Exotic High Spin Value Compounds

1
Exotic High Spin Value Compounds

• M. Rotter, A. Barcza IPC, University of Vienna,
  Austria
• A. Devishvili, A. Stunault, ILL, Grenoble, France
  
• M. Doerr, IFP TU-Dresden, Germany
• J. Prokleska, J. Vejprarova, Charles University,
  Prague, The Czech Republic
• B. Beuneu, LLB, Saclay, France
• M el Massalami, UFRJ, Brazil
• J. Jensen, University Copenhagen, Denmark
• T. Takanori, University of Hiroshima, Japan
• Y. Narumi, K. Katsumata, ISSP, Tokyo, Japan

2
?
?
Austria
3
??
?
??
Johann Strauss
Vienna
Ludwig Boltzmann
Erwin Schrödinger
4

• Introduction to high spin value compounds
• Measurement techniques
• The Standard Model
• The Magnetoelastic Paradox (MEP)
• Exotic high spin systems
• Magnetism of GdRu2Si2 and Gd5Ge3
• Summary and Outlook

5

• Fundamental interest
• largest spin value in periodic table
• Technical interest
• Giant Magnetocaloric Effect
• Giant Magnetostriction

6
Measurement Techniques
7

• Magnetometry (VSM)
• Magnetic X-ray Scattering
• (single crystal)

Heat Capacity

• Magnetic Neutron Diffraction

8
GdCu2
TN 42 K M ?010 TR 10 K q (2/3 1 0)

Magnetic Structure from Neutron Scattering
Rotter et.al. J. Magn. Mag. Mat. 214 (2000) 281
9
Magnetostriction
10
Magnetostriction
Capacitance Dilatometry
X-ray Powder Diffraction

• Anisotropic Effects on
• Polycrystals (Expansion,
• Symmetry-Changes)
• bad resolution (10-4 in dl/l)

• Good resolution (10-9 in dl/l)
• 45 T Magnetic Fields - forced magnetostriction
  
• requires single crystals

Rotter et.al. Rev. Sci. Instr. 69 (1998)
2742 (patent by M Rotter, optional use in PPMS,
VTIs,... operated at 7 institutes in A, CH, D,
CZ, Brazil, US)
11
STANDARD MODEL OF RARE EARTH MAGNETISM
RKKY
Dipolar
Crystal Field
Zeeman term
single ion
single ion
two ion
0-101 meV
101-10-1meV
101-10-1meV
10-3meV
dep. L
dep. on S gt de Gennes factor
In order to effectively study the exchange
interactions one need to focus research on
compounds having no crystal field.
12
STANDARD MODEL OF RARE EARTH MAGNETISM
Crystal Field Effect
NO Crystal Field Effect
Sm,Er, Tm,Yb ?gt0
Ce,Pr,Nd, Tb,Dy,Ho ?lt0

Gd3,Eu2 ?0

e-
e-


L0
L?0
Spherical 4f-Charge Density
Distortion of 4f Charge Density
13
STANDARD MODEL OF RARE EARTH MAGNETISM
Exchange
Dipolar interaction
RKKY
14
STANDARD MODEL OF RARE EARTH MAGNETISM

• microscopic origin of magnetostriction
• strain dependence of magnetic interactions

