

X-rays allow an inside look at structures that cannot be imaged using visible light. They are used to investigate nanoscale structures of objects as varied as single cells or magnetic storage media. Yet, high-resolution images impose extreme constraints on both the X ray microscope and the samples under investigation. Researchers at the Technische Universität München, Germany, and the Paul Scherrer Institut in Villigen, Switzerland, now showed how to relax these conditions without loss of image quality. They further showed how to image objects featuring fast fluctuations, such as the rapid switching events that determine the life time of data storage in magnetic materials. They demonstrated their method with an experiment at the Swiss synchrotron SLS and with computer simulations. The results have been published in the science journal Nature.

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Original publication
Reconstructing state mixtures from diffraction measurements
Pierre Thibault, Andreas Menzel, Nature, 7. February 2013
DOI: 10.1038/nature11806
Contact
Dr. Andreas Menzel; Labor für Makromoleküle und Bioimaging
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Phone: +41 56 310 3711, e-mail: andreas.menzel@psi.ch [German, English]

Dr. Pierre Thibault; Physikdepartment
Technische Universität München, 85748 Garching, Germany
Phone: +49 (0)89 289 14397, e-mail: pierre.thibault@tum.de [French, English]

22. January 2013

Magnetic nano-chessboard puts itself together

Researchers switch the quantum properties of magnetic molecules

Researchers from the Paul Scherrer Institute and the Indian Institute of Science Education and Research (Pune, India) have managed to ‘turn off’ the magnetization of every second molecule in an array of magnetized molecules and thereby create a ‘magnetic chessboard’. The magnetic molecules were so constructed that they were able to find their places in the nano-chessboard by themselves. Thus the nano-chessboard effectively built itself together. The researchers were able to manipulate the quantum state of just a part of the molecules in a specific way. Being able to specifically alter the state of individual quantum objects is an important prerequisite for the development of quantum computers. Such computers would rely on the laws of quantum physics and could perform some calculational tasks very much faster than present-day computers. However, today we are very far from being able to build quantum computers that are in reality comparably powerful for particular calculations. The scientists have published their results in the journal Advanced Materials.

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Reference
Two-dimensional Supramolecular Electron Spin Arrays
C. Wäckerlin, J. Nowakowski, S.-X. Liu, M. Jaggi, D. Siewert, J. Girovsky, A. Shchyrba, T. Hählen, A. Kleibert, P. M. Oppeneer, F. Nolting, S. Decurtins, T. A. Jung, N. Ballav
Advanced Materials 2013, Advance online publication 22. Januar 2013, DOI: 10.1002/adma.201204274
Contact
Christian Wäckerlin, Laboratory for Micro- und Nanotechnology
Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
Tel. +41 56 310 52 44, christian.waeckerlin@psi.ch

Prof. Dr. Thomas Jung, Laboratory for Micro- und Nanotechnology
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Tel. +41 56 310 45 18, E-Mail: thomas.jung@psi.ch

Prof. Dr. Nirmalya Ballav, Department of Chemistry,
Indian Institute of Science Education and Research, 411 008 Pune, India
Tel: +91 20 2590 8215, E-mail: nballav@iiserpune.ac.in