Table Of ContentCapturing ultrafast magnetic dynamics by time-resolved soft x-ray magnetic
circular dichroism
Kou Takubo,1,a) Kohei Yamamoto,1 Yasuyuki Hirata,1 Yuichi Yokoyama,1 Yuya Kubota,1 Shingo Yamamoto,1
Susumu Yamamoto,1 Iwao Matsuda,1 Shik Shin,1 Takeshi Seki,2 Koki Takanashi,2 and Hiroki Wadati1
1)Institute for Solid State Physics, University of Tokyo, Kashiwanoha 5-1-5, Chiba 277-8581,
Japan
2)Institute for Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-8577,
Japan
(Dated: 13 January 2017)
7
Experiments of time-resolved x-ray magnetic circular dichroism (Tr-XMCD) and resonant x-ray scattering
1
at a beamline BL07LSU in SPring-8 with a time-resolution of under 50 ps are presented. A micro-channel
0
plate is utilized for the Tr-XMCD measurements at nearly normal incidence both in the partial electron and
2
total fluorescence yield (PEY and TFY) modes at the L2,3 absorption edges of the 3d transition-metals in
n
the soft x-rayregion. The ultrafastphoto-induceddemagnetizationwithin 50ps is observedonthe dynamics
a
of a magnetic material of FePt thin film, having a distinct threshold of the photon density. The spectrum
J
in the PEY mode is less-distorted both at the L edges compared with that in the TFY mode and has the
0 2,3
potential to apply the sum rule analysis for XMCD spectra in pump-probed experiments.
1
]
t Controlofelectron,magnetic,andlatticestatesbyop- XMCD atthe L absorptionoftransition-metalsis a
e 2,3
d tical excitations in magnetically ordered materials has powerful tool to evaluate the magnetic moments at the
- attracted considerable attention due to their potential specific sites.22,23 Sum rules for XMCD in x-ray absorp-
s
applications in electronic and magnetic recording media tionspectroscopy(XAS)allowustodeterminetheorbital
n
i functioning on an ultrafast time scale below nanosec- andspincontributionstothemagneticmomentsfromthe
s. ond (ns, 10−9 second, GHz range), since the observa- integrated XMCD. The static soft XAS and XMCD in
c tion of the ultrafast demagnetization in Ni within 1 the total electron yield (TEY) mode are the most func-
i
s picosecond (ps), which was explored by time-resolved tional and simple methods, in which the photo-current
y magneto-opticalKerreffect(MOKE)studies.1Theultra- induced by x-ray absorption is measured. In the pump-
h
fast photo-induced changes of magnetic states are non- probe experiments, however, the photo-current induced
p
equilibrium phenomena and several mechanisms have bythepumplaserexceedsthatbytheprobexray. Thus,
[
been proposedto understand them.2,3 These mechanism previouspump-probeXASandXMCDexperimentscon-
1 requirecooperativeeffects,inevitably havingathreshold ducedinALS,LCLS,andBESSYIIhavebeenperformed
v
of the photon density. in the transmissionsetting for thin films on transmissive
6
To capture their non-equilibrium dynamics, ultrafast substrates or foils like Si N , Al and so forth.5,6,8,14,16,17
5 3 4
1 time-resolved experiments have been carried out using However,thegoodqualitiesofmagneticmaterialssuchas
3 ultra-short laser pulses.3 Recently, the development of a aperpendicularmagneticFePtthinfilmareunabletobe
0 bunched synchrotronlightsource and x-rayfree electron achieved on the transparent Si N . The x-ray reflectiv-
