Structural dynamics during laser-induced ultrafast demagnetization

Jal, Emmanuelle; López‐Flores, Víctor; Pontius, N.; Ferté, Tom; Bergeard, Nicolas; Boeglin, C.; Vodungbo, Boris; Lüning, J.; Jaouen, N.

doi:10.1103/physrevb.95.184422

Cited by 27 publications

(26 citation statements)

References 46 publications

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“…Previous studies of magnetic structural dynamics were performed on continuous thin films deposited on substrates. [23][24][25] Our use of unconstrained FePt single-crystal nanoparticles allows us to study the full 3dimensional lattice motion on the natural timescale of the strain propagation through the nanoparticles. 26,27 This approach separates the individual contributions from electrons, spins, and phonons to lattice stress in FePt particles via their different symmetry properties and temporal onsets, as illustrated in Fig.1b.…”

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confidence: 99%

Beyond a phenomenological description of magnetostriction

et al. 2018

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Magnetostriction, the strain induced by a change in magnetization, is a universal effect in magnetic materials. Owing to the difficulty in unraveling its microscopic origin, it has been largely treated phenomenologically. Here, we show how the source of magnetostriction—the underlying magnetoelastic stress—can be separated in the time domain, opening the door for an atomistic understanding. X-ray and electron diffraction are used to separate the sub-picosecond spin and lattice responses of FePt nanoparticles. Following excitation with a 50-fs laser pulse, time-resolved X-ray diffraction demonstrates that magnetic order is lost within the nanoparticles with a time constant of 146 fs. Ultrafast electron diffraction reveals that this demagnetization is followed by an anisotropic, three-dimensional lattice motion. Analysis of the size, speed, and symmetry of the lattice motion, together with ab initio calculations accounting for the stresses due to electrons and phonons, allow us to reveal the magnetoelastic stress generated by demagnetization.

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confidence: 99%

Beyond a phenomenological description of magnetostriction

et al. 2018

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“…capping). Finally, XMRS experiments can be extended to time resolved experiments using synchrotron [11] or free electron laser [12], which should open new horizons to the exploration of the dynamics of magnetic chirality.…”

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confidence: 99%

Chirality in Magnetic Multilayers Probed by the Symmetry and the Amplitude of Dichroism in X-Ray Resonant Magnetic Scattering

et al. 2018

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Chirality is central to understand many fundamental mechanisms in various domains of physics and chemistry. In condensed matter, a large variety of physical phenomena hinge on the emergence of these complex chiral windings of order parameters, their observation and subsequently their control especially in magnetism and spintransport at the nanoscale. The ability to probe the nature of these chiral magnetic textures has now become a crucial element of modern magnetism and is therefore essential to gain a deeper understanding of these mechanisms. Spin-polarized scanning tunneling microscopy (SP-STM) revealed that magnetic textures with a cycloidal configuration of the magnetization and Néel domain walls are stabilized in ultra-thin magnetic films (one or a few atomic layers) on heavy metal substrates [1] . It was realized that these magnetic textures are stabilized by Dzyaloshinskii-Moriya (DM) interaction [2,3], (∑ 〈 〉• × , with Si and Sj two neighboring spins) which is the anti-symmetric analog of the Heisenberg interaction favoring a curling magnetization textures around the DM vector . The DM interaction requires spin-orbit coupling (SOC) and broken inversion symmetry, found either in specific crystalline structures, such as B20 materials [4], or at film interfaces [5,6].In this letter, we demonstrate that XRMS experiments (Figure 1a) allow us to reveal the actual magnetic textures existing in ultrathin magnetic multilayers with perpendicular anisotropy and large interfacial chiral interaction. Importantly, this determination is straightforward and does not require any assumptions or careful comparison to parameter-dependent micromagnetic simulations. Moreover, the circular dichroism in XMRS enables to identify directly not only the direction but also the sense of the magnetic winding and therefore of the actual sign of DM interaction as we proved by a thorough analysis. This information has a far-reaching impact in particular for spin-orbitronics and spin-orbit torque (SOT) studies. Indeed, SOT is a recent very promising approach to move efficiently domain walls [7] and magnetic skyrmions along magnetic race-tracks and shows therefore a great potential for future spintronic devices. Yet, the detailed texture of the domain walls plays a major role in their motion [8]: the DW high speed is related to its nature (Néel or Bloch) while its direction of motion depends on its chirality [7]. Besides, DM interaction can play an important role for existing technological applications in spintronics already using ultrathin magnetic multilayers with perpendicular magnetic anisotropy such as MRAM or detectors, in which the presence and the impact of non-negligible DM interaction has been largely overlooked (see e.g. [9,10]), emphasizing thus the need to probe its consequences on magnetic textures. XRMS presents several advantages that might soon turn it to a standard way to characterize and quantify the DM interaction. First, XMRS is a non-perturbative technique contrary to the approach based on magnetic domain analysis th...

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“… 30,31 It has recently been applied in pump–probe geometry to perform time-resolved XRMR (TR-XRMR) and study femtomagnetism. 32,33 While Gutt et al 33 have probed a magnetic trilayer film at the Fe

edge, showing a magnetic depth spatial resolution of tens of nanometer, applying this technique at L edges of transition metals will allow us to achieve a sub-nanometer magnetic spatial resolution. 30,31 In our previous work, 32 we performed a TR-XRMR experiment on a Ni thin film at the Ni L 3 edge.…”

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Toward ultrafast magnetic depth profiling using time-resolved x-ray resonant magnetic reflectivity

Chardonnet

Hennes

Jarrier

et al. 2021

Structural Dynamics

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During the last two decades, a variety of models have been developed to explain the ultrafast quenching of magnetization following femtosecond optical excitation. These models can be classified into two broad categories, relying either on a local or a non-local transfer of angular momentum. The acquisition of the magnetic depth profiles with femtosecond resolution, using time-resolved x-ray resonant magnetic reflectivity, can distinguish local and non-local effects. Here, we demonstrate the feasibility of this technique in a pump–probe geometry using a custom-built reflectometer at the FLASH2 free-electron laser (FEL). Although FLASH2 is limited to the production of photons with a fundamental wavelength of 4 nm ( ), we were able to probe close to the Fe L 3 edge ( ) of a magnetic thin film employing the third harmonic of the FEL. Our approach allows us to extract structural and magnetic asymmetry signals revealing two dynamics on different time scales which underpin a non-homogeneous loss of magnetization and a significant dilation of 2 Å of the layer thickness followed by oscillations. Future analysis of the data will pave the way to a full quantitative description of the transient magnetic depth profile combining femtosecond with nanometer resolution, which will provide further insight into the microscopic mechanisms underlying ultrafast demagnetization.

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Structural dynamics during laser-induced ultrafast demagnetization

Cited by 27 publications

References 46 publications

Beyond a phenomenological description of magnetostriction

Beyond a phenomenological description of magnetostriction

Chirality in Magnetic Multilayers Probed by the Symmetry and the Amplitude of Dichroism in X-Ray Resonant Magnetic Scattering

Toward ultrafast magnetic depth profiling using time-resolved x-ray resonant magnetic reflectivity

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