Couplage spin-electron-phonon-photon-structure

Magnétisme dans les architectures magnétiques

Classical Magnetic models : towards a multi-scale approach

Phenomenological magnetic models are able to bridge a gap between the microscopic magnetic properties and local organization of magnetic sites from a first part and the overall magnetic properties of bulk or nanosized materials from a second part.

In the case of Heisenberg model, the magnetic Hamiltonian is governed by few critical parameters, namely the magnetic moments of sites, the exchange energy between neighbors, the volume anisotropy constant and for finite size objects, the surface anisotropy constant and interface anisotropy constants.

Accuracy of the results emerging from the classical model is then intimately related to the theoretical or experimental determination of the underlying magnetic parameters and microscopic site organization of the system. This level of knowledge is not necessarily fulfilled in the case of complex structures or unusual compounds. Using a numeric multi-scale approach coupling ab-initio, molecular dynamics and Heisenberg simulations, access to a finer level of description. From one part the use of molecular dynamics simulation, permits to relax the structure of nano-sized or bulk systems and then to reproduce the magnetic sites position and distribution in a more realistic way. From another side, adjustments of ab-initio calculations and Heisenberg model on a large statistical sample of representative local environments allow us to determine the microscopic magnetic parameters.

Left: Influence of dopamine functionalization on magnetic properties. Right: Influence of structure relaxation on magnetic properties

Projects

ANR Obnarem

Publié le 8 mars 2022

Spin disorder versus Exchange bias coupling in magnetic nanoparticles with complex architecture (core/shell, Hollow, shell/shell, ...)

Researchers: Nader Yaacoub, Rodaina Sayed Hassan, Ivan Labaye, Jean-Marc Greneche

Collaboration: D. Peddis (INSTM nM2-Lab, Universita degli Studi diGenova), S. Ammar (ITODYS, Paris)

Magnetic nanoparticles (MNPs) are of particular interest in the field of information storage and nanomedicine (hyperthermia, medical imaging, …). Thanks to their nanometric size, they can be guided using a magnetic field. Unfortunately, reducing the size of nanomagnets leads to magnetic instability (superparamagnetic) that is incompatible with technological applications. Modifying the shape of the MNPs (core-shell MNPs, Hollow MNPs, …) leads to an exaltation of surface/interface effects (spin disorder, exchange bias (EB) coupling, …) and an increase of the magnetic anisotropy. Although the macroscopic model of the EB effect has existed for nearly six decades, the microscopic origin of this phenomenon is still requiring further investigation in some specific nanoscale systems. A complete understanding of the correlation between spin structure, surface/interface effect, collective behavior and EB coupling is still lacking. In this context, we are studying this phenomenon in systems with different architectures from an experimental and numerical point of view. For example, using in-field Mössbauer spectrometry and numerical simulation, we have shown the existence of complex non-collinear magnetic structure in hollow iron oxide MNPs. Indeed, this structure consists of a ferrimagnetic layer of a few atomic planes confined between two layers with canted structure resulting from two antiferromagnetic coupled speromagnetic structures (figure below). Such a magnetic structure leads to an increase of the magnetic coupling between the interfacial moments of the magnetic phases and in definitive the magnetic stability of the nanostructure. We propose to extend this study to systems presenting high spin disorder, such as hollow NPs with different sizes and shell thicknesses and to shell/shell systems, that consist of two magnetic phases: a ferrimagnetic phase and an antiferromagnetic one, while taking in consideration the effect of dipolar interaction on spin disorder and EB. In addition, it was concluded from Mössbauer characterization and computer modeling that octahedral Fe units are preferentially located at the surface compared to tetrahedral units (to be published).

Properties of hollow magnetic nanoparticles

Related recent papers:

[1] G. Muscas, F. Congiu, G. Concas, C. Cannas, V. Mameli, N. Yaacoub, R. Sayed Hassan, D. Fiorani, S. Slimani and D. Peddis. The Boundary Between Volume and Surface-Driven Magnetic Properties in Spinel Iron Oxide Nanoparticles.
Nanoscale Research Letters, 2022, 17, 98.