3 4
. lasers have enabled investigation of the dynamic phe- ityandXMOKEmeasurementshavealsobeenperformed
1
0 nomena with element selectivity by tuning the photon for non-transparent thin films or bulk samples but with
7 energy of the x-ray to the absorption edges of the con- rather grazed settings for their magnetized axis.9,10,18
1 stituentelements.4–12 Especially,time-resolvedsoftx-ray
To measure non-transmissive as-grown samples at
: spectroscopy has many unique characteristics, such as
v nearlynormalincidence,wepresentsnewsettingsforTr-
i element specificity, chemical specificity and surface sen- XAS and Tr-XMCD in the partial electron yield (PEY)
X
sitivity, which make them versatile for application in a
and total fluorescence yield (TFY) modes. The PEY
r wide range of scientific fields including spintronics and
a mode,inwhichtheemittedphotoelectronsaremeasured,
environmental science. Owing to its importance, var-
israthersurfacesensitivebutthesespectraareknownto
ious time-resolved soft x-ray spectroscopy studies have usuallybesimilartothoseobtainedintheTEY.24Onthe
been carried out.13–21 The time-resolved x-ray magnetic
other hand, the TFY mode, in which the fluorescence of
circular dichroism (Tr-XMCD) and resonant soft x-ray
anx-rayismeasured,isratherbulksensitivecomparedto
scattering (Tr-RSXS) measurements for magnetic and
EY.Despiteitsbulk-sensitivity,therelationshipbetween
electronic materials have been conducted in LCLS,11,12
FY and the absorption coefficient is non-trivial and sat-
ALS,6 and BESSY II slicing facilities.8,9,13–18 The time- uration effects become important in the TFY.25–27 The
resolved x-ray magneto optical Kerr effect (XMOKE)
saturation effects in the TFY often change the ratio of
measurements have also been conducted in FERMI.10
XMCD at the L and L edges and preclude applying
2 3
the sum rule analysis to them.
FePt thin films have drawn intense research interest
a)Electronicmail: [email protected] owingto their potential for highdensity recordingappli-
2
(a) Tr-XAS & Tr-RSXS (b)
TEY TFY(RSXS)
Bunch
chamber fluorescence
photoelectron
RSXS
or scattering
Transfer
Synchrotron rod
Train APD
storage ring sample sample
e-
MCP MCP in V+ MCP inHV-
Soft x-ray anode(HV+) anode(HV+)
or
θ 2θ
Undulator width Sample
~50 ps &magnet Coupled circuit
synchronized 10 deg
with ring’s oscillator MCP Current amp.
Laser Cryo
Ti: sapphire laser ~1 kHz pump
with amplifer 800nm width ~50 fs PEY Oscilloscope
&TFY or Boxcar
1.5 eV Linear
-XAS motion Trigger
FIG.1. (a)OverviewofthesetupforTr-XASandTr-RSXSmeasurementsatBL07LSUofSPring-8. TheTi-sapphirelaserwith
a ∼1 kHzrepetition rate, which is synchronized with the bunches of the synchrotron and delayed electronically, is introduced
into the experimental chamber. The RSXS measurements are preformed at the 0◦ <θ <90◦ side of the chamber (red dashed
box). θ isdefinedastheanglebetweenthex-rayandsamplesurface. TheXASandXMCDmeasurementsinthePEYorTFY
mode are performed at the θ > 90◦ side (blue dashed box). (b) Electrical circuits for the detectors of MCP and APD. The
oscilloscope or Boxcar integrator is triggered by therepetition of thelaser and used for the data accumulation.
