While the origin of magnetic order in condensed matter is in the exchange and spin-orbit interactions, with characteristic time scales in the femto- and subpicosecond ranges, it has been long believed that magnetism could only be manipulated at nanosecond rates, exploiting dipolar interactions with external magnetic fields. However, in the past decade researchers have been able to observe ultrafast magnetic dynamics at its intrinsic time scales without the need for magnetic fields, thus revolutionising the view on the speed limits of magnetism.
Despite many achievements in ultrafast magnetism, the understanding of the fundamental physics that allows for the ultrafast dissipation of angular momentum is still only partial, hampered by the lack of experimental techniques suited to fully explore these phenomena. However, the recent appearance of two new types of coherent radiation, single-cycle THz pulses and x-rays generated at free electron lasers (FELs), has provided researchers access to a whole new set of capabilities to tackle this challenge. These novel techniques have already produced breakthroughs, but we are only at the beginning of a new era of scientific investigations that uses them.
Within the MAGNETIC-SPEED-LIMIT project, we we these novel techniques to achieve an encompassing view of ultrafast magnetic dynamics in metallic ferromagnets, via the following three research objectives:
- to reveal ultrafast dynamics driven by strong THz radiation in several magnetic systems using table-top femtosecond laser;
- to unravel the contribution of lattice dynamics to ultrafast demagnetization in different magnetic materials using the x-rays produced at existing and soon-operating FELs;
- to directly image ultrafast spin currents by creating femtosecond movies with nanometre resolution.
Research Highlights (project still running):
Inertial spin dynamics in ferromagnets, Nature Physics (2020): we report on the first experimental observation of nutation in magnetic thin films. The results have been highlighted in several dissemination channels:
- Twitter: research group account, and dedicated tweet by the Editor of Nature Physics
- Ca' Foscari Webpage
- Webpage of the Department of Physics at Stockholm University
- EurekAlert! by the American Association for the Advancement of Science
Nonlinear magnetization dynamics driven by strong terahertz fields, Physical Review Letters (2019): we show that intense terahertz fields can drive nonlinear magnetization dynamics in ferromagnetic thin films. Results disseminated via:
- Twitter: research group channel
- D. Ksenzov, A. Maznev, V. Unni, F. Bencivenga, F. Capotondi, A. Caretta, L. Foglia, M. Malvestuto, C. Masciovecchio, R. Mincigrucci, K. Nelson, M. Pancaldi, E. Pedersoli, L. Randolph, H. Rahmann, S. Urazhdin, S. Bonetti, C. Gutt, Nanoscale transient magnetization gratings excited and probed by femtosecond extreme ultraviolet pulses, submitted to Science Advances (2020), arXiv:2009.13330
- V. Unikandanunni, R. Medapalli, E. E. Fullerton, K. Carva, P. M. Oppeneer, S. Bonetti, Anisotropic Ultrafast Spin Dynamics in Epitaxial Cobalt, under review in Physical Review Letters (2020), arXiv:2008.03119
- K. Neeraj, N. Awari, S. Kovalev, D. Polley, N. Zhou Hagström, S.S.P.K. Arekapudi, A. Semisalova, K. Lenz, B. Green, J.-C. Deinert, I. Ilyakov, M. Chen, M. Bawatna, V. Scalera, M. d'Aquino, C. Serpico, O. Hellwig, J.-E. Wegrowe, M. Gensch, S. Bonetti, Inertial spin dynamics in ferromagnets, Nature Physics (2020) arXiv:1910.11284
- L. Alber, V. Scalera, V. Unni, D. Schick, S. Bonetti, NTMpy: An open source package for solving coupled parabolic differential equations in the framework of the three-temperature model, under review in Computer Physics Communications (2020), arXiv:2002.04559
- V. Scalera, M. Hudl, K. Neeraj, S. Perna, M. d’Aquino, S. Bonetti, C. Serpico Analysis in k-space of Magnetization Dynamics Driven by Strong Terahertz Fields, IEEE Transactions on Magnetics (2020), arXiv:2005.05742
- M. Hudl Waltin, M. d’Aquino, M. Pancaldi, S.-H. Yang, M.G. Samant, S.S.P. Parkin, C. Serpico, H.A. Dürr, M.C. Hoffmann, S. Bonetti, Nonlinear magnetization dynamics driven by strong terahertz fields, Physical Review Letters 123, 197204 (2019), arXiv:1903.08395
- P. Salén, M. Basini, S. Bonetti, J. Hebling, M. Krasilnikov, A. Nikitin, G. Shamuilova, Z. Tibaic, V. Zhaunerchyk, V. Goryashko, Matter Manipulation with Extreme Terahertz Light: progress in the enabling THz technology, Physics Reports 836-837, 1 (2019)
- D. Polley, N. Zhou Hagström, C. von Korff Schmising, S. Eisebitt, S. Bonetti, Terahertz magnetic field enhancement in an asymmetric spiral metamaterial, Journal of Physics B: Atomic Molecular and Optical Physics 51, 224001 (2018), arXiv:1806.10100.