[2] D. Peddis, K. N. Trohidou, M. Vasilakaki, G. Margaris, M. Bellusci, F. Varsano, M. Hudl, N. Yaacoub, D. Fiorani, P. Nordblad & R. Mathieu.
Memory and superposition in a superspin glass.
Scientific Reports, 2021, 11, 7743.

[3] S. Slimani, G. Concas, F. Congiu, G. Barucca, N. Yaacoub, A. Talone, M. Smari, E. Dhahri, D. Peddis, and G. Muscas.
Hybrid Spinel Iron Oxide Nanoarchitecture Combining Crystalline and Amorphous Parent Material.
Phys. Chem. C, 2021, 125, 10611.

[4] M. Ghoshani, E. H. Sánchez, S. S. Lee, G Singh, N. Yaacoub, D. Peddis, M. Mozaffari, C. Binns, J. A. De Toro and P. S. Normile.
On the detection of surface spin freezing in iron oxide nanoparticles and its long-term evolution under ambient oxidation.
Nanotechnology, 2020, 32, 065704.

[5] G. Franceschin, T. Gaudisson, S. Perez Quiros, N. Yaacoub, J-M. Greneche, N. Menguy, S. Mercone, F. Mazaleyrat and S. Ammar.
Exchange-bias features in nanoceramics prepared by spark plasma sintering of exchange-biased nanopowders.
Mater. Chem. C, 2020, 8, 5941.

[6] N. Flores-Martinez, G. Franceschin, T. Gaudisson, S. Haj-Khlifa, S. Gam Derouich, N. Yaacoub, J-M. Grenèche, N. Menguy, R. Valenzuela & S. Ammar.
On the first evidence of exchange bias feature in magnetically contrasted consolidates made from CoFe2O4-CoO core-shell nanoparticles.
Scientific reports, 2019, 9, 19468.

[7] Z. Nehme, Y. Labaye, N. Yaacoub, J.-M. Grenèche
An atomic scale Monte Carlo study of exchange bias in homogeneous/inhomogeneous core/shell Fe3O4/CoO nanoparticles
Nanopart. Res., 2019, 21, 209.

[8] N. Yaacoub, H. Mortada, Z. Nehme, J.-M. Greneche
Chemical Inhomogeneity in Iron Oxide@ CoO Core–Shell Nanoparticles: A Local Probe Study Using Zero-Field and In-Field 57Fe Mössbauer Spectrometry.
Journal of nanoscience and nanotechnology, 2019, 19, 5014.

[9] G. Franceschin, T. Gaudisson, N. Menguy, B. C. Dordill, N. Yaacoub, J.-M. Greneche, R. Valenzuela, S. Ammar.
Exchange‐Biased Fe_3−xO₄‐CoO Granular Composites of Different Morphologies Prepared by Seed‐Mediated Growth in Polyol: From Core–Shell to Multicore Embedded Structures.
Part. Part. Syst. Charact., 2018, 35, 1800114.

[10] N. Flores-Martinez, G. Franceschin, T. Gaudisson, P. Beaunier, N. Yaacoub, J.-M. Greneche, R. Valenzuela, S. Ammar.
Giant exchange-bias in polyol-made CoFe₂O₄-CoO core-shell like nanoparticles.
Part. Part. Syst. Charact., 2018, 35, 1800290.

[11] F. Sayed, N. Yaacoub, Y. Labaye, R. Sayed Hassan, G. Singh, P. Anil Kumar, J.-M. Greneche, R. Mathieu, G. C. Hadjipanayis, E. Agostinelli, D. Peddis.
Surface Effects in Ultrathin Iron Oxide Hollow Nanoparticles: Exploring Magnetic Disorder at the Nanoscale.
Phys. Chem. C, 2018, 122, 7516.

[12] M. Vasilakaki, G. Margaris, D. Peddis, R. Mathieu, N. Yaacoub, D. Fiorani, and K. Trohidou.
Monte Carlo study of the superspin glass behavior of interacting ultrasmall ferrimagnetic nanoparticles.
Phys. Rev. B, 2018, 97, 094413.