cations by using their magnetism.28–33 FePt has a high The scattering is detected by the micro-channel plate
uniaxialmagneticanisotropywhentheL1 orderedstruc- (MCP) or avalanche photodiode (APD) installed on the
0
ture is formed, and exhibits perpendicular magnetiza- 2θ motion of the diffractometer.40 On the other hand,
tion in L1 -FePt (001) thin films, which makes it a can- XAS and XMCD in the PEY or TFY modes are mea-
0
didate for heat-assisted magnetic recording (HAMR),34 sured at the θ >90◦ side of the chamber. Emitted pho-
whichisanalready-workingtechnologythatincorporates toelectrons or x-ray fluorescence are caught by another
laser heating into the recording process. Recently, it MCP topped on the linear motion, which could be posi-
has been shown that proper heat-sink layers optimize tioned as close as ∼2 cm from the sample surface. The
the recording-time window down to 0.2 ns in HAMR of femtosecond Ti:sapphire laser with a wavelength of ∼
FePt.35Thechallengeofachievingshorterrecording-time 800nm housedatthe laser stationofBL07LSU19,20,39 is
has led to an intensive research of the ultrafast magne- introduced into the XAS and RSXS chamber. The laser
tization dynamics. Very recently, Lambert et al. have irradiatessamples10◦belowthex-rayandphoto-induced
showed that circularly polarized laser pulses can induce dynamics of the electronic and structural evolutions are
a small helicity-dependent magnetization in FePtAgC examined by means of the pump-probed technique. The
granular film.36 This finding suggests the possibility of laser pulses with ∼ 1 kHz repetition rate are synchro-
all-optical switching of the magnetism in FePt having nized with selected bunches of the synchrotron and de-
very short recording-time windows on the ps time scale. layed electronically. The spatial and temporal overlap
However, the debate on the origin of this effect is on- between the x-ray and laser beam are monitored using
going, and more experiments are necessary to clarify if the photodiode on the manipulator. The pulse width
FePt could be switched on the ultrafast time scale.37,38 of the Ti:sapphire laser is ∼ 50 fs. On the other hand,
In this letter, the results of Tr-XMCD experiments the single bunch width of the x-rays in the H-mode and
foras-grownFePtfilmswithnon-transmissivesubstrates F-modeatSPring-842 is∼50ps,whichlimits the exper-
are reported. By virtue of the pump-probe technique, a imental time-resolution. Figure 2 shows an example of
photo-induced ultrafast demagnetization at the Fe sites the time-profile of the signals in the F-mode. The sig-
of the FePt thin film having a clear threshold of the nals of the MCP or APD are amplified and gated on the
photon density is clarified within the experimental time- oscilloscope or Boxcar integrator which is triggered by
resolution of 50 ps for Tr-XMCD at SPring-8. the laser pulses [See Fig.1 (b)].
Figure 1 shows an overview of the experimental setup A chevron-type (dual-plate) MCP41 is leveraged for
for Tr-XAS, Tr-XMCD, and Tr-RSXS measurements in XAS and XMCD measurements in the PEY and TFY
thesoftx-rayregionatBL07LSUofSPring-8.39Tr-RSXS modes. Each surface channel of the MCP detects both
◦
is performed at the θ < 90 side of the experimental chargedparticles(photoelectrons)andenergeticphotons
chamber. θ is the angle between the x-ray and sample- (x-ray)andamplifiesthemastheelectriccurrents. When
surface as the standard definition of x-ray diffraction. a positive voltage is applied to MCP-in terminal of the
3
0.15 (a) 707eV 0.02 (b)
interval F-mode 0.00
342.1 ns 0.10 TEY
1/14-filling + 12 bunches 720.2eV µ- -0.02
t8r0a.i8n mA b1u.6n cmhA 00..0050 L3 L2 µ+ --00..0064 Tµ+E Y- µ-
Voltage train pumped bunchtrain Intensity (arb. units)0000....11005050 PEY µµ-+ Intensity (arb. units)---00000.....0000002642 PµE+ Y- µ-
0.02
0.15
0.00
0.10 TFY
µ- -0.02
-4 -2 0 2 0.05 µ+ -0.04 TFY
Time (µs) µ+ - µ-
-0.06
0.00
700 710 720 730 700 710 720 730
FIG.2. Anexampleofsignaloutputobservedontheoscillo- Energy (eV) Energy (eV)
scope during the time-resolved measurements in the F-mode
at SPring-8. The example corresponds to the data at t=30 FIG.3. StaticXMCDspectraoftheFePtthinfilmtakenin
ps taken with the µ− polarization, shown in Fig.4 (a). The the TEY (top), PEY (middle), and TFY (bottom) modes at
dashed box denotes the gated region. Inset shows the bunch room temperature. (a) XASspectra takenat theµ+ and µ−
configuration of theF-mode.42 polarization. Thespectraarenormalizedbytheareabetween
700 and 740 eV. The arrows denote the energies used in the
time-resolved measurements for the L2,3 edges. (b) XMCD
intensities.
