x-ray and neutron science 2016 · 2016-09-23 · x-ray magnetic circular dichroism (xmcd) is...

X-RAY AND NEUTRON SCIENCE 2016

Magnetism and X-ray dichroism

A. Rogalev

A. Rogalev | Magnetism and X-ray Dichroism | 3rd ESRF/ILL International Student Summer Programme | 06. 09. 2016

OUTLINE

A. Rogalev | XMCD | VI Euro-Asian Symposium «Trends in Magnetism» | 15-19 August 2016

Introduction to X-ray Magnetic Circular Dichroism

Experimental aspects: ID12 beamline at the ESRF

Selected Results

Single molecular magnets

Orbital magnetic moment in actinides

Conclusions

1994

Nobel Prize

in PhysicsCliff Shull Bert Brockhouse

Nobel Prize in Physics 1994: B. N. Brockhouse and C. G. Shull

Press release by the Royal Swedish Academy of Sciences:

“Neutrons are small magnets…… (that) can be used to study the relative

orientations of the small atomic magnets. ….. the X-ray method has been

powerless and in this field of application neutron diffraction has since

assumed an entirely dominant position. It is hard to imagine modern

research into magnetism without this aid.”


The Agilent Technologies Europhysics Prize for outstanding achievement

in condensed-matter physics in 2000:

P. Carra, G. Schütz and G. van der Laan

“for their pioneering work in establishing the field of magnetic X-ray

dichroism. …it is possible to obtain information about the material that

cannot be obtained with traditional measurements.”


Nowadays:

X-ray magnetic circular dichroism (XMCD) is considered to be one of the

most important discoveries in the field of magnetism research in the last

two decades. It is hard to imagine modern research into magnetism

without the aid of X-ray spectroscopy.



“Magnetism, as you recall from physics class, is a powerful force that causes certain items to be attracted to refrigerators.”

- Dave Barry

Clean

Energy

APPLICATIONS OF PERMANENT MAGNETS

Rare Earth permanent magnets help

make technologies more effective and

more efficient.

direct-drive wind turbines require ~ 600 kg of permanent magnet material

to produce 1 megawatt of electric power

1118 magnets (inc. 2.9kg of Nd-Fe-B)

2008 Lexus RX Hybrid

High-Efficiency

Motors for Energy-

Efficient Homes

Industry

Magnetic resonance Imaging Computing and

communication

technologies

Aerospace



Spin and orbital magnetic moments are coupledvia spin-orbit interaction, which is the keyingredient in magneto-optics, magnetocrystallineanisotropy, magnetic chirality, etc


The experimental technique capable to measure separately SPIN and ORBITAL moments of an atom is

X-ray Magnetic Circular Dichroism (XMCD)

Difference in absorption cross-section of circularly polarized X-rays for sample magnetization either parallel or antiparallel to the X-ray wavevector

Photon could be• absorbed (photoelectric effect)• elastically scattered• inelastically scattered

92U

below 200 keV absorption dominates

X-RAY INTERACTIONS WITH MATTER

M edges

L edges

K edge

n=1

} n=2

}n=3

} n=4

K

L1

L2

L3

M1

M2,3

M4,5

N1-5

l=0

l=0

l=0

{l=1

{l=1

{l=2

Spin-orbit interaction splits level in 2

A. Rogalev | X-ray dichroisms | JABS10, Bordeaux | 6-7 Juin 2016

X-RAY ABSORPTION SPECTROSCOPY


XANES X-ray Absorption Near Edge Structure

EXAFS

Extended X-ray Absorption Fine Structure

pre-edge

edge

[Fe(viz)4ReF6]

viz = 1-vinylimidazole

X-RAY ABSORPTION SPECTROSCOPY


Fe K-edge

1s → 4p Re L3-edge

2p3/2 → 5d3/2,5/2

Re L2-edge

2p1/2 → 5d3/2

In the early days of XAFS, absorption edges taken with use of photographic plates, appeared as unexposed bands on the plate (developed in negative), or “white lines”

white lines

Element and orbital selectivity of X-ray Spectroscopy

Photon could be• absorbed (photoelectric effect)• elastically scattered• inelastically scattered