Projects:

ANR OBNAREM (2014 – 2018)

PICS France – Italy (2014 – 2017)

Publié le 8 janvier 2024

Multiferroic Materials

Multiferroic materials constitute a class of multifunctional materials presenting in the same time coupled properties in terms of ferromagnetic-ferroelectric and ferroelastic order. On a fundamental scale, the nature of the interactions and in particular the magnetoelastic coupling mechanism is not fully understood despite the amount of experiments. On a technological level, this class of material is interesting in the field of information storage or for microelectromechanical systems development. Among multiferroic materials, BiFeO₃is one is one of the few which presents in the same time both ferroelectric and magnetic order above 300K. However despite this unique property, BiFeO₃also presents a magnetic helicoïdal structure of Fe³⁺ magnetic moments, this magnetic structure leads to weak magnetoelectric coupling. A drastic increase of magnetoelectric coupling can be obtained through the breakdown of helicoïdal spirale and the formation of an antiferromagnetic linear structure of type G leading to a non-zero mean magnetization.

Multiples ways can be followed to breakdown this helicoidal structure among them:

Reducing the size of the material dimension to a value lower than the cycloid period (~64 nm). This can be obtained by a polyol method for synthetizing BiFeO₃ nanoparticles.
Substituting Bi³⁺ and Fe³⁺ by Ti⁴⁺ and Zr⁴⁺ using a ceramic synthesis in order to partially break helicoïdal structure of Fe³⁺ magnetic moments

MEB picture of BiFeO3 particles obtained with polyol processModification of helicoïdal magnetic order and apparition of ferromagnetic order

Publié le 8 mars 2022

Rare Earth Free Permanent Magnets

Researchers: Nirina Randrianantoandro, Rodaina Sayed Hassan, Florent Calvayrac, Nader Yaacoub

Collaboration: A. Bajorek (INPM – Roumania), D. Peddis (INSTM nM2-Lab, Universita degli Studi diGenova), R. Awad (Beirut Arab University, Department pf physics).

Permanent magnets (PMs) are fundamental components in a wide variety of applications. Current high-performance PMs owe their extraordinary properties to the presence of rare-earth (RE) elements, which allows reaching a maximum energy product (BH)max as high as 0.5 MJ/m³ at room temperature in Nd-Fe-B compounds. However, despite their very high performances, RE-PMs present important drawbacks, such as high costs, serious environmental impact, … . To avoid the strong environmental and economic impact of the RE industry, an intense research activity has been carried out to develop effective solutions that allow reducing the demand of RE elements, including the optimization of existing materials and magnets design, the development of new hard magnetic phases. Ferromagnetic τ-MnAl is a promising candidate among RE-free PMs currently being researched due to its intrinsic magnetic properties. Mn(Fe)AlC was synthesized and the effects of carbon on microstructure and magnetic properties were systematically investigated. It was found that high purity of τ-MnAl(C) could be obtained at 2 at.% C doping, showing clearly stabilizing effect of carbon. Mn_54.2Al_43.8C₂ has the best magnetic properties: magnetization at 2T M_2T = 414 kA.m^-1, remanent magnetization M_r = 237 kA.m^-1, coercivity H_C = 229 k.Am^-1, and |BH|_max = 11.2 kJ.m^-3. Moreover, first principle calculation showed both stabilizing effect and preferable interstitial positions of carbon in tetragonal τ-MnAl. Mn_51-xFe_xAl₄₇C₂ alloys were also synthesized, showing the high purity of τ phase up to 2 at.% Fe doping. Adding of Fe on MnAl(C) reduced both magnetization and T_C but likely increased slightly H_C. The interaction between Fe and Mn examined by in-field ⁵⁷Fe Mössbauer measurement at 10 K and 8 T showed a non-collinear magnetic structure between Fe and Mn with different canting angles at different sites. Hyperfine field of MnFeAl alloy calculated by Wien2k supported both magnetic properties and Mössbauer results. Among the different approaches proposed so far to maximize the (BH)max of RE-free PMs, a lot of attention has been paid towards nanostructured hybrid materials based on the coupling of a hard and a soft magnetic material. In this context, we are studying this phenomenon in ferrite-based nanocomposites consisting of a hard SrFe₁₂O₁₉ (SFO) (SFO has received large attention owing to its chemical stability, large availability, low production cost and good magnetic properties (saturation magnetization M_S = 70–72 Am² kg⁻¹, coercivity H_C = 400 kA m⁻¹ and (BH)max close to 40 kJ. m⁻³)) or SFO doped phase exchange-coupled with a softer spinel ferrite with different architectures.