surface plate, both the photoelectrons and x-ray fluores-
cence are detected, as illustrated in Fig. 1(b). However,
since the current induced by the photoelectron is much Usingthesumrules,themagneticmomentsattheFesite
larger than that by x-ray, the spectrum can be regarded areestimatedtobemspin=2.63µB andmorbital =0.10µB
to arise from the PEY. Alternatively, when a negative for TEY, and mspin=2.74µB and morbital = 0.15µB for
high voltage (HV) is applied to the MCP-in, the photo- PEY, respectively. Here, the number of the 3d electrons
electrons are bounded and only the fluorescence reaches was assumed to be n3d=6.6. These values are basically
to MCP. In this case, the TFY spectrum is obtained. consistentwithpreviousstudies,43–48whileithasalready
A FePt (001) thin film with the thickness of 50 nm been argued that there were some systematic discrepan-
was epitaxially grown at 500◦C on an MgO (100) sin- ciesarisingfromtheerrorsinthebackgroundsubtraction
gle crystal substrate in an ultrahigh vacuum magnetron procedures.48 Onthe otherhand,the magneticmoments
sputtering system.31 The high temperature deposition areestimatedtobemspin=1.53µB andmorbital =0.08µB
process promoted the L1 ordering of FePt, resulting in fortheTFYspectra,whichexhibitedalargediscrepancy
0
the perpendicular magnetization. Right and left circu- arising from their strong distortion.
larly polarized high-brilliant x-rays (µ+ and µ−) for the Thephoto-induceddynamicsoftheFePtthinfilmwere
XMCD measurement were obtained by combinations of examined in the less-distorted PEY mode. The time-
vertical figure-8 and horizontal figure-∞ undulators in evolutions of the FePt thin film with 16 mJ/cm2 laser
BL07LSU.39 The x-ray beams were focused using a mir- irradiation are given in Fig. 4 (a) at hν=707.0 eV (L3
roranditssizewas100µm×200µmonthesample. The edge) and (b) at 720.2 eV (L2 edge), respectively. As
magnetic field was applied by a 260mT permanent mag- can be seen, almost similar time-evolutions are observed
net placed behind the substrate. XMCD was measured for the Fe L2,3 edges. XMCD, namely the difference of
at 10 degrees off normalincidence (θ = 100◦). The laser theintensitiesatµ+ andµ−,decreasesimmediatelyafter
was linearly polarized and focused to a size φ ∼ 1mm2 the pumped pulse irradiation both at the Fe L2,3 edges.
on the sample. XMCD exhibited a reduction in ts intensity by ∼90% of
theoriginalvalueatboththeL edges∼30psafterthe
Figure3showsthestaticXMCDspectraattheFeL 2,3
2,3 pump pulse. Then the XMCD exhibits a slow recovery
edges forthe FePt thin filmin the TEY,PEY,andTFY
of the magnetization but is not recoveredto the original
modes. Intense XMCD was observed both at the L
edges,∼-40%at707eVand∼6%at720.2eVfortheori2g,3- value even at t=1500 ps, which is completed before the
− next bunch arrives after ∼342 ns. The time-evolutions
inal µ XASinTEYandPEY.Aspectraldifferencebe-
are fitted by the following function
tween the TEY and PEYmode is barely observable. On
the otherhand,XMCD atthe L2 edgeinthe TFYmode I(t)=I1exp(−t/τfast)+I2[1−exp(−t/τrelax)], (1)
isscarcelyobservedowingtothedistortioncausedbythe
saturation effect, although TFY has a bulk-sensitivity. convoluted with the Gaussian response function of the
4
0.15
hv=707 eV (L )
its) 0.14 (a) s) 3
rb. un hv = 707 eV (L3) b. unit 0.14 µ-
ity (a 0.12 16 mJ/cm2 µ- y (ar 0.13
s t
n + si
e µ n 0.12
Int 0.10 nte µ+
I
0.11
0.060
) 0 2 4 6 8 10 12 14 16
s
t 2
ni (b) Laser fluence (mJ/cm )
u
b. 0.055 hv = 720.2 eV (L )
r 2 FIG. 5. Laser-fluence dependence of Tr-XMCD intensities
a
y ( 16 mJ/cm2 µ+ (µ+ and µ−) at t=30 ps on the L3 edge (hν=707.0 eV) for
t the FePt thin film at room temperature. The dashed lines
nsi µ- denoteresultsofthelinearfittingshavingathreshold. Shades
te 0.050 indicate theerror of thefittings.
