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Team
- Permanent members: Maurizio Sacchi, Stéphane Chenot, Mahmoud Eddrief, Franck Vidal, Marcel Hennes, Yunlin Zheng
- PhD students: Carlos Cortéz, Moundji Hemili (iMAT scholarship, co-supervision LCPMR)
Our research deals with magnetization control in thin films and nanostructures using ultrashort optical pulses. We study systems exhibiting magneto-structural phase transitions (FeRh, MnAs), matrix-embedded nanowires, ferrimagnetic rare earth – transition metal thin films and ferromagnetic multilayers with out-of-plane anisotropy (Co/Pt). Our experiments rely on the use of X-FELs (X-ray free electron lasers) as well as on measurement techniques employing table-top laboratory laser sources (tr-MOKE, XRMS).
Research topics
- Non inductive reversal of the magnetization. Preparation and characterization of hybrid magnetic systems based on MnAs and FeRh. The reversal of the magnetization of an additional layer (Fe or Co) can be obtained by controlling the surface dipole field, either thermally, or by the absorption of a single laser fs pulse. The dynamics are studied by diffusion and X-ray diffraction using synchrotron, HHG and FEL sources.
Figure 1: Left: Schematic representation of the temperature-assisted magnetization reversal process in Fe / MnAs / GaAs (001). Right: Reversal triggered by a single laser pulse.
- MnAs: structural dynamics studied by time-resolved diffraction (pump: laser, X-ray probe). Correlation between the evolution of the structure and the magnetism for non inductive reversal. Study of phonons and ultrafast phase transitions.
Figure 2: (a) Measurements carried out at the LCLS FEL, with a temporal resolution of 50 fs. The oscillations of the diffracted intensity observed, for several reflections, up to 2 ps after the laser excitation and the corresponding calculations (b) show a soft phonon mode of THz frequency. The atomic movements in the orthorhombic lattice of β-MnAs take place along the path which reduces the distortion (c) and leads to the hexagonal structure (α and γ phases). These oscillations precede a sequence of phase transitions which extends over several tens of ps (d). The pump-probe measurements carried out at CRISTAL (SOLEIL) with a temporal resolution of ~ 80 ps (e) finally allow the structural dynamics to be followed over 1 μs during the return to equilibrium, after the laser excitation.
- Optically induced magnetization dynamics in nanostructures : we study the impact of femtosecond laser pulses on the magnetization and anisotropy of ferro- and ferrimagnetic thin films and nanostructures. Magnetic (pump-probe) scattering experiments (tr-XRMS) allow to analyse the temporal evolution of the magnetic texture with elemental sensitivity and nanometer spatial resolution.
Figure 3 : a) Co/Pt multilayers. Perpendicular magnetic anisotropy gives rise to nanometer-sized magnetic domains. HHG-based pump-probe experiments allow to study magnetization dynamics with elemental sensivity (blue : Co, orange : Pt) and yield evidence for a delay of the response of the Pt sub-system of approximately 10-20 fs. b) Ferromagnetic nanowires embedded in SrTiO3 matrix. Optically induced magnetization quenching as a function of the IR excitation fluence (tr-MOKE) : the quenching amplitude depends on the polarisation of the pump pulse.
Collaborations
- LCPMR
- LOA
- Synchrotron SOLEIL
- Sincrotrone Trieste
Recent publications
- M. Hennes, G. Lambert, V. Chardonnet, R. Delaunay, G. S. Chiuzbăian, E. Jal, B. Vodungbo, Element-selective analysis of ultrafast demagnetization in Co/Pt multilayers exhibiting large perpendicular magnetic anisotropy (In Special Collection: Ultrafast and Terahertz Spintronics, invited), Appl. Phys. Lett. 120, 072408 (2022) https://hal.science/hal-03639146/document
- F. Vidal, Y. Zheng, L. Lounis, L. Coelho, C. Laulhé, C. Spezzani, A. Ciavardini, H. Popescu, E. Ferrari, E. Allaria, J. Ma, H. Wang, J. Zhao, M. Chollet, M. Seaberg, R. Alonso-Mori, J. M. Glownia, M. Eddrief, and M. Sacchi, Ultrafast Structural Dynamics along the β−γ Phase Transition Path in MnAs, Phys. Rev. Lett. 122, 145702 (2019). https://hal.archives-ouvertes.fr/hal-02096578
- L. Lounis , Y. Zheng , C. Spezzani , E. Ferrari , M. Edrrief , A. Ciavardini , H. Popescu, E. Allaria , C. Laulhé , F. Vidal , M. Sacchi, Dynamics of laser induced magneto-structural phase transitions in MnAs/GaAs(001) epitaxial layers IEEE Trans. Mag. 53, 8205004 (2017) https://hal.archives-ouvertes.fr/hal-02106193
- L. Lounis, C. Spezzani, R. Delaunay, F. Fortuna, M. Obstbaum, S. Günther, C. H. Back, H. Popescu, F. Vidal and M. Sacchi, Temperature and field dependent magnetization in a sub-μm patterned Co/FeRh film studied by resonant x-ray scattering. J. Phys. D : Appl. Phys. 49, 205003 (2016) https://hal.sorbonne-universite.fr/hal-01323817
- C. Spezzani, F. Vidal, R. Delaunay, M. Eddrief, M. Marangolo, V. H. Etgens, H. Popescu and M. Sacchi, Thermally induced magnetization switching in Fe/MnAs/GaAs(001) : selectable magnetic configurations by temperature and field control, Scientific Rep. 5, 8120 (2015) https://hal.archives-ouvertes.fr/hal-01223188
- C. Spezzani, E. Ferrari, E. Allaria, F. Vidal, A. Ciavardini, R. Delaunay, F. Capotondi, E. Pedersoli, M. Coreno, C. Svetina, L. Raimondi, M. Zangrando, R. Ivanov, I. Nikolov, A. Demidovich, M. B. Danailov, H. Popescu, M. Eddrief, G. De Ninno, M. Kiskinova, and M. Sacchi, Magnetization and microstructure dynamics in Fe/MnAs/GaAs(001): Fe magnetization reversal by a femtosecond laser pulse, Phys. Rev. Lett. 113, 247202 (2014) https://hal.archives-ouvertes.fr/hal-01240513
- S. Günther, C. Spezzani, R. Ciprian, C. Grazioli, B. Ressel, M. Coreno, L. Poletto, P. Miotti, M. Sacchi, G. Panaccione, V. Uhlíř, E. E. Fullerton, G. De Ninno, and C. H. Back, Testing spin-flip scattering as a possible mechanism of ultrafast demagnetization in ordered magnetic alloys, Phys. Rev. B 90, 180407(R) (2014) https://hal.archives-ouvertes.fr/hal-01240508