92U

M edges

L edges

K edge

n=1

} n=2

}n=3

} n=4

K

L1

L2

L3

M1

M2,3

M4,5

N1-5

l=0

l=0

l=0

{l=1

{l=1

{l=2

Spin-orbit interaction splits level in 2


For magnetism research, the key word - POLARIZATION

X-RAY INTERACTIONS WITH MATTER

REMINDER: LIGHT AS A EM FIELD

𝑨 = 𝑨𝟎𝑒𝑖(𝜔𝑡−𝒌⋅𝒓)

𝒖

𝑬 = −𝑖𝑬𝟎𝑒𝑖(𝜔𝑡−𝒌⋅𝒓) 𝑬𝟎 = 𝜔𝑨𝟎

𝑩 = −𝑖𝑩𝟎𝑒𝑖(𝜔𝑡−𝒌⋅𝒓) 𝑩𝟎 = 𝒌 × 𝑨𝟎

with the wave vector 𝒌 such that 𝑘2 =𝜔2

𝑐2𝒌 =

2𝜋

𝜆𝒖 =

𝜔

𝑐𝒖

when 𝒌 along z: 𝑨𝟎 =𝐴0𝑥𝑒

𝑖𝜑0𝑥

𝐴0𝑦𝑒𝑖𝜑0𝑦

0

:

𝜑0𝑥 = 𝜑0𝑦 linearly polarized light

𝜑0𝑥 − 𝜑0𝑦 = ±90°𝐴0𝑥 = 𝐴0𝑦 circularly polarized light


POLARIZATION OF LIGHT

Polarization vector 𝝐 =𝑬

𝐸0

𝒌 // z

𝝐 =100

𝝐 =1

2

1𝑖0

𝝐 =1

2−1𝑖0

Note: the phase conventions are highly variable


X-RAY MAGNETIC CIRCULAR DICHROISM

The first serious approach to the problemof absorption of circularly polarized X-rays

Two-step model


TWO STEP MODEL OF XMCD

A. Rogalev | X-ray Spectroscopy | 11th SPCA | 14. Mars. 2016

Absorption of a right circularly polarized photonelectric dipolar transitions 𝒑 → 𝒅 (𝚫𝐦𝐥 = +𝟏;𝚫𝐦𝐒 = 𝟎)

Excited photoelectrons are spin polarized

d continuum

|ml,ms>: |2,↑> |1,↑> |0,↑> |0,↓> |1,↓> |2,↓>d continuum

|ml,ms>: |2,↓> |1,↓> |0,↓> |0,↑> |1,↑> |2,↑>

√⅔|1,↓> + √⅓|0,↓> - √⅔|-1,↑> - √⅓|0,↑>

60% 15% 10% 15%

<σz>= -1/2

|1,↑>+√⅔|0,↑>+√⅓|-1,↑>+|-1,↓>+√⅔|0,↓>+√⅓|1,↓>

<σz>= 1/4

7.5% 15% 15%2.5%15%45%

LIII-edge (2p3/2) LII-edge (2p1/2)

TWO STEP MODEL OF XMCD

Exchange splitting of the valence band is driving the second step


FIRST EXPERIMENTAL OBSERVATIONS


First experimental evidence

XMCD is a new approach to study ferromagnetic system

XMCD SUM RULES


Orbital sum rule

Spin sum rule

z

jj

LCccll

ll

)1(2)1(

)1(2)(

Sum rules relate experimental XMCD spectra to the spin and orbital moments

j

zz

j

TBSACc

c][)(

1)(

jjhnC )(

1 0 - X-ray absorption cross section per hole;

c

ccllA

3

)1(2)1(

)1(6

)2()1(3]4)1(2)1()[1(22

llc

cccccllllB

i

iiiii rsrrsT )/)(3( 2

CHARGE SUM RULE


integrated whitelines intensity is measure for number of holes

in the valence band => valence state

F. Wilhelm, et al. Phys. Rev. Lett 85, 413 (2000) A. Rogalev et al. Lect. Notes Phys. 697, 71(2006)

A.F. Starace, Phys. Rev. B5, 1773 (1972)