1) Single ion effects 2) Two ion
effects ? Crystal Field Striction ?
Exchange Striction
spontaneous magnetostriction
forced magnetostriction
kT gtgt?cf
kT lt?cf
H
15
Formalism to calculate the striction values ? ?
..
with.....
results in
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Exchange striction on a Square Lattice
Ferromagnet J1gt0 dV/Vlt0
No distortion (dJ1/de)
17
Anti-Ferromagnet with NN exchange J1lt0 dV/Vgt0
No distortion (dJ1/de)
18
How to detect a symmetry breaking distortion ?
THE MAGNETOELASTIC PARADOX ?? Antiferromagnets
with L0 below TN Symmetry breaking distortions
are expected but have NOT been found
Intensity
2theta
.... ALL Experiments symmetry breaking
distortion ? lt10-4
19
GdNi2B2C
TN 20 K M010 ltTR 14 K M0yz q
(0.55 0 0)
small magnetostriction, therefore
cap.-dilatometry ....
20
GdNi2B2C
Da/a
TN 20 K M010 ltTR 14 K M0yz q
(0.55 0 0)
10-4
Magnetic Propagation Vektor q (0.55 0 0)
21
GdNi2B2C
.... FWHM determined by fitting
?
At H0 Domains ?
Powder Xray Diffraction
distortion e3x10-4 would lead to FWHM
(204) 0.1 FWHM (211) 0.05
at H0 no distortion can be found (magnetoelastic
paradox)
22

McPhase - the World of Rare Earth Magnetism
McPhase is a program package for the calculation
of magnetic properties of rare earth based
systems.
          Magnetization           
           Magnetic Phasediagrams
    Magnetic Structures    
       Elastic/Inelastic/Diffuse
                                             
Neutron Scattering
                                            
Cross Section
www.mcphase.de
23
The magnetic Hamiltonian
Isotropic exchange (RKKY,...)
Classical Dipole Interaction
Zeeman Energy
24
(No Transcript)
25
AM!
Hmag McPhase
?
T2 K
26
The Magnetoelastic Paradox .... demonstrated
at GdNi2B2CRotter et al. EPL 75 (2006) 160
Orthorhombic Distortion
?
Exchange Striction Model
Capacitance Dilatometry
Standard Model of RE Mag ... McPhase Simulation
27
Double Q structure
Orthorhombic Distortion
b

T
2 K
Exchange Striction Model
Exchange Striction Model
e
b
-
e
a

a
Capacitance Dilatometry
... is more stable than single q The
Magnetoelastic Paradox explained !? J.
JensenM. Rotter 2007, PRB submitted
m
H
a
(kOe)
0
Standard Model of RE Mag ... McPhase Simulation
gt
lt
-
gt
lt
-
e
e
J
J
J
J



H
H
,
)
010
(
,
)
100
(
T
i
i
T
i
i
bb
aa
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Anisotropic Spontaneous Magnetostriction
Ferromagnet Antiferromagnet
e
TC(N)K
Spontaneous Magnetoelastic Effects in Gd
Compounds A. Lindbaum, M. Rotter Handbook of
Magnetic Materials Vol 14 (Buschow, Elsivier,NL)
29

• GdNi2B2C large distortion at small magnetic
  fields
• ... is this common to all isotropic
  AFM ?
• ... implication on magnetostrictive
  technology ?