n
I
for applying a sum rule analysis to XMCD spectra in
0 400 800
theultrafastpump-probedspectroscopyforvariousmag-
Delay Time (ps)
netic materials, which would be very useful to explore
the all-optical switching in spintronics devices such as
FIG. 4. Time-evolutions of XMCD taken in the PEY mode FePt, Co/Pt multi-layers and so forth. On the other
at(a)L3 (hν=707.0eV)and(b)L2 (hν=720.2eV)edgesfor hand, the bulk sensitive TFY method will allow us to
the FePt thin film at room temperature. The power density measure the dynamics of bulk samples showing various
of the laser is 16 mJ/cm2. The solid lines denote the fitting quantumphenomenaincludinghigh-T superconductors,
c
results (see text).
heavy fermion metals and sof forth.
Inconclusion,wehavestudiedthephoto-inducedmag-
netic dynamics of the FePt thin films at the Fe site us-
time-resolution (τ =50 ps). The 4 time-evolutions
Gauss ing the Tr-XMCD technique at nearly normal incidence.
can be fitted with similar time constants of τ =25±
fast The ultrafast photo-induced demagnetization within 50
10 ps and τ = 150±10 ps (solid lines in Fig. 4).
relax ps, which is limited by the width of the bunches from
On analysis, the photo-induced demagnetization occurs
thesynchrotron,isclarifiedwithadistinctthreshold-like
withintheexperimentaltimeresolution<50psafterthe
behaviourMCPhasbeenusedforTr-XMCDbothinthe
pumppulse, andis relaxedwithatime constantof∼150
electron and fluorescence yield modes at the L edges
ps. Itshouldbenotedthatthetimeconstantof∼150ps 2,3
of the 3d transition-metals in the soft-x-ray region. The
for the demagnetizationrecoveryin the FePt thin film is
spectruminthePEYmodeislessdistortedandbasically
muchslowerthanthatobservedintheelementarymetals
similartothatobtainedintheTEYmode. Nodifference
Fe, Ni, and so forth of ∼10 ps,3 and similar to the slow
ofthechangeratioisobservedbetweentheFeL andL
2 3
recovery of several-hundreds ps time scale observed for
edges in the time-resolved measurement, taking advan-
the intermetallic GdFeCo3,14 and Co/Pt multi layers,49
tage of the PEY method.
which also show magnetization reversals induced by the
We acknowledge kind supports provided by Dr. T.
laser pulses.
Ohkochi and Prof. T. Kinoshita. Time-resolved XMCD
Figure5givestheTr-XMCDintensities(µ+andµ−)at
measurements wereperformed with the approvalofSyn-
t=30psasafunctionofthelaserfluence. Thethreshold-
chrotron Radiation Research Organization, the Univer-
like behaviour is observed around 6.5±0.7mJ/cm2 de-
sity of Tokyo (Proposal No. 2016A7504, 2016A7403,
noted by the crossing point of the dashed lines, indicat-
2016B7403, 2016B7518). This research was supported
ing that this effect is a photo-induced cooperative phe-
bytheJapanSocietythePromotionofScience(JSPS)of
nomenon and not a simple thermal effect.2,5,18
Grant-in-Aidfor Scientific Research. This workwas also
Here, we report the advantage of Tr-XAS and XMCD partially supported by the Ministry of Education, Cul-
in the PEY and TFY modes at nearly normal incidence ture, Sports, Science and Technology of Japan (X-ray
for non-transmissive thin films or bulk samples. The Free Electron Laser Priority Strategy Program).