APPLICATION OF THE XMCD SUM RULES FOR THE L2,3 EDGES


11.52 11.56 11.60 13.24 13.28 13.32

-1.0

-0.5

0.0

0.5

1.0

1.5

Pt

Pt

Au metal

Co12

/Pt12

multilayer

Pt L2

Pt L3

H=6Tesla

T=5K

XA

S In

ten

sit

y (

a.u

.)

Photon Energy (keV)

-0.10

-0.05

0.00

0.05

0.10

0.15

XM

CD

(a.u

.)

(h

Ptn n

h

Au )-C =

A

<L >Z

= - 43

. C .

= -<S >Z <T >Z- 7 2C .

<L >Z

<S >Z <T >Z-7

23

.=

~ integrated intensity of

transitions into unoccupied d band

n = number of holes in d bandh

d

A

in the case of L3,2 absorption edges

(A + B)

(A - 2 B)

(A + B)

(A - 2 B)

integrated spectra related to spin and orbital magnetic moments

in the ground state B.T Thole et al., Phys. Rev. Lett. 68,1943 (1992)

P. Carra et al. Phys. Rev. Lett. 70, 694 (1993).

ELEMENT SELECTIVITY OF XMCD


Ni2 / Pt2 multilayer

T ~ 10K

H = ± 5 T

RESULTS

• Ni magnetic moments:

S3d=0.35 B/atom

L3d=0.038 B/atom

• Pt induced magnetic moments:

S5d=0.14 B/atom

L5d=0.03B/atom

11.55 11.60 13.25 13.300.0

0.5

1.0

1.5 Pt

L2

L3

(+)

(-)No

rm. X

AS

(a.u

.)

Photon Energy (keV)

-0.04

-0.02

0.00

0.02

0.04

XM

CD

(a.u

.)

xmcd

840 860 880 900-4

-2

0

2

4 Ni

(+)

(-)

Photon Energy (eV)

L2

L3

No

rm. X

AS

(a.u

.)

-1.0

-0.5

0.0

0.5

1.0

1.5

XMCD

XM

CD

(a.u

.)

Ni

Ni

Ni

Pt

Pt

Pt

F. Wilhelm et al., Phys. Rev. Lett., 85, 413 (2000)

SENSITIVITY OF XMCD


11880 11900 11920 11940 11960 11980 12000-0.012

-0.010

-0.008

-0.006

-0.004

-0.002

0.000

XM

CD

Photon energy (eV)

11880 11900 11920 11940 11960 11980 120000.0

0.2

0.4

0.6

0.8

1.0

1.2

Norm

aliz

ed

Ab

so

rptio

n

13680 13700 13720 13740 13760 13780 13800 13820 138400.0

0.2

0.4

0.6

13680 13700 13720 13740 13760 13780 13800 13820 13840

0.000

0.002

0.004

0.006

0.008

0.010

0.012

Au LIII-edge Au LII-edge

Au4Mn

Tc ~ 360 K

T = 10 K

H = 3 T

<Sz> = 0.0353(5)B <Lz>=0.0054(5)B (per Au atom)

To compare with 4.15B per Mn atom

SENSITIVITY OF XMCD: A SINGLE SURFACE-ADSORBED ATOM


Ho atoms on a two-monolayer-thick MgO film deposited on Ag(100)