Related recent papers

[1] Varvaro, P. Imperatori, S. Laureti, D. Peddis, F. Locardi, M. Ferretti, C. Cannas, M. Sanna Angotzi, N. Yaacoub, A. Capobianchi.
Facile and fast synthesis of highly ordered L10-FeNi nanoparticles
Scripta Materialia, 2024, 238, 115754.

[2] T. Nguyen, F. Mazaleyrat, N. Randrianantoandro
Investigation of Mn-Fe magnetic interaction in mechanically alloyed Fe doped-MnAlC by ⁵⁷Fe Mossbauer ¨ spectrometry
Mag. Mag. Mat., 2023, 568, 170437.

[3] Maltoni, M. Baricic, G. Barucca, M C Spadaro, J. Arbiol, N. Yaacoub, D. Peddis and R. Mathieu.
Tunable particle-agglomeration and magnetic coupling in bi-magnetic nanocomposites.
Phys. Chem. Chem. Phys., 2023, 25, 27817.

[4] Maltoni, G. Barucca, B. Rutkowski, M C. Spadaro, P E. Jönsson, G. Varvaro, N. Yaacoub, J A. De Toro, D. Peddis and R. Mathieu.
Unraveling Exchange Coupling in Ferrites Nano-Heterostructures.
Small, 2023, 2304152.

[5] Muzzi, E. Lottini, N. Yaacoub, D. Peddis, G. Bertoni, C. de Julián Fernández, C. Sangregorio, and A. López-Ortega
Hardening of Cobalt Ferrite Nanoparticles by Local Crystal Strain Release: Implications for Rare Earth Free Magnets
ACS Appl. Nano Mater., 2022, 5, 14871.

[6] Rifai, F. Fattouh, K. Habanjar, N. Yaacoub, R. Awad.
Exchange spring behaviour in BaFe₁₂O₁₉/CoFe₂O₄ magnetic nanocomposites.
Journal of Alloys and Compounds, 2021, 868 ,159072.

[7] Fattouh, L. Rifai, K. Habanjar, A. M. Abdallah, R. Sayed Hassan, N. Yaacoub and R. Awad
Structural and magnetic properties of hard-soft BaFe₁₂O₁₉/(Zn_0.5Co_0.5)Fe₂O₄ ferrites
Phys.: Condens. Matter, 2021, 33 ,235803.

[8] T. Nguyen, F. Mazaleyrat, F. Calvayrac, Quang Minh Ngo, N. Randrianantoandro
Investigation on magnetic properties of mechanically alloyed τ-MnAlC with Fe addition
Mag. Mag. Mat., 2021, 546, 168892.

[9] Petrecca, B. Muzzi, S. Maria Oliveri, M. Albino, N. Yaacoub, D. Peddis, C. d. J. Fernandez, C. Innocenti and C. Sangregorio.
Optimizing the magnetic properties of hard and soft materials for producing exchange spring permanent magnets.
Phys. D: Appl. Phys., 2021, 54 ,134003.

[10] T. Nguyen, F. Calvayrac, Anna Bajorek, N. Randrianantoandro
Mechanical alloying and theoretical of MnAl(c) magnets
Mag. Mag. Mat., 2018, 462, 96.

Projects:

PHC BRANCUSI 2019 – 2022.