less-distorted PEY method will provide an opportunity
5
1E.Beaurepaire,J.-C.Merle,A.Daunois,andJ.-Y.Bigot,Phys. 22C.T.Chen, F. Sette, Y.Ma, andS.Modesti, Phys. Rev. B42,
Rev.Lett.76,4250(1996). 7262(1990).
2PhotoinducedPhaseTransitions,editedbyK.Nasu,(WorldSci- 23B.T.Thole,P.Carra,F.Sette,andG.vanderLaan,Phys.Rev.
entific,Singapore,2004). Lett.68,1943(1992).
3A. Kirilyuk, A. V. Kimel, and T. Rasing, Rev. Mod. Phys. 82, 24J. T. Lau, A. Fo¨hlisch, R. Nietuby´c, M. Reif, and W. Wurth,
2731(2010)andreferencetherein. Phys.Rev.Lett.89,057201(2002).
4M.Saes,C.Bressler,R.Abela,D.Grolimund,S.L.Johnson,P. 25L.Tr¨oger,D.Arvanitis,K.Baberschke,H.Michaelis,U.Grimm,
A.Heimann,andM.Chergui,Phys.Rev.Lett.90,047403(2003). andE.Zschech, Phys.Rev.B46,3283(1992).
5A. Cavalleri, M. Rini, H. H. W. Chong, S. Fourmaux, T. E. 26A.J.Achkar,T.Z.Regier,H.Wadati,Y.-J.Kim,H.Zhang,and
Glover, P. A. Heimann, J. C. Kieffer, and R. W. Schoenlein, D.G.Hawthorn,Phys.Rev.B83,081106(R) (2011).
Phys.Rev.Lett. 95,067405(2005). 27H. Wadati, A. J. Achkar, D. G. Hawthorn, T. Z. Regier, M. P.
6C. Stamm, T. Kachel, N. Pontius, R. Mitzner, T. Quast, K. Singh, K. D. Truong, P. Fournier, G. Chen, T. Mizokawa, and
Holldack, S. Khan, C. Lupulescu, E. F. Aziz, M. Wietstruk, H. G.A.Sawatzky, Appl.Phys.Lett. 100,193906(2012).
A.Du¨rr,andW.Eberhardt,Nat.Mater.6,740-743(2007). 28C.L.Platt,K.W.Wierman,E.B.Svedberg,R.vandeVeerdonk,
7T. Sato, S. Nozawa, K. Ichiyanagi, A. Tomita, M. Chollet, H. J.K.Howard,A.G.Roy,andD.E.Laughlin,J.Appl.Phys.92,
Ichikawa, H.Fujii, S. Adachi, and S. Koshihara, J. Synchrotron 6104(2002).
Rad.16,110-115(2009). 29T. Shima, K. Takanashi, Y. K. Takahashi, and K. Hono, Appl.
8C. Boeglin, E. Beaurepaire, V. Halt´e, V. L´opez-Flores, C. Phys.Lett. 81,1050(2002).
Stamm, N. Pontius, H. A. Du¨rr, and J.-Y. Bigot, Nature 465, 30C.Moutafis,S.Komineas,C.A.F.Vaz,J.A.C.Bland,T.Shima,
458-461(2010). T.Seki,andK.Takanashi,Phys.Rev.B76104426 (2007).
