Missions

Today's information society is increasingly dependent on the availability of faster communication in ever-smaller devices. To sustain technological progress, new fundamental ideas are needed. Towards that direction, the discovery of an optically induced ultrafast magnetization, more than a quarter of a century ago, has triggered a tremendous interest [1]. However, the optically induced transfer of angular momentum between different reservoirs, in a magnetic system, is still an open question puzzling researchers in the quest for a microscopic description of ultrafast spin dynamics [2]. In this context, ferromagnet-heavy metal (FM-HM) based thin films have been extensively used to study ultrafast magnetization dynamics due to the ease of tailoring their magnetic properties. These studies yielded a suite of interesting results, which gave rise to the development of several theories [3-6]. However, it is not clear if those different experimental results are due to intrinsic properties (e.g. magnetic anisotropy, sample stoichiometry), sample morphology (e.g. interface quality, crystallinity) or the different means of probing. Therefore a general understanding of the ultrafast magnetization dynamics in these important systems for spintronic applications has so far not emerged. In order to converge on a consensus about the microscopic mechanisms controlling ultra-fast dynamics, the overall goal of this position is to conduct a systematic study of magnetic systems composed of 3d transition metals (e.g. Co or Fe) and 4d/5d heavy metals (e.g. Pt or Pd) to understand the different magnetization dynamics observed in these systems. The goal of this postdoc position is to advance our understanding of ultrafast magnetization dynamics on three points: (i) determine the contribution and the importance of the different intrinsic microscopic mechanisms, (ii) distinguish how different experimental techniques can bring different types of information and (iii) assess the importance of the exact structure of the sample.

[1] Beaurepaire, et al, Ultrafast Spin Dynamics in Ferromagnetic Nickel. PRL 76, 4250, 1996
[2] Scheid, et al, Light-induced ultrafast magnetization dynamics in metallic compounds. JMMM 560, 169596 2022
[3]* Hennes, et al, Element-Selective Analysis of Ultrafast Demagnetization in Co/Pt Multilayers Exhibiting Large Perpendicular Magnetic Anisotropy. APL 120, 072408, 2022
[4] Willems, et al, Probing Ultrafast Spin Dynamics with High-Harmonic Magnetic Circular Dichroism Spectroscopy. PRB 92, 220405, 2015
[5] Yamamoto, et al, Element-Selectively Tracking Ultrafast Demagnetization Process in Co/Pt Multilayer Thin Films by the Resonant Magneto-Optical Kerr Effect. APL 116, 172406, 2020
[6] Vaskivskyi, et al, A. Element-Specific Magnetization Dynamics in Co–Pt Alloys Induced by Strong Optical Excitation. J. Phys. Chem. C 125, 11714, 2021

Activities

- samples growth by magnetron sputtering
- static and time-resolved magneto-optical Kerr effect experiment
- Experiment on synchrotron and free-electron laser or high-order harmonic generation sources
- analysis of data from large-scale facilities (synchrotron, free electron laser)
- physical interpretation of the results obtained in relation to the bibliography
- writing of articles and presentations at national and international conferences

Skills

- strong expertise in magnetism and/or time-resolved condensed matter experiments
- demonstrated track record of performing good research with autonomy and enthusiasm
- strong written and verbal communication skills.

Work Context

Our research group (Strongly Correlated and Magnetic Materials) is part of the Laboratory of Physical Chemistry - Matter and Radiation (LCPMR), a joint research unit of the Sorbonne Université and the CNRS, which is located on the Pierre et Marie Curie campus in downtown Paris (5th arrondissement). The research groups of the LCPMR are known for their expertise in the application of advanced XUV/X-ray spectroscopies and scattering techniques for the investigation of electronic properties of matter, from atoms and molecules to condensed matter, and their dynamics.
For the past 15 years, our team at LCPMR has been at the forefront of the research on ultrafast magnetization dynamics using extreme ultraviolet (XUV) and X-ray femtosecond sources bringing nanometer scale and element selectivity to the field. This was done by developing advanced spectroscopic experiments at different state-of-the-art HHG and XFEL sources and brought numerous breakthrough results such as indirect ultrafast demagnetization [7], transient inhomogeneous magnetic depth profile [8,9] ultrafast dynamics of magnetic anisotropy [10] and interplay of charge and spin dynamics [11]. To realize our time-resolved experiments we have developed strong collaborations with the LOA (Laboratoire d'Optique Appliquée, Palaiseau, France) for all optical and HHG (High Harmonic Generation) experiments; the free electron lasers FLASH (Hambourg, Germany), FERMI (Trieste, Italy) and European XFEL (Schenefeld, Germany) for XUV/X-ray experiments. The postdoc will benefit from these established collaborations for the realization of his/her research project. He/she will be part of a team consisting of a CNRS research scientist, 1 assistant professor, 1 professor, 1 research engineer, 1 engineer and 3 PhD students.


[7]* Vodungbo, et al, Indirect Excitation of Ultrafast Demagnetization. Sci. Rep. 6, 18970, 2016
[8]* Jal, et al, Structural dynamics during laser-induced ultrafast demagnetization. PRB 95, 184422, 2017
[9]* Chardonnet, et al, Toward ultrafast magnetic depth profiling using time-resolved x-ray resonant magnetic reflectivity. Struct. Dyn. 8, 0340305, 2021
[10]* Hennes, et al, Laser-induced ultrafast demagnetization and perpendicular magnetic anisotropy reduction in a Co88Tb12 thin film with stripe domains. PRB 102, 174437, 2020
[11]* Hennes, et al, Time-Resolved XUV Absorption Spectroscopy and Magnetic Circular Dichroism at the Ni M2,3-Edges. Applied Science, 11, 325, 2021