Publié le 8 janvier 2024

Dynamique ultra-rapide photo-induite et optique non linéaire

Simulation of ultrafast phenomena

Researchers

Brice Arnaud
Rémy Busselez
Florent Calvayrac

Electron and phonon dynamics in photoexcited solids

Schematic view of relaxation processes in photoexcited siliconPump probe experiments like optical pump probe experiments, time resolved X-ray diffraction, or time resolved photoemission experiments are currently used to study electron and phonon dynamics in nanostructures on time scales ranging from a few femtoseconds to a few picoseconds. Among the aforementioned techniques, optical pump probe experiments allow to study the coherent phonon generation mechanisms or even the possibility to demagnetize a sample with an ultrashort laser pulse. It is often difficult to interpret experimental results without resorting to models whose parameters can be inferred from ab-initio calculations. There are few calculations because of the need to describe non-equilibrium phenomenon occurring on different time scales and length scales. Nonetheless, ab-initio calculations combined with models already shed new light on ultrafast physics, especially on the coherent phonon generation, on the non thermal melting processes or on the energy transfer from the electronic degrees of freedom to the the vibrational degrees of freedoms.

Related papers

Isabel González Vallejo, Geoffrey Gallé, Brice Arnaud, Shelley A. Scott, Max G. Lagally, Davide Boschetto, Pierre-Eugene Coulon, Giancarlo Rizza, Florent Houdellier, David Le Bolloc’h, and Jerome Faure, “Observation of large multiple scattering effects in ultrafast electron diffraction”, Phys. Rev. B 97, 054302 (2018).

TDDFT approaches to compute excited states of finite systems

The PW-TELEMAN project aims at developing an open source (under GPL3) and easy accessible package of real-time TDDFT libraries and codes, based on programs developed over the past 20 years in a Toulouse-Erlangen collaboration which spread to Le Mans and China via former students. At the time being no available code truly accounts for a complete non-adiabatic electron-ions coupling allowing a full follow-up of a whole dynamical scenario from early excitation (fs or sub-fs) to long time response (ps) of a given physical system. To the best of our knowledge, the Toulouse-Erlangen package is one of the single ones allowing such an investigation in a fully time-resolved manner. Still this package requires a strong effort of standardization and documentation and in order to make it more efficient and usable by external groups. More optimization is highly desirable to exploit the latest computer technology such as GPGPU and so to access the much more demanding tasks in organic molecules. It is the goal of the project to succeed in these two complementing directions.

The variety of potential applications is obvious. We mention in particular the very practical aspects concerning irradiation of biological molecules and radiation damage in materials. The plan is to develop our project in two complementing directions: first, implementation and tests of formal developments such as approximations to TDSIC/OEP methods, coupled with an exploration of various dynamical scenarios of increasing complexity (requiring ongoing optimization), starting with free molecules and clusters, turning to systems such as a chromophore cluster embedded in a matrix, ending with a coupled quantum mechanics/molecular mechanics hierarchical modeling of a biophysical problem made possible due to the expected increase in numerical performance and on the other hand standardization, documentation, and publication of a toolbox of routines which will be easily usable by other groups.

Benchmark of PW-Teleman code, Efficiency versus core number for differents architecture optimisation

Projects

ANR Teleman

Publié le 22 décembre 2023

Electron and phonon ultrafast dynamic in solid exhibiting exotic coupling between charge, spin and structure

Researchers

Brice Arnaud
Rémi Busselez
Marwan Deb
Mathieu Edely
Vincent Juvé
Pascal Ruello
Gwenaëlle Vaudel
Mads Weber
Coll. B. Dkhil, C. Paillard, SPMS Centrale Supelec, V. Garcia, S. Fusil, UMPhy Thales, C. Laulhé LPS-Univ. Paris-Saclay, D. Sando, Univ. Canterbury (New Zealand), H. Bouyanfif LPMC Univ Picardie, L. Bellaiche Univ Arkansas (USA), L. Yedra, Univ. Barcelona (Spain), J. Szade, K. Balin, Institute of Physics, Katowice (Poland).

Ultrafast photostriction in ferroelectrics and multiferroics

The control of the photoinduced coherent acoustic phonon in ferroelectric and multiferroic compounds have been investigated in order to investigate the electron-phonon coupling and the coherent acoustic phonon detection processes. This research has permitted to reveal an original ultrafast optical-light mode conversion in BiFeO3 and LiNbO3. We have shown that it was possible to switch the light polarization from the ordinary to the extraordinary component (and vice-versa) with coherent acoustic phonon and this, up to hundreds of GHz (10ps). This mechanism is based on the modulation of the birefringence of the uniaxial crystal (BiFeO₃, LiNbO₃) induced, through the acousto-optic effect, by the coherent acoustic phonons (left panel in the figure below) [1]. This work has been selected by INP CNRS as a “highlight” [2]. This research is still going on with a focus on new possible way to generate acoustic phonon [3] (transformation of light energy into mechanical energy) with an ANR project UP-DOWN (IMMM leader) that has started in October 2018. The extension of the coupling between coherent acoustic phonons with the magnetic order and in particular with antiferromagnons will be investigated in the ANR SANTA (SPEC-CEA Leader) that has started in October 2018 as well.