Magnetostrictive Position Sensor
Magnetostrictive ultrasonic dental transducer
Magnetostrictive actuator
Magnetostrictive Liquid-Level Sensor
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Status of Research on Magnetostriction in Gd
based Antiferromagnets. Systems with a symmetry
breaking magnetic propagation vector and large
spontaneous magnetostriction demonstrate the
existence of the magnetoelastic paradox and are
marked by "MEP". Symmetry Magnetic
Anisotropic/ Single Forced /
Propagation isotropic(dV/V) Crystal
Magneto- Neel Spontaneous available
-striction Temp.(K) Magnetostriction
(10-3) GdIn3 cub./43 12 (1/2 1/2 0) 13 MEP!
0.0/-0.3 14 yes GdCu2In cub./10 (1/3 1 0)
R18 0.0/-0.1 15 GdPd2In cub./10 16
0.0/0.0 15 GdAs cub./25 (3/2 3/2 3/2) 17,
18, 19 17no MEP ? GdP cub./15 (3/2 3/2 3/2)
17 17 GdSb cub./28 (3/2 3/2 3/2) 20 ?
21, 22no MEP? Yes work in
progress GdSe cub./60 (3/2 3/2 3/2) 20 GdBi
cub./32 (3/2 3/2 3/2) 20 21no MEP ? GdS
cub./50 (3/2 3/2 3/2) 20 EuTe cub./9.8 (3/2
3/2 3/2) 23 23 GdTe cub./80 (3/2 3/2 3/2)
20 GdAg cub./133 (1/2 1/2 0) 24 GdBe13
cub./27 (0 0 1/3) 25 Gd2Ti2O7 cub./1 (1/2
1/2 1/2) 26 yes GdB6 cub./16 (1/4 1/4 1/2)
27 yes Gd2CuGe3 hex./12 28 GdGa2
hex./23.7 (0.39 0.39 0) 29 GdCu5 hex./26
(1/3 1/3 0.22) 29 Gd5Ge3 hex./79 30 (0.35
0 0) work in progress yes work in
progress Gd7Rh3 hex./140 31, 32 4.0/0.0 Gd2PdS
i3 hex./21 33 work in progress yes GdCuSn
hex./24 (0 1/2 0) 34 MEP! 1.9/-0.5
35 GdAuSn hex./35 34 (0 1/2 0) 36 GdAuGe
hex./16.9 37 GdAgGe hex./14.8 38 GdAuIn
hex./12.2 38 GdAuMg hex./81 39 GdAuCd
hex./66.5 40 (1/2 0 1/2) 40 GdAg2 tetr./23
(1/4 2/3 0) R12 MEP! 1.2/0.0 R19 Gd2Ni2-xIn
tetr./20 R19 0.8/0.0 R19
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Symmetry Magnetic Anisotropic/ Single
Forced / Propagation isotropic(dV/V)
Crystal Magneto- Neel Spontaneous
available -striction Temp.(K)
Magnetostriction (10-3) Gd2Ni2Cd tetr./65
41 Gd2Ni2Mg tetr./49 42 Gd2Pd2In tetr./21
43 GdNi2B2C tetr./20 (0.55 0 0) 44 MEP!
0.1/0.0 R19, R20 yes R4 GdAu2 tetr./50
(5/6 1/2 1/2) R12 0.0/0.0 R19 GdB4
tetr./42 (1 0 0) 45 GdRu2Si2 tetr./47 46
(0.22 0 0) MEP! -0.6/-0.8 yes in
progress GdRu2Ge2 tetr./33 46 work in
progress work in progress GdNi2Si2 tetr./14.5
(0.21 0 0.9) 47 GdNi2Sn2 tetr./7
48 GdPt2Ge2 tetr./7 48 GdCo2Si2 tetr./45
48 GdAu2Si2 tetr./12 (1/2 0 1/2)
R12 GdPd2Ge2 tetr./18 48 GdPd2Si2
tetr./16.5 49 GdIr2Si2 tetr./82.4
49 GdPt2Si2 tetr./9.3 49 (1/3 1/3 1/2)
50 GdOs2Si2 tetr./28.5 49 GdAg2Si2 tetr./10
48 GdFe2Ge2 tetr./9.3 51, 52 GdCu2Ge2
tetr./15 51 GdRh2Ge2 tetr./95.4 51 GdRh2Si2
tetr./106 49 GdCu2Si2 tetr./12.5 (1/2 0 1/2)
47 GdPt3Si tetr./7.5 53 work in
progress GdCu(FeB) orth./45 (0 1/4 1/4) 54
19/-2 54 Gd3Rh orth./112 55 MEP ? 6.4/2.1
56 Gd3Ni orth./100 57 MEP ? 4.5/2.9
56 Gd3Co orth./130 58, 59 GdSi2
orth.(lt818K)/? 60 GdSi orth./55 61 work in
progress work in progress yes work in
progress GdCu6 orth./16 62 work in
progress GdAlO3 orth./3.9 63 GdBa2Cu3O7
orth./2.2 (1/2 1/2 1/2) 64 65 GdPd2Si
orth./13 66
32
The following compounds are not expected to show
a change in lattice symmetry at the transition
from the paramagnet to the antiferromagnet,
because the propagation vector does not break the
symmetry of the lattice and there is only one
atom in the primitive crystallographic unit cell.
Therefore they cannot exhibit the magnetoelastic
paradox. Symmetry Magnetic Anisotropic/
Single Forced / Propagation
isotropic(dV/V) Crystal Magneto- Neel
Spontaneous available -striction Temp.(K)
Magnetostriction (10-3) GdNi2Ge2 tetr./27
(0 0 0.79) 67 GdCo2Ge2 tetr./37.5 51 (0 0
0.93) 68 In the following compounds the
propagation does not break the crystal symmetry
and there are more than one atom in the primitive
crystallographic unit cell. In this case it
depends on the relative orientiation of the
moments in the unit cell, whether a symmetry
breaking distortion is predicted by the exchange
striction model or not. Therefore these compounds
can in principle exhibit the magnetoelastic
paradox although the propagation does not break
the crystal symmetry of the lattice. Symmetry
Magnetic Anisotropic/ Single Forced
/ Propagation isotropic(dV/V) Crystal
Magneto- Neel Spontaneous available
-striction Temp.(K) Magnetostriction
(10-3) Gd2Sn2O7 cub./1 (0 0 0) 69
yes Gd2In hex./100 (0 0 1/6) 70 0.0/0.0
R19 Gd2CuO4 tetr./6.4 (0 0 0) 71 GdCu2
orth./42 (1/3 0 0) R21 4.6/0.6 72 yes
R22 Gd5Ge4 orth./130 11 (0 0 0) 73
?/lt0.1 74 yes 74 GdNi04Cu06 orth./63
(0 0 1/4) 75 0.0/0.8 76 Gd2S3 orth./10
77 (0 0 0) 78 0.0/0.0 79 yes
79 GdNiSn orth./11 80 (0 0 0) 81 yes
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Our Research Program
MXD-Magn. X-ray diff., MP-Magn. phase inv.,
MS-magnetostrict., TE-Thermal exp., Cp-Specific
heat.
34
GdRu2Si2
Gd Ru Si
35
GdRu2Si2
?
?
?
No sign of distortion of the tetragonal plane !
36
GdRu2Si2