STM Image

F. Donati et al., Science 352, 318-321 (2016)

ESRF ID32Ho = 0.01 ML

T = 6.5 K

INDUCED MAGNETISM ON GOLD ATOMS


Fe

W

Fe

Co12/Au4 multilayer

𝜇𝑡𝑜𝑡𝐴𝑢 ≈ 0.031𝜇𝐵/𝑎𝑡𝑜𝑚

W

Fe




𝑨𝒖𝟑𝑭𝒆𝟗𝟕𝑨𝒖𝟓𝟎𝑭𝒆𝟓𝟎𝑨𝒖𝟕𝟓𝑭𝒆𝟐𝟓


(T = 2.3K; H = 17 T)

OUTLINE




Selected Results



Conclusions

XMCD EXPERIMENT

+, -=> Absorption cross-sections for CP X-rays with

( + ) helicity parallel to the sample magnetization

( - ) helicity antiparallel to the sample magnetization

Quantity to measure: D = + - -

Source of monochromatic circularly polarized X-rays

Magnetic field to magnetize a sample

Highly performing X-ray detectors

The best possible at the 3rd generation synchrotron radiation facilities

A. Rogalev | X-rays and Magnetism | ESRF | 12 November 2015

SOURCE OF CIRCULARLY POLARIZED X-RAYS


BzBx

PHASE

lu

31 periods

lu = 52 mm

bhg

thg

thg = 6.0 mm

(Bz=0.493 T)

bhg = 6.0 mm

(Bx=0.349 T)

Flux: 1014 ph/s/0.1%bwP. Elleaume, J. of Syn. Rad., 1, 19-26 (1994)

Full control of polarization: flipping time ~ 5 seconds

Bx = Bz

-lu/4PHASE 0 lu/4 lu/2

E1min=1.7 keV, E1

max=6.2 keV

ESRF BEAMLINE ID12

X-ray MagneticScattering0<QB<18

o

0.6 T; >20K

High field XMCD 17 T; > 2K

XDMRLow field XMCD0.9 T; >15K

XMCD onnanostructures6T; >1.5 K

XNCD/XNLD

High PressureXMCD 6T, >2.7K

Spot size 1m(V) x 20m(H) with

Be refractive lenses

over whole spectral range 2-15 keV


ESRF BEAMLINE ID12

K - edge

L - edges

M - edges

2.05 keV - 15 keV


HIGH FIELD XMCD END-STATION

H < ± 17 Tesla, T > 2.0 K

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

3.64 3.66 3.68 3.70 3.82 3.84 3.86 3.88 3.90

0

1

2

3

4

5

6

7

8 h<+>

h<->

XA

NE

S (

a.u

.)

Photon Energy (keV)

Np M4

XM

CDNp M

5

5K

17T

NpOs2

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

-15 -10 -5 0 5 10 15

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

XMCD

-XM

CD

Np

M4

Magnetic Field (T)

5K

E=3844,8eV

SQUID

Aldred et al.

Ma

gn

etiz

atio

n (

B /f.u.)

NpOs2

Aldred et al., PRB10, 1011(1974) Wilhelm et al., PRB 88, 024424 (2013)

Typical sample size

0.65mm X 0.80mmx0.12mm


Element-specific and orbital-selective magnetometry tool

Sensitive to the electronic structure (valence state, symmetry,… )

Possibility to extract Spin and Orbital magnetic moments of

absorbing atoms only

Small size samples (focusing the x-ray beam)

Single crystals, polycrystalline and amorphous materials, thin films,

nanoparticles, monolayers, ad-atoms, …

X-ray Magnetic Circular Dichroism is a unique tool to study microscopic magnetic properties


OUTLINE




Selected Results



Conclusions

MAGNETIC STRUCTURES


θ

0 180

energ

y

1020 1010 108 106 105 104 103 102 10 1

permanent

magnets

micro-

particles

nano-

particles clusters

Paramagnets and

Single-molecule

magnets

classical nanoscopic quantum

Z (T) = 0 exp{Δeff /(kBT)}Mn12ac

Low

temperature!