Ultrafast light-mode conversion in birefringent ferrolectric materialsUltrafast electron and phonon dynamics in Topological insulators

Related papers

Temporal and spatial tracking of ultrafast light-induced strain and polarization modulation in a ferroelectric thin film, Ruizhe Gu, Vincent Juvé, Claire Laulhé, Houssny Bouyanfif, Gwenaëlle Vaudel, Aurélie Poirier, Brahim Dkhil, Philippe Hollander, Charles Paillard, Mads C Weber, Daniel Sando, Stéphane Fusil, Vincent Garcia, Pascal Ruello, Science Advances 9 (46), eadi1160 (2023)
Optical absorption by design in a ferroelectric: co-doping in BaTiO 3
S Hao, M Yao, G Vitali-Derrien, P Gemeiner, M Otoničar, P Ruello, Housnny Bouyanfif, Pierre-Eymeric Janolin, Brahim Dkhil, Charles Paillard
Journal of Materials Chemistry C 10 (1), 227-234 (2022)
Nonthermal Transport of Energy Driven by Photoexcited Carriers in Switchable Solid States of R Gu, T Perrault, V Juvé, G Vaudel, M Weis, A Bulou, N Chigarev, A Levchuk, S Raetz, VE Gusev, Z Cheng, H Bhaskaran, P Ruello
Physical Review Applied 16 (1), 014055 (2021)
Ultrafast light-induced shear strain probed by time-resolved x-ray diffraction: Multiferroic as a case study
V Juvé, R Gu, S Gable, T Maroutian, G Vaudel, S Matzen, N Chigarev, Samuel Raetz, VE Gusev, M Viret, A Jarnac, C Laulhé, AA Maznev, B Dkhil, Pascal Ruello
Physical Review B 102 (22), 220303 (2020)
Magnetoelastic and magnetoelectric couplings across the antiferromagnetic transition in multiferroic
M Lejman, C Paillard, V Juvé, G Vaudel, N Guiblin, L Bellaiche, M Viret, Vitalyi E Gusev, Brahim Dkhil, Pascal Ruello
Physical Review B 99 (10), 104103 (2019)
Evaluation of the Structural Phase Transition in Multiferroic (Bi1−x Prx)(Fe0.95 Mn0.05)O3 Thin Films by A Multi-Technique Approach Including Picosecond Laser Ultrasonics
S Raetz, A Lomonosov, S Avanesyan, N Chigarev, E de Lima Savi, Alain Bulou, Nicolas Delorme, Zheng Wen, Qiao Jin, Maju Kuriakose, Anthony Rousseau, Gwenaëlle Vaudel, Pascal Ruello, Di Wu, Vitalyi Gusev
Applied Sciences 9 (4), 736 (2019)

Ultrafast acousto-optic mode conversion in optically birefringent ferroelectrics, Mariusz Lejman, Gwenaelle Vaudel, Ingrid C Infante, Ievgeniia Chaban, Thomas Pezeril, Mathieu Edely, Guillaume F Nataf, Mael Guennou, Jens Kreisel, Vitalyi E Gusev, Brahim Dkhil, Pascal Ruello, Nature comm. 7, 12345 (2016)

http://www.cnrs.fr/inp/spip.php?article4895

Photothermal optomechanics, P Ruello, Nature Photonics 10 (11), 692 (2016).