9K.Holldack,J.Bahrdt,A.Balzer,U.Bovensiepen,M.Brzhezin- 31T. Seki, H. Iwama, T. Shima, and K. Takanashi, J. Phys. D:
skaya, A. Erko A, A. Eschenlohr, R. Follath, A. Firsov, W. Appl.Phys.44,335001(2011).
Frentrup, L. Le Guyader, T. Kachel, P. Kuske, R. Mitzner, 32S. Bedanta, T. Seki, H. Iwama, T. Shima, and K. Takanashi,
R. Mu¨ller, N. Pontius, T. Quast, I. Radu, J.-S. Schmidt, C. Appl.Phys.Lett. 107,152410(2015).
Schu¨ßler-Langeheine, M. Sperling, C. Stamm, C. Trabant, and 33H.Iwama,M.Doi,andT.Shima,Jpn.J.ofAppl.Phys.55,7S3
A.Fo¨hlisch,J.SynchrotronRad.21,1090(2014). (2016).
10Sh. Yamamoto, M. Taguchi, T. Someya, Y. Kubota, S. Ito, H. 34D.Weller,A.Moser, L.Folks,M.E.Best, W.Lee, M.F. Tony,
Wadati,M.Fujisawa,F.Capotondi,E.Pedersoli,M.Manfredda, M. Schwickert, J. U. Thiele, and M. F. Doerner, IEEE Trans.
L. Raimondi, M. Kiskinova, J. Fujii, P. Moras, T. Tsuyama, T. Magn.36,10(2000).
Nakamura, T. Kato, T. Higashide, S. Iwata, S. Yamamoto, S. 35D. Weller, O. Mosendz, H. J. Richter, G. Parker, S. Pisana, T.
Shin,andI.Matsuda,Rev.Sci.Instr.86,083901(2015). S. Santos, J. Reiner, O. Hellwig, B. Stipe, and B. Terris, Sub-
11D. J. Higley, K. Hirsch, G. L. Dakovski, E. Jal, E. Yuan, T. nanosecond heat assisted magnetic recording of FePt media, in
Liu, A. A. Lutman, J. P. MacArthur, E. Arenholz, Z. Chen, G. UltrafastMagnetismI(Springer,NewYork,2015).
Coslovich,P.Denes,P.W.Granitzka,P.Hart,M.C.Hoffmann, 36C.-H. Lambert, S. Mangin, B. S. D. Ch. S. Varaprasad, Y. K.
J. Joseph, L. Le Guyader, A. Mitra, S. Moeller, H. Ohldag, M. Takahashi, M.Hehn, M.Cinchetti, G. Malinowski,K.Hono, Y.
Seaberg, P. Shafer, J. Sto¨hr, A. Tsukamoto, H.-D.Nuhn, A. H. Fainman, M. Aeschlimann, and E. E. Fullerton, Science 345,
Reid,H.A.Du¨rr,andW.F.Schlotter,Rev.Sci.Instr.87,033110 1337(2014).
(2016). 37P.NievesandO.Chubykalo-Fesenko,Phys.Rev.Appl.5,014006
12C. Bostedt, S. Boutet, D. M. Fritz, Z. Huang, H. Ja Lee, H. (2016).
T. Lemke, A. Robert, W. F. Schlotter, J. J. Turner, and G. J. 38M. Berritta, R. Mondal, K. Carva, and P. M. Oppeneer, Phys.
Williams,Rev.Mod.Phys.88,015007(2016). Rev.Lett. 117,137203(2016).
13K.Holldack,N.Pontius,E.Schierle,T.Kachel,V.Soltwisch,R. 39S. Yamamoto, Y. Senba, T. Tanaka, H. Ohashi, T. Hirono, H.
Mitzner,T.Quast, G.Springholz, andE.Weschke, Appl.Phys. Kimura, M. Fujisawa, J. Miyawaki, A. Harasawa, T. Seike, S.