H =DSZ 2

4D/5D IONS IN SINGLE MOLECULAR MAGNETS


4 4 212 3 1

2

1

( )( 1)em Z c

n l l ll

Kim et al. Phys. Rev. Lett. 2008, 101, 076402

Kim et al. Science, 2009, 323, 132

Machida et al. Nature 2010, 463, 210

Modic et al. Nat. Commun. 2014, 5, 4203

Sr2IrO4

…..but also:

A2Ir2O7 (pyrochlores)

A2IrO3 (honeycomb)

A4Ir3O8 (hyperkagome)

Chun et al. Nat. Phys. 2015, 11, 462

Chen et al. Nat. Commun. 2015, 6, 6593

Kim et al. Nat. Phys. DOI: 10.1038/NPHYS3503

Zhao et al. Nat. Phys. DOI: 10.1038/nphys3517

EXOTIC MAGNETIC PHENOMENA IN “IRIDATES”


{IrO6}8–{IrF6}2–

[IrF6]2–

Electronegativity

Mass and size

Redox-innocence

….

GETTING SOME [MF6]X-


[ReCl6]2–

NH4HF2(l)

[ReF6]2–

K. Pedersen et al, Angew. Chem. Int. Ed. 2014, 53, 1351

SOME INDICATIONS OF ORBITAL MAGNETISM


En

erg

y

XMCD OF [IrX6]2- COMPLEXES


[IrF6]2– [IrCl6]

2– Sr2IrO4

Sz 0.13 0.15 0.15

Lz 0.77 0.65 0.63

OUTLINE




Selected Results



Conclusions

THE ANFE2 SYSTEM

Laves phase, C-15 structure, fcc unit cell

TCs between 160 K (UFe2) and ~700 K (AmFe2)

Easy magnetization direction: <111> (U,Np) or <100> (Pu,Am)


X-RAY ABSORPTION SPECTROSCOPY: SPIN-ORBIT SUM RULE


EF

3d3/2

3d5/2

5f7/2

5f5/2

ℏ𝜔

Δ𝑙 = ±1; Δ𝑠 = 0; Δ𝑗 = 0;±1

dipolar transitions

M5-edge M4-edge

M5M4

𝑰𝑴𝟓+ 𝑰𝑴𝟒

∝ 𝒏𝒉𝟓𝒇

𝑩 =𝑰𝑴𝟓

𝑰𝑴𝟓+ 𝑰𝑴𝟒

< 𝒍. 𝒔 >=𝟑

𝟐𝒏𝒉𝟓𝒇

𝑩 −𝟑

𝟓+ 𝚫

M4,5 X-RAY ABSORPTION SPECTRA OF ACTINIDES


Intensity of the M5 XANES spectra decreases from U to Cm

Intensity of the M4 XANES spectra decreases from U to Pu but increases for Cm

-30 0 30 120 150 180 210 240 270

0

2

4

6

8

10

12

14

16

UFe2

NpFe2

PuFe2

AmFe2

Cm metal

Am

Cm

Pu

Np

M4

iso

tro

pic

XA

NE

S (

a.u

.)

E - E0

M5

U

M5

< l.s > = -3/4nh(2IM5-3IM4)/(IM5+IM4) + D

= 3/2 n7/2 – 2 n5/2

Δ = -0.014, -0.010, -0.005, 0.000, +0.005, +0.015

for ne5f =2, 3, 4, 5, 6, 7

G. van der Laan, Phys. Rev. Lett. 93, 097401 (2004)

SPIN-ORBIT SUM RULE:

APPLICATION OF THE SPIN-ORBIT SUM RULE


XANES spectra were measured on

UO2 for ionic state of U close to 5f 2 configuration

U/Fe multilayers, UFe2 for 5f3 configuration

NpFe2 for 5f4 configuration

PuFe2 for 5f5 configuration

AmFe2 for 5f6 configuration

Cm metal for 5f7 configurationUncertainty of a few %

B ne5f 2/3<l.s> n5/2 n7/2

U4+ 0.65 2 -1.67 1.57 0.43

α-U3+ 0.687 3 -2.52 2.37 0.63

Np 0.742 4 -3.6 3.26 0.74

Pu 0.803 5 -4.56 4.10 0.90

Am 0.88 6 -5.56 4.95 1.05

Cm 0.735 7 -2.26 3.97 3.03


LDA+DMFT : J. H. Shim, K. Haule and G. Kotliar, Euro. Phys. Lett. 85, 17007 (2009)