Projects

ANR THz-MUFINS (ANR-21-CE42-0030)
Lmac Région Pays de la Loire (Ferrotransducteur 2015-2019)
ANR UP-DOWN 2018-2021

Ultrafast electron and phonon dynamics in topological insulators

In this work we have investigated ultrathin films of topological insulator (4-15nm). We have first studied the influence of the substrate and the microstructure (single versus polycrystalline structure on the femtosecond pulse-induced electron and phonon dynamics. While the optical phonons (zero group velocity) have frequency and damping dynamics nearly unaffected, the acoustic phonon signature (propagating wave) is clearly different revealing the importance of acoustic phonon scattering on grains boundaries and at interface between the nanometric film and the substrate [1]. In a second study, we have in particular measured the dynamic of hot carriers in Bi₂Te₃ compound and have shown the existence of a strong quantum confinement appearing for thickness as thin as 5-6nm. A dramatic enhancement of the hot carriers relaxation is observed (right panel in the figure above). Such quantum confinement is also revealed in a thickness dependence of the process of generation of coherent acoustic phonons and in the anomalous damping of a Raman active mode A1g mode, together with a slight A1g mode softening. These phenomena evidence a drastic evolution of the electron-phonon coupling in a highly confined system. We have proposed with a simple model, that the band gap increases with decreasing the thickness is an indication of the increase of the electron-longitudinal acoustic phonon deformation potential. A more advanced theoretical work is now required to extract a more precise microscopic picture. Nevertheless, these experimental results are important to tailor the proper thickness of such material for future integration in more complex devices where for example spin-to-charge conversion will be investigated.

Projects

French-Polish project, Bourse Ambassade de France (M. Weis), thèse co-tutelle (Le Mans, Insttut de Physique Katowice).

Publié le 14 décembre 2023

Ultrafast terahertz spectroscopy

Researchers

Brice Arnaud
Rémi Busselez
Vincent Juvé
Pascal Ruello
Gwenaëlle Vaudel
Mads Weber
Coll. JY CHauleau, M. Viret, CEA-SPEC, J. Szade Institute of Physics Katowice (Poland), Laboratoire International Associé CNRS, France-Japon (LIA-IM-LED)

THz polarization modulation of visible light by THz pulses

Over the last decade, ultrafast Terahertz spectroscopy has gained tremendous attention thanks to the development of high-power ultrafast laser systems, which allowed generating intense single-cycle picosecond pulses of electric field at THz frequencies. Their relatively long optical cycle period (1 ps for 1 THz) and high electric field (from hundred of kV/cm to few MV/cm) provide a new tool for studying fundamental aspects of light-matter interactions. Field-resolved detection of ultra-short THz pulses is well known since many years and the most common technique is based on free-space electro-optic sampling. This leads to the polarization change of an optical pulse, which is detected by the polarization sensitive scheme, and to the field-resolved detection of a THz pulse. Here we evidenced efficient non-resonant and noncollinear χ⁽²⁾-type type light-matter interaction in femtoseconds polarization sensitive time-resolved optical measurements. Such nonlinear optical interaction of visible light and ultra-short THz pulses leads to THz modulation of visible light polarization in bulk LiNbO₃ crystal. Theoretical simulations based on the wave propagation equation capture the physical processes underlying this nonlinear effect [1].

Left: A femtosecond optical pulse and a THz pulse, delayed in time respect to each other, are overlapping in a LiNbO3 crystal. Right: Non-resonant and noncollinear χ(2)-type light-matter interaction leads to a rotation Δθ of the optical pulse polarization at THz frequencies

Projects

Région Pays de la Loire (Pari Scientifique NanoPlasmag 2018-2021)
ANR SANTA 2018-2021

Ultrafast THz emission by spin to charge current conversion (ferroic materials and topological insulators)

Topological insulators (Bi₂Se₃, Bi₂Te₃ etc…) are a new class of material, which is stated to be at the core of the next generation of electronics devices. Their structure consists of a bulk small bandgap insulator together with spin polarized surface states, which can lead to surface spin current. Studying and controlling the surface spin current is of interest for the scientific community. Using ultrafast THz spectroscopy, with photon energy smaller than the band gap, one can try to have access to the surface states dynamics and, thus, to the spin dynamics. High quality samples, which are well characterized of Bi₂Te₃, are provided by the University of Silesia in Poland [1].