Lett.97,062502(2010). Takahashi,N.Nariyama,T.Matsushita,M.Takeuchi,T.Ohata,
14I. Radu, K. Vahaplar, C. Stamm, T. Kachel, N. Pontius, H. A. Y.Furukawa,K.Takeshita,S.Goto,Y.Harada,S.Shin,H.Kita-
Du¨rr,T.A.Ostler,J.Barker,R.F.L.Evans,R.W.Chantrell,A. mura,A.Kakizaki,M.Oshima,andI.Matsuda, J.Synchrotron
Tsukamoto, A.Itoh, A.Kirilyuk,Th. Rasing,andA.V. Kimel, Rad.21,352-365(2014).
Nature472,205-208(2011). 40ResultsoftheTr-RSXSmeasurementswillbereportedelsewhere.
15M. Wietstruk, A. Melnikov, C. Stamm, T. Kachel, N. Pontius, 41J.L.Wiza,Nucl.Instr.Methods162,587-601(1979).
M.Sultan,C.Gahl,M.Weinelt,H.A.Du¨rr,andU.Bovensiepen, 42Seehttp://www.spring8.or.jp/en/user/operation status/schedule/bunch mode
Phys.Rev.Lett. 106,127401(2011). for more information about bunch configuration of SPring-8;
16N.Bergeard,V.L´opez-Flores,V.Halt´e,M.Hehn,C.Stamm,N. accessed15thNov.2016.
Pontius,E.Beaurepaire,andC.Boeglin,Nat.Commun.5,3466 43C.J.Sun,G.M.Chow,G.H.Fecher,J.S.Chen,H.-J.Lin,and
(2014). Y.Hwu,Jpn.J.Appl.Phys.45,2539(2006).
17A. Eschenlohr, M. Battiato, P. Maldonado, N. Pontius, T. 44S. Imada, A. Yamasaki, S. Suga, T. Shima, and K. Takanashi,
Kachel, K. Holldack, R. Mitzner, A. Fo¨hlisch, P. M. Oppeneer, App.Phys.Lett.90,132507(2007).
andC.Stamm,Nat.Mat.12,332(2013). 45M. M. Soares, H. C. N. Tolentino, M. De Santis, A. Y. Ramos,
18T.Tsuyama,S.Chakraverty,S.Macke,N.Pontius,C.Schu¨ßler- andJ.C.Cezar,J.Appl.Phys.109,07D725(2011).
Langeheine,H.Y.Hwang,Y.Tokura,andH.Wadati,Phys.Rev. 46C. Antoniak, M. E. Gruner, M. Spasova, A. V. Trunova, F. M.
Lett.116,256402(2016). Ro¨mer,A.Warland,B.Krumme,K.Fauth,S.Sun,P.Entel,M.
19M.Ogawa,S.Yamamoto,Y.Kousa,F.Nakamura,R.Yukawa,A. Farle,andH.Wende, Nat.Commun.2,528(2011).
Fukushima, A. Harasawa, H. Kondoh, Y. Tanaka, A. Kakizaki, 47D.B.Xu,C.J.Sun,J.S.Chen,S.-W.Han,S.M.Heald,R.A.
andI.Matsuda,Rev.Sci.Instrum.83,023109(2012). Rosenberg,andG.M.Chow,J.Appl.Phys.111,07C120(2012).
20S. Yamamoto and I. Matsuda, J. Phys. Soc. Jpn, 82, 021003 48M.M.Soares,A.D.Lamirand,A.Y.Ramos,M.DeSantis,and
(2013). H.C.N.Tolentino,Phys.Rev.B90,214403(2014).
21M.Izquierdo, M.Karolak, C. Trabant, K.Holldack, A. Fhlisch, 49N.Kazantseva, U.Nowak, R.W.Chantrell, J.Hohlfeld,andA.
K. Kummer, D. Prabhakaran, A. T. Boothroyd, M. Spiwek, A. Rebei,Europhys.Lett.81,27004(2008).
Belozerov, A. Poteryaev, A. Lichtenstein, and S. L. Molodtsov,
Phys.Rev.B90,235128(2014).
