Resonant soft x-ray magnetic scattering from the 4f and 3d electrons in DyFe(4)Al(8)

0.31 MB·English

by  T. A. W. Beale

Resonant soft x-ray magnetic scattering from the 4f and 3d electrons in DyFe Al
4 8
T. A. W. Beale,1 S. B. Wilkins,2 P. D. Hatton,1,∗ P. Abbamonte,3 S. Stanescu,4 and J. A. Paix˜ao5
1Department of Physics, University of Durham, Rochester Building, South Road, Durham, DH1 3LE, UK
2Brookhaven National Laboratory, Condensed Matter Physics & Materials Science Department, Upton, NY, 11973-5000, USA
3Frederick Seitz Materials Research Laboratory, Department of Physics,
University of Illinois, 1110 West Green St., Urbana, IL 61801-3080, USA
4European Synchrotron Radiation Facility, Boˆıte Postal 220, F-38043 Grenoble Cedex, France†
7 5Departamento de F´ısica, University of Coimbra, P-3000 Coimbra, Portugal
0 (Dated: February 6, 2008)
0
2 Soft x-ray resonant scattering has been used toexamine the charge and magnetic interactions in
the cycloidal antiferromagnetic compound DyFe4Al8. By tuning to the Dy M4 and M5 absorption
n
edgesandtheFeL2 andL3 absorptionedgeswecandirectlyobservethebehavioroftheDy4f and
a
Fe 3d electron shells. Magnetic satellites surrounding the (110) Bragg peak were observed below
J
60 K. The diffraction peaks display a complex spectra at the Dy M5 edge, indicative of a split 4f
2
electron band. This is in contrast to a simple resonance observed at the Fe L3 absorption edge,

which probes the Fe 3d electron shell. Temperature dependant measurements detail the ordering
]
l of the magnetic moments on both the iron and the dysprosium antiferromagnetic cycloids. The
e
ratio between theintensities of theDyM4 and M5 remained constant throughout thetemperature
-
r range, in contrast to a previous study conducted at the Dy L2,3 edges. Our results demonstrate
t the ability of soft x-ray diffraction to separate the individual magnetic components in complicated
s
. multi-element magnetic structures.
t
a
m PACSnumbers: 61.10-i,71.20.Eh,75.25.+z,75.47.Np
-
d
n I. INTRODUCTION length, modulation superimposed resulting in a cyclic
o rotation of the moments in the ab plane with a period
c of approximately 15 unit cells. At a lower temperature
[ The combinationof both a rareearth anda transition
the dysprosiumordersinto the same form, and the same

metal within a single compound raises interesting possi-
1 wavevector,only the cyclic rotationis counter-rotational
bilities for studying their magnetic interactions1,2,3,4,5,6.
v to that of the iron16.
Decipheringtheindividualmagneticcontributionswithin
4
3 these compounds is essential to obtain an overall under- Paix˜ao et al.16 using single crystal neutron diffraction
0 standing of the bulk properties of the sample. The se- and Langridge et al.17 using resonant x-ray diffraction
1 ries of compounds RFe Al where R is a rare earth or found weak superlattice peaks in the [110] directions
4 8
0 actinide element show unusual magnetic properties7,8,9. around Bragg peaks, with a modulation of nτ; where
7 The highly symmetric structure and the relatively weak τ ≈ 0.133 and n is odd. These superlattice peaks arise
0
interactionbetweenthetwomagneticlatticesinthecom- fromthe long-rangecycloidalantiferromagneticordering
t/ pound provides an ideal platform for studying the inter- of the iron and the dysprosium atoms. Paix˜ao et al.16
a
m playbetweenthemagneticions. Thecombinedcontribu- found the value of τ to vary with temperature. Initially
tion from both the iron and the rare earth atoms to the on cooling τ = 0.138 at TN(Fe), and then reducing to
d- overall magnetic structure of DyFe4Al8 has stimulated τ =0.127at∼80K,beforeincreasingagaintoτ =0.132
n considerable interest10,11,12,13. In addition, compounds at 2 K.
o with a higher iron content, such as SmFe Si 14, are fer-
10 2 Neutron studies are extremely sensitive to the mag-
c
romagnets with a high T and have a relatively large
: C netic moments on atoms, however they probe the total
v magnetic anisotropy,factors that are technologicallyim-
magnetic moment, and so it is difficult to determine the
i portant for high field magnets.