Atomic multiplets: K. T. Moore and G. van der Laan, Rev. Mod. Phys. 81, 235 (2009)

Experiment: EELS and XAS (K.T. Moore and G. van der Laan)

APPLICATION OF THE SPIN-ORBIT SUM RULE

5f states are well described with intermediate coupling scheme

X-RAY ABSORPTION SPECTROSCOPY: SPIN-ORBIT SUM RULE


EF

3d3/2

3d5/2

5f7/2

5f5/2

ℏ𝜔

Δ𝑙 = ±1; Δ𝑠 = 0; Δ𝑗 = 0;±1

dipolar transitions

M5-edge M4-edge

5f spin-orbit splitting

US

single crystal

M4,5 XMCD OF ACTINIDES

-30 0 30 120 150 180 210 240 270

-2

0

2

4

6

8

Am

UFe2

NpFe2

PuFe2

AmFe2

Cm metal

Cm

Pu

Np

M4

XM

CD

(a

.u.)

E - E0

M5

UM5 • XMCD spectral shape at the M5-edge

has an asymmetric S shape for light

actinides (U-Am) but becomes symmetric

for Curium metal

• XMCD spectral shape at the M4-edge has

slight asymmetry on high energy side and

negative for light actinides but changes the

sign for Curium metal.

M4,5 XMCD spectra normalized to unity at M4


M4,5 XMCD OF ACTINIDES


L ( B ) S ( B ) - L / S

X M C D 0 .2 1 0 .0 2 - 0 .2 0 0 .0 2 0 .9 7 0 .0 5

N e u t r o n 0 .2 3 0 .0 1 - 0 .2 2 0 .0 2 1 .0 5 0 .0 5

T h e o r y 0 .4 7 - 0 .5 8 0 .8 1

ferromagnet with Tc = 160 K

Fe = 0.58 B and U ~ 0 B

3540 3560 3700 3720 3740 3760

-20

0

20

40

60

80

100

XMCD * 10

T = 20 K

H = 2 TUFe2

U-MIV,V

edges

Flu

ore

sc

en

ce

In

ten

sit

y (

a.u

.)

Energy (eV)

MAGNETIC DIPOLE TERM


<Tz> is a measure of a spin moment anisotropy

induced either by a charge quadrupole moment or by the spin-orbit interaction

One can estimate <TZ> via combination of XMCD with

Neutron scattering, magnetic Compton scattering or SQUID measurements

There are no any direct measurements of this term (so far !!!)

G. van der Laan, B.T. Thole, Phys. Rev. B 53, 14458 (1996)

XMCD IN AMFE2

Sum rules analysis:

⟨Lz⟩ = - 0.44(5)

⟨Sz⟩ + 3⟨Tz⟩ = - 0.135(15)

⟨Jz⟩ = ⟨Lz⟩ + ⟨Sz⟩ = 0

μL = -⟨Lz⟩ = + 0.44 μB

μS = -2⟨Sz⟩ = - 0.88 μB

3⟨Tz⟩ = - 0.57

Calculated: (with Hint = 180 T)

μL = -⟨Lz⟩ = +0.47 μB

μS = -2⟨Sz⟩ = -0.94 μB

3⟨Tz⟩ = -0.51


MAGNETISM IN UTX TERNARY COMPOUNDS


,Ir2

,Ir1

• UIrAl (μTOT = 0.98 μB) TC=64K

• UPtAl (μTOT = 1.38 μB) TC=43K

Both are ferromagnets

A.V. Andreev, J. Alloys Compd. 336, 77 (2001)

U M4,5 XANES SPECTRA IN UTX CRYSTALS


Isotropic spectra are similar at M5-edge

M4-edge XANES shows that there are more 5f5/2 holes in UIrAl

Different expectation value of the 5f

spin-orbit interaction per hole

U valence state in UIrAl seems to be U4+

whereas in UPtAl it is U3+

Exp. error bars ~%

for ne5f =2

D =-0.014

3.52 3.54 3.56 3.58 3.70 3.72 3.74 3.76 3.78

0

2

4

6

8

U

UPtAl

UIrAl

M5

XA

NE

S (

a.u

.)