Part of the invited papers on the joint Special Issue on ultrafast spectroscopy: fundamentals Guest Editors Keith Nelson (MIT, USA), A. Leitenstorfer (U. of Konstanz, Germany), K. Tanaka (U. of Kyoto, Japan)
- D. Polley, M. Pancaldi, M. Hudl, P. Vavassori, S. Urazhdin, S. Bonetti, THz-driven demagnetization with Perpendicular Magnetic Anisotropy: Towards ultrafast ballistic switching, Journal of Physics D: Applied Physics 51, 084001 (2018), arXiv:1711.01234
- M. Pancaldi, R. Freeman, M. Hudl, M. Hoffmann, S. Urazhdin, P. Vavassori, S. Bonetti, Anti-reflection coating design for metallic THz meta-materials, Optics Express 26, 2917 (2018), arXiv:1711.05670
Peer-Reviewed International Conferences
- N. Zhou Hagström et al., Ultrafast Holographic Imaging at the European XFEL, MMM 2019, International Conference on Magnetism and Magnetic Materials, Las Vegas, NV, USA November 4 - 8, 2019
- K. Neeraj et al., Direct experimental evidence of inertial dynamics in ferromagnetic thin films, MMM 2019, International Conference on Magnetism and Magnetic Materials, Las Vegas, NV, USA November 4 - 8, 2019
- D. Polley et al., Terahertz induced Demagnetization in Magnetic Multilayers, MMM 2019, International Conference on Magnetism and Magnetic Materials, Las Vegas, NV, USA November 4 - 8, 2019
- V. Unni et al., Anisotropic spin relaxation in epitaxial cobalt films following ultrafast demagnetization, MMM 2019, International Conference on Magnetism and Magnetic Materials, Las Vegas, NV, USA November 4 - 8, 2019
- K. Neeraj et al., Direct experimental evidence of inertial dynamics in ferromagnetic thin films, Ultrafast Magnetism Conference 2019, York, UK, October 14-17, 2019
- D. Polley et al., Terahertz induced Demagnetization in Magnetic Multilayers, Ultrafast Magnetism Conference 2019, York, UK, October 14-17, 2019
- Björn Wehinger et al., Spin and Lattice Correlations in SrCu2(BO3)2 Probed by High-Pressure Ultrasound Under High Magnetic Fields, New Generation in Strongly Correlated Electrons Systems, Pescara, Italy, September 2-6, 2019
- K. Neeraj et al., Direct experimental evidence of inertial dynamics in ferromagnetic thin films, JEMS 2019, Joint European Magnetic Symposia, Uppsala, Sweden, August 26 - 30, 2019
- S. Bonetti et al., Ultrafast spin dynamics in anisotropic metallic systems, Gordon Research Conference: Ultrafast Phenomena in Cooperative Systems Lucca, Italy, February 2 - 7, 2020
- Björn Wehinger, Hybridized spin-lattice correlations in quantum magnets, 5th Workshop on ab initio phonon calculations, Cracow, Poland, December 3–6, 2019
- N. Zhou Hagström et al., Ultrafast Holographic Imaging at the European XFEL, 31st Max IV user meeting, Lund, September 23 – 25, 2019
- M. Pancaldi et al., Spiral metamaterials for terahertz magnetic field enhancement, META 2019, the 10th International Conference on Metamaterials, Photonic Crystals and Plasmonics, Lisbon, Portugal, July 23 - 26, 2019
- S. Bonetti et al., Magnetic-field enhancing terahertz metamaterials, META 2019, the 10th International Conference on Metamaterials, Photonic Crystals and Plasmonics, Lisbon, Portugal, July 23 - 26, 2019
- S. Bonetti et al., Terahertz spin dynamics, MORIS 2019, Magnetics and Optics Research International Symposium, Prague, Czech Republic, June 23 - 26, 2019
- S. Bonetti et al., Terahertz spin dynamics, MML 2019, International Symposium on Metallic Multilayers, Madrid, Spain, June 17 - 21, 2019
- S. Bonetti et al., THz probing and manipulation of magnetism, SPIE Optics + Photonics, Spintronics XI, San Diego, CA, USA, August 22, 2018
- S. Bonetti et al., THz control of magnetism with metamaterials, SPIE Optics + Photonics, Terahertz Emitters, Receivers, and Applications IX, San Diego, CA, USA, August 19, 2018
- S. Bonetti et al., THz spin dynamics, 2nd IEEE Conference on Advances in Magnetics, La Thuille, Italy, February 4 - 7, 2018
- S. Bonetti et al., THz-driven ultrafast magnetization dynamics, Ultrafast Magnetism Conference 2017, Kaiserslautern, Germany, October 9 - 13, 2017
- S. Bonetti et al., THz-driven Ultrafast Spin-Lattice Scattering in Metallic Ferromagnets, FISMAT 2017 - Italian National Conference on Condensed Matter Physics, Trieste, Italy, October 1 - 5, 2017
- S. Bonetti et al., Probing and controlling magnetism with light, Magnet 2017 Assisi (Italy), September 13 - 15, 2017, Keynote speaker
- S. Bonetti et al., THz-driven spin dynamics: a new light on old questions, Gordon Research Conference: Spin Dynamics in Nanostructures Les Diablerets, Switzerland, July 16 - 21, 2017
Invited at workshops, seminars, colloquia, lectures (by S. Bonetti)
- Workshop: Ultrafast coherent soft x-ray imaging: making movies at the nanoscale , FUSEE - Future of Seeded Free Electron Lasers, Trieste, Italy, December 10-11, 2019
- Lecture: Ultrafast Dynamics through X-ray pump-probe experiments, ELISS - ELI Summer School, Prague, Czech Republic, August 26 - 30, 2019
- Seminar: Terahertz spin dynamics, FERMI Science Colloquium, FERMI-Elettra, Trieste, February 14, 2019
- Workshop: Terahertz-driven spin dynamics: towards ultrafast coherent magnetization switching, Center for Quantum Spintronics (QuSpin) International Workshop, Trondheim, Norway, October 4 - 5, 2018
- Workshop: THz-driven spin dynamics, 2nd International Workshop on Magnetic Materials and Nanomaterials, Boumerdes, Algeria, July 1 - 4, 2018
- Workshop: X-ray imaging of spin currents and magnetisation dynamics at the nanoscale, The 9th International Workshop on Nanoscale Spectroscopy and Nanotechnology, Gyeongju, South Korea, September 25 - 28, 2017.