X individual elemental contribution of the moments. Al-
r The compound forms a body centred unit cell thoughinthecaseofDyFe4Al8 itwaspossibleusingneu-
a I4/mmm15, with the dysprosium atoms occupying the trondiffractiontoseparatethedysprosiummomentfrom
eightcornersandthecentralposition(Fig.1). Ironatoms the overall magnetic moment through symmetry consid-
occupy a further eight sites forming a cuboids around erations,a direct probe to separatethe elementalcontri-
each dysprosium atom, with the aluminium atoms oc- bution to the total magnetic moment has, until recently
cupying the remaining positions. Detailed studies using notbeenavailable. Resonantx-raystudies,suchasthose
neutron diffraction16 and x-ray magnetic scattering at performedby Langridgeet al., wererestrictedto looking
the Dy L edges17 proposed a complicated magnetic at the 5d band in dysprosium, by tuning to the Dy L
2,3 2,3
structure, where at low temperatures both the dyspro- edges. These edges lie at approximately 8 keV and are
sium and iron magnetic moments are ordered into a cy- easilyaccessibleatresonantscatteringbeamlines. Unfor-
cloidalstructure. BelowT theironordersantiferromag- tunatelythe magneticmomentsonthe atomsinthe title
N
netically in the [110] direction, with a small, long wave- compound occur in the Fe 3d electron band, and the Dy
2
ple face to the beam. Previous neutron16 and x-ray17
scattering experiments on this sample have shown the
existence of superlattice peaks, originating through the
ordering of the iron and dysprosium sublattices. The
sample was examined at the X1B beamline, NSLS, and
the ID08 beamline, ESRF. Both beamlines provide inci-
dentx-rayswithenergiesintheregionoftheDyM and
4,5
FeL edges. Ateachbeamlinethesamplewasmounted
2,3
in the centre of an in-vacuum diffractometer, and cooled
using a liquid helium coldfinger allowinga base temper-
ature of 18 K at X1B and 20 K at ID08. The APPLE
II undulator x-raysourceon the ID08 beamline supplied
100%polarizedlight, whichforthis experimentwascon-
figuredto give a horizontallinear polarized beam, which
FIG.1: (coloronline)ThecrystalstructureofDyFe4Al8. The wascoupledwithaverticalscatteringgeometry. Bycon-
dysprosium (purple) atoms are at the origin and the cen- trast, the X1B beamline has a 28% vertically polarized
ter of the unit cell in a cage formed by the 8 iron (brown)
beam at 1300 eV, while the scattering geometry was in
atoms. The remaining atomic positions are those of alu-
the horizontal plane.
minium (green).
Extremely strong x-ray scattering was obtained from
the(110)Braggpeak,whichisobservableatallenergies.
The peak intensity was dramatically increased at x-ray
4f band,wherethecorrespondingabsorptionedgesliein
energiesclosetothe Dy M edge. The widthofthe peak
the region of 1 keV, energies which until very recently, 5
correspondsto an x-raypenetrationdepth of the 5000˚A.
have not been exploited using diffraction.
Thisisapproximatelywhatwouldbe expectedfrompre-
New advances in soft x-raydiffraction have allowedus
to reach the L edge of the transition metals18 and the viousresults18,confirmingthattheBraggpeakresolution
M edges of the lanthanides19. We have discovered that is limited through the penetration length rather than by
sample quality.
the resonantenhancementof the magnetic x-rayscatter-
ing is considerably larger at these edges, and in addi- Multiple satellites were found in the [110] direction
tion these virtual transitions directly probe the electron aroundthe(110)Braggpeak(Fig.2)withanincidentx-
bands of interest. By tuning to different atomic absorp- rayenergy correspondingto the the M5 edge. The scans
tion edges resonant x-ray scattering is thus an atomic in reciprocal space in the [110] direction correspond to
selective, band sensitive,spectroscopic probe of the elec- the high resolution θ −2θ direction. By comparison to
tronic and magnetic structure. For the first time we the Bragg peak the correlation length of the magnetic
demonstrate that we can directly use resonant soft x- superlatticepeakswas∼250˚A,describingasignificantly
ray scattering at the individual atomic absorption edges less correlated sublattice.
to separate the individual magnetic ordering of the Dy In addition to peaks appearing at (1±nτ,1±nτ,0),
4f and Fe 3d electron bands. where n is odd, corresponding to those observedby neu-
Dramatic changes were found in the integrated inten- tron scattering, we observedpeaks where n was even. A
sityoftheresonant(dipole)featuresattheDyL andL highresolutionenergyscanatfixedQofthe(1,1,0)Bragg
3 2
edgesbyLangridgeet al.17. Thismeantthatthebranch- peakwasmeasured(Fig.3a),andanenergyscanwasalso
ingratio(heredefinedastheratiooftheintegratedinten- collected at the (1−τ,1−τ,0) satellite peak (Fig. 3b).
