Capturing ultrafast magnetic dynamics by time-resolved soft x-ray magnetic circular dichroism

Abstract

Experiments of time-resolved x-ray magnetic circular dichroism (Tr-XMCD) and resonant x-ray scattering at a beamline BL07LSU in SPring-8 with a time-resolution of under 50 ps are presented. A micro-channel plate is utilized for the Tr-XMCD measurements at nearly normal incidence both in the partial electron and total fluorescence yield (PEY and TFY) modes at the L 2,3 absorption edges of the 3d transition-metals in the soft x-ray region. The ultrafast photo-induced demagnetization within 50 ps is observed on the dynamics of a magnetic material of FePt thin film, having a distinct threshold of the photon density. The spectrum in the PEY mode is less-distorted both at the L 2,3 edges compared with that in the TFY mode and has the potential to apply the sum rule analysis for XMCD spectra in pump-probed experiments.Control of electron, magnetic, and lattice states by optical excitations in magnetically ordered materials has attracted considerable attention due to their potential applications in electronic and magnetic recording media functioning on an ultrafast time scale below nanosecond (ns, 10 −9 second, GHz range), since the observation of the ultrafast demagnetization in Ni within 1 picosecond (ps). 1 The ultrafast photo-induced changes of magnetic states are non-equilibrium phenomena and several mechanisms have been proposed to understand them. 2-4 These phenomena generally involve fast structural changes near surface region 5,6 and therefore require cooperative effects, inevitably having a threshold of the photon density.To capture their non-equilibrium dynamics, ultrafast time-resolved experiments have been carried out using ultra-short laser pulses. 3 Recently, the development of a bunched synchrotron light source, 7-11 and x-ray free electron lasers 12-14 have enabled investigation of the dynamic phenomena with element selectivity by tuning the photon energy of the x-ray to the absorption edges of the constituent elements. Especially, time-resolved soft x-ray spectroscopy has many unique characteristics, such as element specificity, chemical specificity and surface sensitivity, which make them versatile for application in a wide range of scientific fields including spintronics and environmental science. Owing to its importance, various time-resolved soft x-ray spectroscopy studies have been carried out. [15][16][17][18][19][20][21] The time-resolved x-ray magnetic circular dichroism (Tr-XMCD) and resonant soft x-ray scattering (Tr-RSXS) measurements for magnetic and electronic materials have been conducted in LCLS, 13,14 ALS, 9 and BESSY II slicing facilities. 10,11,[15][16][17][18][19] The timeresolved x-ray magneto optical Kerr effect (XMOKE) measurements have also been conducted in FERMI. 12 Tr-XMCD measurements at the M absorption below hv <100 eV have also been performed by using high harmonics generation from tabletop lasers in recent years. 22 XMCD at the L 2,3 absorption of 3d transition-metals a) Electronic mail: ktakubo@issp.u-tokyo.ac.jp in the soft x-ray region (hv > 400 eV) is a powerful tool ...

Direct observation of the electronic states of photoexcited hematite with ultrafast 2p3d X-ray absorption spectroscopy and resonant inelastic X-ray scattering

“…Transient XAS spectra of the Fe L 3 edge in the picoseconds regime were measured at the BL07LSU beamline in SPring-8. 47 During the beamtime, the operation mode of SPring-8 was ''H-mode'', 48 where one electron bunch between bunch trains is detected. The X-rays from the isolated bunch arrives every B4.76 ms (B210 kHz).…”

Measurement of the Resonant Magneto-Optical Kerr Effect Using a Free Electron Laser

“…TR-XMCD is usually used in the L-edge range and is detected using a reflection geometry with grazing incidence [54]. There is also the possibility that out-of-plane magnetization dynamics may be detected using TR-XMCD in the L-edge range via transmission [3] and total fluorescence yield (TFY) [55] modes. However, for the transmission measurements, the sample thickness must be thin enough to allow high transmission, and the detection system for the TFY measurements must be carefully constructed to prevent the pump laser from entering the detectors and collecting a low photon flux.…”

Photo-induced Antiferromagnetic-ferromagnetic and Spin-state Transition in GdBaCo2O5.5 Thin Film

“…Ultrafast magnetic dynamics and transient magnetic states induced by optical excitation have attracted a lot of research interest [1][2][3][4][5][6][7][8][9][10]. Pioneered by the observation of the ultrafast demagnetization in Ni metal [1], the magnetic dynamics of various material systems are intensely investigated to characterize the important time scales related to the magnetic degree of freedom.…”

“…Pioneered by the observation of the ultrafast demagnetization in Ni metal [1], the magnetic dynamics of various material systems are intensely investigated to characterize the important time scales related to the magnetic degree of freedom. With the rapid development of synchrotron x-ray sources with pulsed time structures, the role of probe in pump-probe experiments can be played not only by optical lasers but also by synchrotron x-rays [3][4][5][6][7][8] or x-ray free electron lasers [9,10]. Synchrotron x-ray can provide multiple probing techniques with element specificity, such as x-ray magnetic circular dichroism (XMCD) [3,4,9], resonant magneto-optic Kerr effect [10] and resonant x-ray scattering [6][7][8], etc.…”

“…With the rapid development of synchrotron x-ray sources with pulsed time structures, the role of probe in pump-probe experiments can be played not only by optical lasers but also by synchrotron x-rays [3][4][5][6][7][8] or x-ray free electron lasers [9,10]. Synchrotron x-ray can provide multiple probing techniques with element specificity, such as x-ray magnetic circular dichroism (XMCD) [3,4,9], resonant magneto-optic Kerr effect [10] and resonant x-ray scattering [6][7][8], etc. Capturing the element-specific dynamic behaviors of not only ferromagnetic (FM) ordering, but also antiferromagnetic (AFM) ordering and complex magnetic structures become possible by employing synchrotronbased resonant magnetic x-ray diffraction (RMXD) [6][7][8], which cannot be realized by optical laser probes.…”