Photon Energy (keV)

M4

k //c-axis

B 2<l.s>/(3.nh5f

) - D ne5f

n5/2 n7/2

2 (U4+) 1.62 0.38 UIrAl

0.654 -0.135

3 (U3+) 1.96 1.04

2 (U4+) 2.11 -0.11

UPtAl 0.692 -0.230 3 (U3+

) 2.42 0.58

for ne5f =3

D =-0.010


Strong XMCD at the M4-edge

s-like shape XMCD at the M5-edge

element specific magnetization curves recorded at U similar to the macroscopic one

3.52 3.54 3.56 3.58 3.70 3.72 3.74 3.76 3.78

-8

-6

-4

-2

0

2

4

6

8

XA

NE

S (

a.u

.)

Photon Energy (keV)

-1.2

-0.9

-0.6

-0.3

0.0

0.3

0.6

0.9

1.2

-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0

-1.0

-0.5

0.0

0.5

1.0

T=5K

H//c-axis

U M4-edge

E0=3.726keV

-X

MC

D M

4-e

dg

e

Magnetic Field (Tesla)

U

T=5K

H=3T

U M4

U M5

UIrAlX

MC

D

XMCD at the U M4,5-edges in UIrAl crystal


XMCD at the Ir L2,3-edges in UIrAl crystal

LIr

(5d)

(B /atom)

SIr

(5d)

(B /atom)

totIr

(5d)

(B /atom)

LIr

(5d)/ SIr

(5d)

0.028 0.048 0.076 0.60

11.20 11.24 11.28 12.84 12.88

-1.2

-0.8

-0.4

0.0

0.4

0.8

1.2

1.6

T=5K

H=6T

Ir L2

Ir L3

UIrAl

XA

S In

ten

sit

y (

a.u

.)

Photon Energy (keV)

-0.04

-0.02

0.00

0.02

0.04

0.06

Ir

XM

CD

(a.u

.)

3.52 3.54 3.56 3.58 3.70 3.72 3.74 3.76 3.78

-8

-6

-4

-2

0

2

4

6

8

X

AN

ES

(a.u

.)

Photon Energy (keV)

-1.2

-0.9

-0.6

-0.3

0.0

0.3

0.6

0.9

1.2

-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0

-1.0

-0.5

0.0

0.5

1.0

T=5K

H//c-axis

U M4-edge

E0=3.726keV

-XM

CD

M4-e

dg

e

Magnetic Field (Tesla)

U

T=5K

H=3T

U M4

U M5

UIrAl

XM

CD

Strong XMCD at the L3-edge

Small XMCD at the L2-edge

Large Ir 5d orbital moment

aligned parallel to the spin

2p3/2 → 5d5/2,

3/2 2p1/2 → 5d 3/2

ANALYSIS COMBINING XMCD AND VSM MEASUREMENTS


VSM Data: Mtotal = 0.98B at 6 Tesla and 4.2K

• MIr(5d)= 0.076 B /Ir atom (sum over two Ir sites)

• MU(5f )= 0.92 B /U atom for nf=2 (U4+)

• MU(5f )= 0.62 B /U atom for nf=3 (U3+)

Mtotal= MU + MIr = 0.996 B

Al and U(6d) contributions are neglected

MESSAGE TO TAKE HOME


XMCDis very powerful spectroscopy tool

to unravel the microscopic origin of magnetism

Thank you for your patience and your attention !


x-ray and neutron science 2016 · 2016-09-23 · x-ray magnetic circular dichroism (xmcd) is...

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