sities of the L3 to L2 edges) displayed a highly unusual These energy scans covered the vicinity of the Dy M4,5
temperature variation. As we will demonstrate, our ex- edges, and were collected on the ID08 beamline at 20 K,
perimentswhichdirectlyprobetheDy 4f electronband, with∆E ≈50meVat1300eV.Theenergyscansshowa
show no such temperature variation in the 4f electron strong resonance at the Dy M5 edge and a much weaker
band, supporting the theory that the effect observed by resonanceatthe M4 edge. The resonanceofthe satellite
Langridgeet al. occursonlyinthe5delectronband,and peak at the Dy M5 edge was split into two strong peaks
appearsentirelyunconnectedtothemagneticstateofthe at1293eVand1296eV,with a shoulderonthe highen-
system. ergyside of the latter. The Braggpeak showeda similar
resonance,butwithaweakerresonantenhancement,and
a much broader resonance. Proportionally however, the
II. EXPERIMENTAL DETAILS AND RESULTS M edge is stronger, when comparedto the M edge, on
4 5
the Bragg peak than the magnetic satellite peak.
Experiments were performed on a single crystal of A high resolutionenergy scanat fixed Q was takenon
DyFe Al , grownby the Czochralskimethod from a lev- the (1−2τ,1−2τ,0) peak (Fig. 3(c)). This spectrum is
4 8
itated melt using high purity starting materials. The significantlydifferenttospectraofeitherthe Braggpeak
sample was aligned with the [110] direction surface nor- of the magetic (1−τ,1−τ,0) peak.
mal, presenting a highly polished 1 mm × 1 mm sam- The resonantx-ray scattering crossectioncan be writ-
3
(1,1,0) 1
1e+08 (110) Bragg peak
0.8
1e+07
0.6
]
1
-s1e+06 0.4
[
s
Count1e+05 (1-2τ,1−2τ,(01)-τ,1−τ,0) (1+τ,1+τ,0) 0.2
10000 (1-3τ,1−3τ,0) (1+2τ,1+2τ,0) 01
(4τ,4τ,0) nits] 0.8 (1-τ,1-τ,0)
1000 (5τ,5τ,0) b. u
r 0.6
a
0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 [
hk0 [r.l.u.] sity 0.4
n
FIG. 2: Superlattice peaks measured at the Dy M5 edge in nte 0.2
I
the[110]directionfromtheorigin at20K.Datameasuredat
0
X1B. 1
(1-2τ,1-2τ,0)
0.8
ten in terms of geometrical factors depending on the in-
0.6
cident and scattered photons and a tensor characteris-
tic of the scattering ion. For dipole-dipole (E1) transi- 0.4
tions there are three terms and the scattering amplitude
0.2
is given as:
0
1300
fE1 =(ǫ~′·~ǫ)F0+[(ǫ~′×~ǫ)·zˆ]F1+[ǫ~′·T˜·~ǫ]F2, (1) FIG. 3: Scattered x-ray intensity as a function of incident
photon energy at the constant wavevector of (a) Q~ = (110)
where ~ǫ (ǫ~′) are the incident (scattered) x-ray’s polar- (b)Q~ =(1−τ,1−τ,0)and(c)Q~ =(1−2τ,1−2τ,0)through
ization vector and the terms F0, F1 and F2 govern the theDy M4 and M5 edges. Data measured at 20 K ID08.
strength of the resonance and are given by the atomic
properties20.
The first term is a scalar and represents the resonant The temperature dependencies of the (1−τ,1−τ,0)
enhancement of the Thompson charge scattering and is and (1−2τ,1−2τ,0) superlattice peaks at the Dy M
4,5
responsibleforthe enhancementseenonthe(110)Bragg edgesweremeasuredattheX1Bbeamline(Fig.4). Both
reflection. This term does not result in any rotation of superlattice peaks display similar temperature depen-
the photon’s polarization. dences when measured at the M edge, and the signal
5
The second term probes a tensor of rank 1 (vector) of couldbedetecteduptoatemperatureof65K(Fig.4(b)).
