Dr. Armin Kleibert

Armin Kleibert is staff scientist in the Microscopy and Magnetism Group in the Laboratory Condensed Matter of the Photon Science Division of PSI. He studied physics at the University of Rostock (Germany) and received his Ph. D. in the Lab of Karl-Heinz Meiwes-Broer in 2006 in the field of nanoparticle magnetism and x-ray magneto-optics. He joined PSI in 2008 as a Postdoc in the Microscopy and Magnetism Group, where he pioneered the use of x-ray photoemission electron microscopy for the investigation of magnetic, electronic and chemical properties in individual nanoparticles. In 2010 he assumed the position of a beamline scientist at the Surface/Interface:Microscopy beamline of the Swiss Light Source. Since 2013 he is tenured staff scientist at PSI. He is reviewer for various funding agencies including  Deutsche Forschungsgemeinschaft and the European Science Foundation and serves as a referee for a range of scientific journals including Nature Communications and Physical Review Letters.

Armin Kleibert is responsible for the operation of the Surface/Interface: Microscopy beamline of the Swiss Light Source. At this beamline we operate, develop, and provide user support for soft x-ray photoemission electron microscopy and soft x-ray absorption spectroscopy for fundamental and applied science studies in areas ranging from catalysis to nanomagnetism. We contribute to the development of critical infrastructure for the Photon Science Division of PSI, including x-ray and electron detectors, advanced x-ray optics, and new synchrotron x-ray measurement techniques (such as near ambient pressure photoemission, micros XPS, laminography, soft x-ray ptychography) for the characterization of condensed matter at the nanometer scale.

Armin Kleibert’s research is focused on the magnetic, electronic and chemical properties of nanoparticles. He has discovered metastable magnetism, non-collinear spin structures and energetically excited states with enhanced magnetic anistropies in 3d transition metal nanoparticles. Present research projects combine a unique set of microscopy techniques such as x-ray photoemission electron microscopy, scanning electron microscopy, and high resolution transmission electron microscopy to correlate magnetism with chemical composition, electronic structure, microstructure, and size of nanoparticles of ferromagnetic, ferrimagnetic, antiferromagnetic and multiferroic materials and their manipulation using stimuli such as femtosecond laser pulses or in chemical reactions. He is further pushing the development of soft x-ray ptychography to overcome current limitations in soft x-ray microscopy for the investigation of the internal spin structure of nanomagnets.

For an extensive overview we kindly refer you to our publication repository DORA and the profiles on ResearcherID, ORCID, or Google Scholar.

Single femtosecond laser pulse excitation of individual cobalt nanoparticles, T. M. Savchenko, M. Buzzi, L. Howald, S. Ruta, J. Vijayakumar, M. Timm, D. Bracher, S. Saha, P. M. Derlet, A. Béché, J. Verbeeck, R. W. Chantrell, C. A. F. Vaz, F. Nolting, and A. Kleibert, Phys. Rev. B 102, 205418  (2020)
The interaction of light and magnetism at the nanoscale is a topic of fundamental interest and with potential impact to future spintronics applications. This work addresses theoretically and experimentally the effect of femtosecond laser pulse excitation on the magnetic, structural, and chemical stability of individual magnetic cobalt nanoparticles including the role of the substrate or matrix. Based on these results, possible pathways to achieve laser-induced magnetic switching in individual nanostructures are discussed.

Chirally Coupled Nanomagnets, Z. Luo, T. Phuong Dao, A. Hrabec, J. Vijayakumar, A. Kleibert, M. Baumgartner, E. Kirk, J. Cui, T. Savchenko, G. Krishnaswamy, L. J. Heyderman, and P. Gambardella, Science 363, 1435 (2019)
Magnetically coupled nanomagnets have multiple applications in nonvolatile memories, logic gates, and sensors. In this work x-ray photoemission electron microscopy is used to reveal the chirality in the coupling of out-of-plane and in-plane magnetized regions of nano-sized Pt/Co/AlO_x trilayers. The findings provide a platform to design arrays of correlated nanomagnets and to achieve all-electric control of planar logic gates and memory devices.

