Spin currents during ultrafast demagnetization of ferromagnetic bilayers

Eschenlohr, A.; Persichetti, Luca; Kachel, T.; Gabureac, Mihai; Gambardella, Pietro; Stamm, C.

doi:10.1088/1361-648x/aa7dd3

Cited by 33 publications

(19 citation statements)

References 33 publications

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“…As already suggested by Carva [24], "correctly" probing the magnetization might thus require an integration over the entire MCD spectrum (as intrinsically performed using broadband sources), and must be critically discussed in femtomagnetism experiments, where single, well-defined probing wavelengths are used. This could explain why several studies, despite using comparable experimental conditions, reported rather different characteristic demagnetization times [45][46][47] and significant differences concerning the onset of demagnetization in material systems composed of multiple elements [48][49][50].…”

Section: Discussionmentioning

confidence: 99%

Time-Resolved XUV Absorption Spectroscopy and Magnetic Circular Dichroism at the Ni M2,3-Edges

et al. 2020

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Ultrashort optical pulses can trigger a variety of non-equilibrium processes in magnetic thin films affecting electrons and spins on femtosecond timescales. In order to probe the charge and magnetic degrees of freedom simultaneously, we developed an X-ray streaking technique that has the advantage of providing a jitter-free picture of absorption cross-section changes. In this paper, we present an experiment based on this approach, which we performed using five photon probing energies at the Ni M2,3-edges. This allowed us to retrieve the absorption and magnetic circular dichroism time traces, yielding detailed information on transient modifications of electron and spin populations close to the Fermi level. Our findings suggest that the observed absorption and magnetic circular dichroism dynamics both depend on the extreme ultraviolet (XUV) probing wavelength, and can be described, at least qualitatively, by assuming ultrafast energy shifts of the electronic and magnetic elemental absorption resonances, as reported in recent work. However, our analysis also hints at more complex changes, highlighting the need for further experimental and theoretical studies in order to gain a thorough understanding of the interplay of electronic and spin degrees of freedom in optically excited magnetic thin films.

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Section: Discussionmentioning

confidence: 99%

Time-Resolved XUV Absorption Spectroscopy and Magnetic Circular Dichroism at the Ni M2,3-Edges

et al. 2020

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“…Optical spin-currents have been studied extensively in the last decade [5,[17][18][19][20][21][22][23][24][25][26][27]. However, the physics governing their generation and transport is still heavily debated.…”

mentioning

confidence: 99%

Probing optical spin-currents using THz spin-waves in noncollinear magnetic bilayers

Lichtenberg,

Beens,

Jansen

et al. 2021

Preprint

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Optically induced spin currents have proven to be useful in spintronics applications, allowing for sub-ps all-optical control of magnetization. However, the mechanism responsible for their generation is still heavily debated. Here we use the excitation of spin-current induced THz spin-waves in noncollinear bilayer structures to directly study optical spin-currents in the time domain. We measure a significant laser-fluence dependence of the spin-wave phase, which can quantitatively be explained assuming the spin current is proportional to the time derivative of the magnetization. Measurements of the absolute spin-wave phase, supported by theoretical calculations and micromagnetic simulations, suggest that a simple ballistic transport picture is sufficient to properly explain spin transport in our experiments and that the damping-like optical STT dominates THz spin-wave generation. Our findings suggest laser-induced demagnetization and spin-current generation share the same microscopic origin.

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“…In such composite systems, the interplay of charge and spin degrees of freedom between the different elements is not yet fully understood [10][11][12][13] . For example, tri-layer systems, in which spin currents are generated in an upper ferromagnetic (FM) layer and spread through a non-magnetic (NM) spacer towards a bottom FM layer, have been under intense investigation [14][15][16][17][18][19][20] . In a previous study, the observed enhancement of the magnetization of the bottom layer has been attributed to a superdiffusive current created in the top layer 15 .…”

mentioning

confidence: 99%

Simultaneous two-color snapshot view on ultrafast charge and spin dynamics in a Fe-Cu-Ni tri-layer

Rösner

Vodungbo

Chardonnet

et al. 2020

Structural Dynamics

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Ultrafast phenomena on a femtosecond timescale are commonly examined by pump-probe experiments. This implies multiple measurements, where the sample under investigation is pumped with a short light pulse and then probed with a second pulse at various time delays to follow its dynamics. Recently, the principle of streaking extreme ultraviolet (XUV) pulses in the temporal domain has enabled recording the dynamics of a system within a single pulse. However, separate pump-probe experiments at different absorption edges still lack a unified timing, when comparing the dynamics in complex systems. Here, we report on an experiment using a dedicated optical element and the two-color emission of the FERMI XUV free-electron laser to follow the charge and spin dynamics in composite materials at two distinct absorption edges, simultaneously. The sample, consisting of ferromagnetic Fe and Ni layers, separated by a Cu layer, is pumped by an infrared laser and probed by a two-color XUV pulse with photon energies tuned to the M-shell resonances of these two transition metals. The experimental geometry intrinsically avoids any timing uncertainty between the two elements and unambiguously reveals an approximately 100 fs delay of the magnetic response with respect to the electronic excitation for both Fe and Ni. This delay shows that the electronic and spin degrees of freedom are decoupled during the demagnetization process. We furthermore observe that the electronic dynamics of Ni and Fe show pronounced differences when probed at their resonance, while the demagnetization dynamics are similar. These observations underline the importance of simultaneous investigation of the temporal response of both charge and spin in multi-component materials. In a more general scenario, the experimental approach can be extended to continuous energy ranges, promising the development of jitter-free transient absorption spectroscopy in the XUV and soft X-ray regimes.

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Spin currents during ultrafast demagnetization of ferromagnetic bilayers

Cited by 33 publications

References 33 publications

Time-Resolved XUV Absorption Spectroscopy and Magnetic Circular Dichroism at the Ni M2,3-Edges

Time-Resolved XUV Absorption Spectroscopy and Magnetic Circular Dichroism at the Ni M2,3-Edges

Probing optical spin-currents using THz spin-waves in noncollinear magnetic bilayers

Simultaneous two-color snapshot view on ultrafast charge and spin dynamics in a Fe-Cu-Ni tri-layer

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