odd time reversalsymmetry, and results from a net spin Thistemperaturewasslightlygreaterthanthatdetected
polarizationofthe4f states,adifferencebetweenoverlap through other methods, suggesting soft x-ray diffraction
integrals or lifetime for the two channels21,22,23. This is very sensitive to the dysprosium magnetic moments.
termresultsinarotationofthephoton’spolarization. It The peaks displayed an exponential decrease in inten-
isthistermwhichisresponsibleforthemagneticsatellite sity with increasing temperature through the tempera-
reflections corresponding to (τ,τ,0). turerange17-65K.Measurementswerealsotakenatthe
Thethirdtermprobesatensorofrank2andisevenin DyM edge,wherethesignalfromthe(1−τ,1−τ,0)peak
4
time reversal symmetry. This tensor is invarient under wasundetectable above30K,whilethe(1−2τ,1−2τ,0)
the point group symmetry of the unit cell. This term peak was observed up to 45 K.
is taken to be proportional to the electric quadrupole It has frequently been suggested26 that the iron mo-
moment;i.e. theasphericityoftheatomicchargedensity. ments in these systems orders at ∼180 K. In order to
The asphericitymay be intrinsicto the lattice (asitis in investigate this we experimented with an incident x-ray
the case of Templeton scattering24) or it can be due to energy correspondingto the Fe L edges. This reduced
2,3
the ordering of electric quadrupole moments. It is this the size of the Ewaldsphere,and as such is was not pos-
term which is responsible for the second order satellites sible to reach much further out in reciprocal space than
observed at (2τ,2τ,0). These satellites have previously the (1−3τ,1−3τ,0) superlattice peak. A signal from
been observed in rare earth systems25 and due to their the (1 −3τ,1−3τ,0) magnetic peak was seen only at
appearanceat2Q~ positionsarenormallyonlyobservable the Fe L and L edges (Fig. 5), but no signal was ob-
2 3
in non-colinear super-structures. This term may rotate served at the Fe L edge. We could not observe a signal
1
the polarization of the photon. fromthethe(5τ,5τ,0)peak. Theresonantspectraofthe
4
900
(a) M edge
u.] 0.9 5 L3
r.l. A]
or [0.85 0 m800
Wavevect0.07.58 -1y [s at 25700
b.] 1 (b) M5 edge1 Intensit600 L2
ity [ar 00..68 nsity [arb] 0.1 507000 705 710 715 720 725 730
ns nte0.01 Energy [eV]
e 0.4 I
t
n
I 10 20 30 40 50 60 70 FIG. 5: Scattered x-ray intensity as a function of incident
d 0.2 Temperature [K] photon energy at the constant wavevector Q~ = (1−3τ,1−
e
at 0 3τ,0), measured through the Fe L2,3 edges. No signal was
r
g 1 (c) M edge observedattheFeL1 edge. Thescanwasconductedat17K
te 4 (1-τ,1−τ,0) at X1B.
In 0.8 (1-2τ,1−2τ,0)
d
e 0.6
s
li inFigure6(b). Theintensityofthe(1−3τ,1−3τ,0)peak
m 0.4 was much weaker, even at very low temperatures, than
r
o
N 0.2 the intensity ofthe superlattice peaks atthe dysprosium
absorption edges. As such, although we were only able
0 to detect the (1−3τ,1−3τ,0) peak as high as 55 K, it
100 (d) doesnotnecessarilyfollowthattheordertemperatureof
the iron is lower than that of the dysprosium. However,
M4 75 if indeed the ordering of the iron magnetic lattice is as
/ high as 100 K, then these results show that the ordering
M5 50 of the dysprosium has a large effect on the ordering of
the iron.