- Seminar: THz-driven Ultrafast Spin-Lattice Scattering In Metallic Ferromagnets, THz workshop at XFEL, Hamburg, Germany June 1--2, 2017
- Open Lecture: From attracting stones to the memory of the internet: the wonders of magnetism, Fysikum, Stockholm University April 27, 2017
- Pulse energy output: >7 mJ
- Pulse duration: 35-40 fs
- Repetition rate: 1 kHz
Optical parametric amplifier
- Pulse energy output: 3 mJ (signal + idler)
- Pulse duration: 50-80 fs
- Repetition rate: 1 kHz
- Average power: 550 mW
- Pulse duration: 25 fs (can be compressed <10 fs)
- Repetition rate: 80 MHz
Debanjan's research interests are in THz spectroscopy of nanostructures, THz metamaterials, magnetization dynamics and spintronics. He has worked at S. N. Bose National Centre for Basic Sciences, Kolkata, India under the guidance of Dr. Rajib Kumar Mitra and Prof. Anjan Barman. He defended his Ph.D. thesis “Manipulating Terahertz Radiation Using Nanostructures” on July, 2016. He will join our group at Stockholm University March 2017 as a post-doctoral fellow, where he will investigate spin transport and dynamics in terahertz regime. Besides his work, Debanjan enjoys reading historical fictions, playing table tennis, trekking and exploring new places.
Matteo obtained his Ph.D. from the Nanomagnetism group in the nanoGUNE Consolider Research Center (San Sebastian, Spain), under the supervision of Dr. Paolo Vavassori. He received the Master degree in Physics from the University of Bologna, Italy, in December 2013. His research topics include the study of artificially frustrated magnetic systems and the magneto-optical characterization of magnetic nanostructures. His research will focus on the nonlinear spin dynamics driven by strong terahertz radiation.
Neeraj obtained his B.Sc (Hons.) in Physics from Kirorimal College, University of Delhi, India. He obtained his M.Sc in Physics from SN Bose National Centre for Basic Sciences, Kolkata, India. He completed his master thesis under the supervision of Dr. Rajib Kumar Mitra and Prof. Anjan Barman, studying the ground state opto-electronic properties of carbon nanotube films and their use as effective electromagnetic interference shielding device in the THz region. He was also involved in micro fabrication of polarizers and antidot structures for THz studies. Apart from research, he takes keen interest in football, reading, listening good music. He is pursuing his Ph.D. in Spin transport and Dynamics in the Terahertz Regime.
Vivek obtained his M.Sc. (Physics) with specialization in photonics and B.Sc. (Hons.) in physics, from Sri Sathya Sai Institute of Higher Learning, India. He completed his master’s thesis in the topic “No cloning Theorem” under the supervision of Prof. Debendranath Sahoo. He has been working as Junior Research Fellow in the Multimodal Microscopy project funded by Department of Science and Technology, Government of India from July 2016. His other interests include Science education, World Cinema, Cricket, Football and International affairs. He is pursuing his Ph.D. in Ultrafast Spins: The Role of Lattice and Electrons.
Nanna Zhou Hagström
Nanna obtained both her B.Sc and M.Sc in Physics from Université Pierre et Marie Curie in Paris, and has a B.Sc in Mathematics from Stockholm University. During her master she did two internships at the Stanford Synchrotron Radiation Lightsource (SSRL) in California. During Spring 2016 she studied mackinawite, an iron sulfide that adapts to oxidative impurities, through X-ray absorption spectroscopy at SSRL, under the supervision of John Bargar and Vincent Noël. In 2017 she spent 5 months under the supervision of Michael Toney (SSRL) and Ana Flavia Nogueira (University of Campinas, Brazil) studying hybrid organic-inorganic mixed halide perovskite, a solar absorber, through synchrotron X-ray diffraction. She is pursuing her Ph.D. in ultrafast imaging of spin dynamics at the nanoscale.