Left: Simplified band structure of topological insulators, which consists of a combination of a small band gap together with spin-polarized Dirac cones. Right: Relative change of the transmission induced by a THz pulse (2 meV photon energy) measured with a 3.1 eV photon energy for a Bi2Te3 sample of 15nm thickness.

We also have started to investigate the emerging field related to spin-to-chareg conversion (vice-versa). spin bursts can be produced by direct excitation of hot electrons in a ferromagnetic layer triggered by a femtosecond laser pulse. During the relaxation processes the diffusion lifetime and mobility differ for majority and minority spin carriers, resulting in the emission of angular momentum on a timescale of picoseconds. This effect, combined with Inverse Spin Hall Effect in an adjacent non-magnetic layer (Pt), was recently used to make efficient THz generation devices [2]. Based on this principle, we have already carried out preliminary measurement with CoFeB on Pt by shining femtosecond laser pulses to inject spin current bursts. As the direction of spin current is determined by the magnetization of the Ferromagnetic, the mechanism provides an easy and efficient way of controlling the direction of spin torque with a small magnetic field. This project is part of the Santa ANR (2018-2021) lead by Michel Viret (CEA/SPEC) within which IMMM is involved (starting Oct 2018).

Left: Principle of the spin to charge current conversion leading to THz emission (taken from Seifert et al Nat. Phot. 2016). Right: Ultrafast THz emission measured by electro-optic sampling after ultrafast photoexcitation in a FeCoB(5nm)/Pt(3nm) sample. Reversing the external magnetic field leads to a change of sign of the THz electric field.

Related papers

Pump wavelength-dependent terahertz spin-to-charge conversion in CoFeB/MgO Rashba interface, Artem Levchuk, Vincent Juvé, Tadele Orbula Otomalo, Théophile Chirac, Olivier Rousseau, Aurélie Solignac, Gwenaëlle Vaudel, Pascal Ruello, Jean-Yves Chauleau, Michel Viret, Applied Physics Letters 123 (1) (2023)
Coherent acoustic phonons generated by ultrashort terahertz pulses in nanofilms of metals and topological insulators
A Levchuk, B Wilk, G Vaudel, F Labbé, B Arnaud, K Balin, J Szade, P Ruello, V Juvé
Physical Review B 101 (18), 180102 (2020)
[1] V. Juvé et al, in preparation
[2] T. S. Seifert, N. M. Tran, O. Gueckstock, S. M. Rouzegar, L. Nadvornik, S. Jaiswal, G. Jakob, V. V. Temnov, M. Münzenberg, M. Wolf, M. Kläui and T. Kampfrath. J. Phys. D Appl. Phys. (2018)

Projects

Région Pays de la Loire (Pari Scientifique NanoPlasmag 2018-2021)
ANR SANTA 2018-2021

Publié le 22 décembre 2023

Ultrafast Control of Magnetism

Researchers

Marwan Deb
Vincent Juvé
Pascal Ruello
Gwenaëlle Vaudel
Mads Weber
Nirina Randrianantoandro

Controlling the magnetization at the fastest speed and with the lowest energy is one of the hottest topics in modern magnetism. It requires a deep understanding of the interaction between spin, electron, and lattice and their response to an external stimulus. Our research aims to address new frontiers in this topic by exploring novel magnetic materials and using various types of ultrashort external stimuli, including femtosecond laser pulses, femtosecond hot-electron pulses, picosecond acoustic pulses, as well as electric field. The nanoscale physics resulting from the interaction of these functionalities with suitable magnetic materials allows us to exploit non-thermal excitation mechanisms based on photo- and opto-magnetic effects, magnetoelastic effects, spin-transfer torque, and magneto-electric coupling to induce several important phenomena, such as spin-waves and magnetic-field-free magnetization switching. We study this rich physics with the help of new experimental approaches enabling both static and time-resolved measurements with sub-picosecond resolution. This research at the interface between magneto-electrics, femto-magnetism, pico-magneto-acoustic, and femto-spintronics should advance the fundamental knowledge, with potential implications for technological applications.

Projects

ANR ULTRAMAG
UNCLOAK

Publié le 22 décembre 2023

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Couplage spin-electron-phonon-photon-structure