25
An alternative explanation for the presence of the
0 (1−2τ,1−2τ,0) superlattice peaks, is that they orig-
10 20 30 40 50 60 70
inate from electron density distortions. Such peaks, also
Temperature [K]
observed by Langridge et al.17, could originate, as sug-
gested by Langridge et al from a magnetoelastic distor-
FIG. 4: (color online) The (a) position and (b) integrated
tion. If such a crystal lattice distortion existed, this sig-
intensity of the (1−τ,1−τ,0) and (1−2τ,1−2τ,0) su-
nal would be present through scattering with photons
perlattice peaks measured at the Dy M5 edge as a function
at non-resonant energies. To test this hypothesis, the
of temperature. The inset of (b) shows the same plot on a
samplewasmountedonthehighenergyx-raydiffraction
logarithmic scale. This clarifies the existence of a signal up
beamline BW5 at HASYLAB, to observe possible weak
to 65 K. (c) The temperature dependence of the integrated
intensity (1−τ,1−τ,0) and (1−2τ,1−2τ,0) superlattice charge superlattice reflecions. High energy diffraction
peaks as measured at the Dy M4 edge. Panel (d) shows the is extremely sensitive to small structural distortions, al-
ratio of the integrated intensity of the superlattice peaks at thoughitisinsensitivetomagneticdiffraction. Thecrys-
theM5 andM4 edges. Notethattheintegratedintensitiesin tal was aligned and cooled, and despite observingstrong
panels (b) and (c) are normalised. Data measured at X1B. Bragg peaks, no superlattice peaks could be seen. This
null resultsuggeststhat there is no accompanyingstruc-
turaldistortion. This suggeststhatthe (1−2τ,1−2τ,0)
peak orginates purely from an aspherical 4f electron
(1−3τ,1−3τ,0)showsasinglepeakcorrespondingtothe
band, andthat the soft x-rayscatteringsignals aremag-
FeL edge,andaveryweakpeakattheFeL edge. Nei-
3 2 netic in origin.
ther peak displayed any fine structure, when measured
with an energy resolution of approximately 220 meV
(X1B).As with the (1−τ,1−τ,0)and(1−2τ,1−2τ,0)
III. DISCUSSION
at the Dy M edge, no large changes were observed in
5
the wavevector of the superlattice peak throughout the
temperature range (Fig. 6(a)). The temperature depen- The temperature dependancies of the superlattice
dence ofthe (1−3τ,1−3τ,0)superlattice peakis shown peaks at the iron and dysprosium edges show distinctly
5
] responds to the ‘true’ ordering of the rare earth. This
.u.0.601 (a) Fe L3 edge is turn effects the size of the magnetic moment on the
l
r. iron, which is observed to increase simultaneously. This
[
r 0.600 is in contrast to that suggested by Paix˜ao et al16, who
o
t suggested from the relative intensities of the (121) (110)
c
ve0.599 peaks, that there is no increase in the iron moment at
ve0.598 TDy. Resonant soft x-ray diffraction can detect a rela-
Wa tive change in the magnitude of the magnetic moments
on the individual atomic species, however it is unable to
providea quantitativemeasureofthe magneticmoment.
1.0 (b) Fe L edge
3 The earliest powder neutron measurements12 on
ts] 0.8 DyFe4Al8 found only one magnetic transition at 25 K
ni 0.6 which was attributed to ordering of the iron moments
u
into a conical spiral structure. It seems likely, however
.
b 0.4 that this transition is in fact due to the ordering of the
r
a
[ 0.2 dysprosium moments. The suggested ordering tempera-
y
tureforthedysprosiummomentsof30Kissupportedby
t
si 0.0 temperaturedependentmeasurementsoftheACandDC
n
nte 1.0 (c) Dy M5 edge magnetic susceptibilities of DyFe4Al8 by Talik et al.26.
I They found the magnetic susceptibilities to have a pro-
d 0.8 nounced peak at 30 K. In addition a thermomagnetic
e
at 0.6 effect was found below 30 K. Partialorderingof the iron
r
g sub-latticeisbelievedtooccurinthe temperatureregion
e 0.4
nt 50-180 K. Bulk Mo¨ssbauer measurements also suggest
I 0.2 that the iron atoms order at 180 K. It is difficult from
this study to accuratelypin downT as the intensity at
0.0 Fe
10 20 30 40 50 60 the Fe L edge is very low, and there is no sudden drop
3
Temperature [K] in intensity suggesting a sudden transition. However the
behaviour of the signalat the Dy M edge is much more
5
FIG. 6: (color online) Temperature dependence of the (a) conclusive for defining TDy.
