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Team
- Permanent members: Maurizzio Sacchi, Stéphane Chenot, Mahmoud Eddrief, Franck Vidal, Yunlin Zheng
- Recent thesis: Lounès Lounis
- Invited: Leticia Coelho
Epitaxy allows the control of the magnetic properties of thin film systems and the development of new hybrid heterostructures. Our research focuses on systems integrating magneto-structural phase transition materials that allow the development of magnetization control strategies without a magnetic field. From a more fundamental point of view, the phase transition mechanisms in these systems with strong coupling between structural and magnetic degrees of freedom are also the subject of detailed studies. These are largely based on the opportunities offered by X-FELs, the latest generation X-ray sources.
The following lines of research are currently being explored:
- Non inductive reversal of the magnetization. Preparation and characterization of hybrid magnetic systems based on MnAs [1-4] and FeRh [5,6]. The reversal of the magnetization of an additional layer (Fe or Co) can be obtained by controlling the surface dipole field, either thermally [2], or by the absorption of a single laser fs pulse [1 ]. 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 [3,4].
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 [4]. 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 [3].
Highlight
Principal collaborations
- LCPMR (SU)
- Synchrotron SOLEIL
- Sincrotrone Trieste
Recent publications
- C. Spezzani et al., 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
- C. Spezzani, et al., 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
- L. Lounis et al., 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
- F. Vidal et al., 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
- S. Günther et al., Testing spin-flip scattering as a possible mechanism of ultrafast demagnetization in ordered magnetic alloys, Rev. B 90, 180407(R) (2014).https://hal.archives-ouvertes.fr/hal-01240508
- L. Lounis et al., Temperature and field dependent magnetization in a sub-μm patterned Co/FeRh film studied by resonant x-ray scattering. Phys. D : Appl. Phys. 49, 205003 (2016).https://hal.sorbonne-universite.fr/hal-01323817