Enhanced Mobility of Iron Nanoparticles Deposited onto a Xenon-Buffered Substrate, C. A. F. Vaz, C. Piamonteze, and A. Kleibert, J. Magn. Magn. Mat. 459, 2 (2018)
The growth of nanoparticles from the gas phase in combination with deposition under ultrahigh vacuum conditions enables one to obtain pure and mass-selected nanoparticles with variable particle density from a wide range of materials on virtually any solid support and is therefore of great interest for many applications. In this work we demonstrate that deposition of nanoparticles onto a Xenon-buffer layer enables one to control the lateral mobility of nanoparticles upon deposition, which can be combined in future with structured substrates to achieve a control over the spatial arrangement of nanoparticles on surfaces.

Direct Observation of Enhanced Magnetism in Individual Size- and Shape-Selected 3d Transition Metal Nanoparticles, A. Kleibert, A. Balan, R. Yanes, P. M. Derlet, C. A. F. Vaz, M. Timm, A. Fraile Rodríguez, A. Béché, J. Verbeeck, R. S. Dhaka, M. Radovic, U. Nowak, and F. Nolting, Phys. Rev. B 95, 195404 (2017)
Magnetic nanoparticles are critical building blocks for future technologies ranging from nanomedicine to spintronics. However, despite significant experimental efforts the magnetism of nanoparticles is poorly understood, even in the canonical ferromagnetic 3d transition metals. In this work we assign the enhanced magnetism in Fe and Co nanoparticles to metastable structural modifications in the core of the nanoparticles and demonstrate the importance of complementary single particle investigations for a better understanding of nanoparticle magnetism and for full exploration of their potential for applications.

Emergent Dynamic Chirality in a Thermally Driven Artificial Spin Ratchet, S. Gliga, G. Hrkac, C. Donnelly, J. Büchi, A. Kleibert, J. Cui, A. Farhan, E. Kirk, R. Chopdekar, Y. Masaki, N. S. Bingham, A. Scholl, R. L. Stamps, and L. J. Heyderman, Nat. Mater. 16, 1106 (2017)
Modern nanofabrication techniques have opened the possibility to create novel functional materials, whose properties transcend those of their constituent elements. Here, we demonstrate a spin-ice-based active material in which energy is converted into unidirectional dynamics. Using x-ray photoemission electron microscopy we show that the collective rotation of the average magnetization proceeds in a unique sense during thermal relaxation.  These findings opens the possibility of implementing a magnetic Brownian ratchet, which may find applications in novel nanoscale devices, such as magnetic nanomotors, actuators, sensors or memory cells.

Catalyst Support Effects on Hydrogen Spillover, W. Karim, C. Spreafico, A. Kleibert, J. Gobrecht, J. VandeVondele, Y. Ekinci, and J. A. van Bokhoven, Nature (London) 541, 68 (2017)
In spillover reactions hydrogen molecules are split at one site of a sample and the released hydrogen atoms react with molecules or atoms at another. In this work we combine x-ray photoemission electron microscopy with nanolithography to investigate the reduction of individual iron oxide nanoparticles at variable distances to platinum nanoparticles on titanium oxide and aluminium oxide supports. We find fast hydrogen spillover on titanium oxide reducing remote iron oxide nanoparticles via coupled proton–electron transfer. In contrast, spillover on aluminium oxide is mediated by three-coordinated aluminium centres that also interact with water and that give rise to hydrogen mobility competing with hydrogen desorption.

Nanoscale XPEEM Spectromicroscopy (Book Chapter) C. A. F. Vaz, A. Kleibert, and M. El Kazzi, 21st Century Nanoscience – A Handbook: Advanced Analytical Methods and Intrumentation (Volume 3), Edited by Klaus D. Sattler (CRC Press, Taylor&Francis Group, Boca Raton – London – New York, 2020)