wavevectorand(b) intensityofthe(1−3τ,1−3τ,0) peakat Previous resonant x-ray scattering studies had em-
theFeL3edge. TheintegratedintensityattheDyM5edgeas ployed the Dy L and L edges. These probe electronic
2 3
a function of temperature (c) is shown for comparison. Data
dipole transitions (E1) from the 2p (L edge) and the
1/2 2
measured at X1B. The vertical dashed line is placed at TDy, 2p (L edge) core levels to the empty 5d states. Such
thehorizontal dashed line is a guide tothe eye. 3/2 3
techniques are generally only indirectly sensitive to the
4f magnetic ordering. They do however give informa-
tiononthespinpolarisationofthe5dbandwhichiscou-
different behaviour. Firstly it should be noted that the pledtothepartiallyfilled4f shellviaspin-orbitcoupling
signalobservedattheFeL edgewassignificantlyweaker and band structure effects. Coupling between the 4f
3
than that observed at the Dy M edge. The signal at moments is important in stabilising many complex mag-
5
the dysprosium edge was first observed at 65 K (Fig. netic structuresviathe Ruderman-Kittel-Kasuya-Yosida
4), and at the iron edge at 55 K (Fig. 6). This ini- (RKKY)mechanism. Systematic studies by Kimet al.27
tiallysuggeststhatthedysprosiummomentsorderbefore of the resonant scattering amplitudes in RNi2Ge2 (R =
the iron. However upon cooling, at 30 K the signal at Gd, Tb, Dy, Ho,Er,Tm)found thatthe branchingratio
the dysprosium increases substantially, simultaneous to (theratiooftheL3/L2 resonantscattingintensities)var-
arathersmallerincreaseinthe signalattheironabsorp- iedasafunctionoftherareearthelements. InGdNi2Ge2
tion edge. Previous studies have consistently detected a it the ratio was almost unity, then increased to 3.5 in
relatively high ordering temperature of the ironmoment DyNi2Ge2 and then to 8.0 in ErNi2Ge2. Such effects are
(∼ 100−180 K), and a much lower ordering tempera- due to increasing spin-orbit coupling and 4f orbital po-
ture of the dysprosium magnetic moment (∼30 K). Our larisation. In nearly all resonantx-rayscattering studies
resultsthereforesuggestthatthehightemperatureorder- of particular materials this branching ratio is constant
ing of the iron moments induces a small moment on the at all temperatures. This is because the electronic band
dysprosium sites. The relative intensities of the signals polarisation effects are generally insensitive to thermal
observed suggest that the soft energy resonant diffrac- effects.
tion is more sensitive to the dysprosium moment, hence Langridgeet al.17 foundthatinDyFe Al thisbranch-
4 8
the failuretoobservethe ironmomentathighertemper- ing ratio (L /L ) was temperature dependent. Below
3 2
atures. As the sample is cooled further, the significant 20 K the Dy L resonance dramatically increased in
3
increase in the moment on the dysprosium moment cor- intensity whereas the Dy L resonance decreased. In
2
6
all these measurements the resonances were very sim- Fe L edges. These have shown different tempera-
2,3
ple, comprised of a single E1 dipole transition. There ture dependencies suggesting the iron initially orders at
was no sign of an higher multipole orders such as E2 T ≥65K,andthedysprosiumorderingatT ≈30K.
Fe Dy
(electric quadrupole). Langridge et al. speculated that The ordering of the dysprosium appears to be signifi-
the temperature dependence of the branching ratio was cantly stronger, although quantitative comparisons are
caused by changes in the 5d band polarisation caused difficult to make. The superlattice peaks at the Dy M
5
by the increasing ordered component of the Dy 4f mo- edge appear at (1±nτ,1±nτ,0), where n is both odd
ment andsimultaneous magnetoelasticdistortions below and even. It is unclear what the origin of the peaks at
T . Our measurements (Fig. 4(d)) show no change in evenn aredue to. There was no observationofa change
Dy
the branching ratio of the integrated intensity a the M inwavevectorofanyofthesuperlatticepeaksthroughout
5
and M edges). It is clear that even if there are changes the temperature range that they could be observed.
4
in DyFe Al below 30 K in the spin polarisation of the
4 8
5d band, these are not replicated in the 4f band.
It was noted by Paix˜ao et al.16 that the modulation
V. ACKNOWLEDGEMENTS
vector of the magnetic superlattice changes slightly be-
low T . Although no significant change is obvious in
N
our results (Fig 4(a)), there is a slight variation from a TAWB wishes to thank EPSRC for support. PDH
constant value which is compatible with the previously thanks the University of Durham Research Foundation
published results. for support. PDH and TAWB acknowledge travel assis-
tance from EPSRC. The authors would like to acknowl-
edge the European Synchrotron Radiation Facility for
IV. CONCLUSION
provision of synchrotron radiation facilities. X-ray mea-
surementsatX1B,NSLSweresupportedbytheOfficeof
The magnetic structure of DyFe Al has been stud- BasicEnergySciences,U.S.DepartmentofEnergyunder
4 8
ied using resonant soft x-ray diffraction. Superlattice Grant No. DE-FG02-06ER46285, with use of the NSLS
peaks have been observed at the Dy M edges and supported under Contract No. DE-AC02-98CH10886.
4,5
∗ Electronic address: [email protected] (2001).
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