Revealing the Nature of the Ultrafast Magnetic Phase Transition in Ni by Correlating Extreme Ultraviolet Magneto-Optic and Photoemission Spectroscopies

You, Wenjing; Tengdin, Phoebe; Chen, Cong; Shi, Xun; Zusin, Dmitriy; Zhang, Yingchao; Gentry, Christian; Blonsky, Adam; Keller, Mark W.; Oppeneer, Peter M.; Kapteyn, Henry C.; Tao, Zhensheng; Murnane, Margaret M.

doi:10.1103/physrevlett.121.077204

Cited by 61 publications

(66 citation statements)

References 46 publications

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“…While in all-optical experiments, the dynamics are usually probed in reflection, implying that the dynamics are sampled with exponentially decreasing sensitivity into the bulk of the film; the entire film is probed in our transmission geometry. Our findings may therefore support recent considerations that the probing depth of the employed techniques should be taken into consideration 45 .…”

Section: Discussionsupporting

confidence: 90%

Single-shot time-resolved magnetic x-ray absorption at a free-electron laser

et al. 2019

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Ultrafast dynamics are generally investigated using stroboscopic pump-probe measurements, which characterize the sample properties for a single, specific time delay. These measurements are then repeated for a series of discrete time delays to reconstruct the overall time trace of the process. As a consequence, this approach is limited to the investigation of fully reversible phenomena. We recently introduced an off-axis zone plate based X-ray streaking technique, which overcomes this limitation by sampling the relaxation dynamics with a single femtosecond X-ray pulse streaked over a picosecond long time window. In this article we show that the X-ray absorption cross section can be employed as the contrast mechanism in this novel technique. We show that changes of the absorption cross section on the percent level can be resolved with this method. To this end we measure the ultrafast magnetization dynamics in CoDy alloy films. Investigating different chemical compositions and infrared pump fluences, we demonstrate the routine applicability of this technique. Probing in transmission the average magnetization dynamics of the entire film, our experimental findings indicate that the demagnetization time is independent of the specific infrared laser pump fluence. These results pave the way for the investigation of irreversible phenomena in a wide variety of scientific areas.

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Section: Discussionsupporting

confidence: 90%

Single-shot time-resolved magnetic x-ray absorption at a free-electron laser

et al. 2019

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“…We performed these simulations within the Microscopic Three Temperature Model (M3TM) 42 . We note that the limits of validity of M3TM are a matter of current investigation 50,69 particularly for timescales as short as we examine here, and thus, the demagnetization magnitudes we extract here should only be seen as a rough approximation of the true demagnetization that would occur. The equations governing the evolution of a sample within M3TM and neglecting spatial dependence for simplicity are 42,70 Here, is the electronic temperature, is the lattice temperature, and is the energy density deposited per unit time in the sample.…”

Section: Methodsmentioning

confidence: 89%

Femtosecond X-ray induced changes of the electronic and magnetic response of solids from electron redistribution

et al. 2019

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Resonant X-ray absorption, where an X-ray photon excites a core electron into an unoccupied valence state, is an essential process in many standard X-ray spectroscopies. With increasing X-ray intensity, the X-ray absorption strength is expected to become nonlinear. Here, we report the onset of such a nonlinearity in the resonant X-ray absorption of magnetic Co/Pd multilayers near the Co L edge. The nonlinearity is directly observed through the change of the absorption spectrum, which is modified in less than 40 fs within 2 eV of its threshold. This is interpreted as a redistribution of valence electrons near the Fermi level. For our magnetic sample this also involves mixing of majority and minority spins, due to sample demagnetization. Our findings reveal that nonlinear X-ray responses of materials may already occur at relatively low intensities, where the macroscopic sample is not destroyed, providing insight into ultrafast charge and spin dynamics.

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“…Here we employ nickel as a prototypical system and study the core-level TA spectra at the nickel M 2,3 edge around 67 eV to develop a framework to understand the core-level TA spectra of metals, extract the electron temperatures, investigate the carrier cooling dynamics, and explore electron thermalization. Nickel is a ferromagnetic material exhibiting sub-picosecond demagnetization when irradiated with a femtosecond laser pulse and has been extensively studied [8,19,21,30,35,38,[59][60][61][62][63][64][65]. Time-resolved photoemission measurements indicate that the photoexcited electrons in nickel thermalize on a sub-30-fs timescale [65] and electron-phonon relaxation times ranging from 200 fs to 1 ps have been derived from optical transient reflectivity and time-resolved second harmonic generation measurements [19,[59][60][61][62][63].…”

Section: Introductionmentioning

confidence: 99%

Electron thermalization and relaxation in laser-heated nickel by few-femtosecond core-level transient absorption spectroscopy

et al. 2021

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Direct measurements of photoexcited carrier dynamics in nickel are made using few-femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy at the nickel M 2,3 edge. It is observed that the core-level absorption line shape of photoexcited nickel can be described by a Gaussian broadening (σ ) and a red shift (ω s ) of the ground-state absorption spectrum. Theory predicts and the experimental results verify that after initial rapid carrier thermalization, the electron temperature increase ( T ) is linearly proportional to the Gaussian broadening factor σ , providing quantitative real-time tracking of the relaxation of the electron temperature. Measurements reveal an electron cooling time for 50 nm thick polycrystalline nickel films of 640 ± 80 fs. With hot thermalized carriers, the spectral red shift exhibits a power-law relationship with the change in electron temperature of ω s ∝ T 1.5 . Rapid electron thermalization via carrier-carrier scattering accompanies and follows the nominal 4-fs photoexcitation pulse until the carriers reach a quasithermal equilibrium. Entwined with a <6 fs instrument response function, carrier thermalization times ranging from 34 fs to 13 fs are estimated from experimental data acquired at different pump fluences and it is observed that the electron thermalization time decreases with increasing pump fluence. The study provides an initial example of measuring electron temperature and thermalization in metals in real time with XUV light, and it lays a foundation for further investigation of photoinduced phase transitions and carrier transport in metals with core-level absorption spectroscopy.

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Revealing the Nature of the Ultrafast Magnetic Phase Transition in Ni by Correlating Extreme Ultraviolet Magneto-Optic and Photoemission Spectroscopies

Cited by 61 publications

References 46 publications

Single-shot time-resolved magnetic x-ray absorption at a free-electron laser

Single-shot time-resolved magnetic x-ray absorption at a free-electron laser

Femtosecond X-ray induced changes of the electronic and magnetic response of solids from electron redistribution

Electron thermalization and relaxation in laser-heated nickel by few-femtosecond core-level transient absorption spectroscopy

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