• Strategy
• Bulk measurements
• Neutron Powder fit
• Magnetic X-ray
• McPhase simulation
• Simulation vs. Experiment comparison

Thermal expansion
Magnetostriction
Susceptibility
Magnetization
HC
TN
Tr
T2K
37
GdRu2Si2

• Strategy
• Bulk measurements
• Neutron Powder fit
• Magnetic X-ray
• McPhase simulation
• Simulation vs. Experiment comparison

Thermal expansion
Magnetostriction
HC
TN
H100 T2K
Magnetic Fielda(T)
38
GdRu2Si2

• Strategy
• Bulk measurements
• Neutron scattering
• Magnetic X-ray
• McPhase simulation
• Simulation vs. Experiment comparison

39
GdRu2Si2

• Strategy
• Bulk measurements
• Neutron Powder fit
• Magnetic X-ray
• McPhase simulation
• Simulation vs. Experiment comparison

moment direction
propagation vector weak temperature dependance
T2K-38K, moments in bc-plane T38K-47K, c
component gets larger than b
40
GdRu2Si2
110

• Strategy
• Bulk measurements
• Neutron Powder fit
• Magnetic X-ray
• McPhase simulation
• Simulation vs. Experiment comparison

010
Ru
Gd
Si
001
41
GdRu2Si2 isotropic model

• Model summary
• Tn
• Hc
• -Susceptibility
• -No transition
• Hca, Hcc
• Magnetization
• Dipolar model prediction gtmoment b
• experiment shows moment c

42
GdRu2Si2
43
GdRu2Si2 anisotropic model 1

• Model summary
• Tn
• Hca ,Hcc
• -Susceptibility
• -No transition
• Magnetization
• Anisotropic RKKY (all neighbors)

44
GdRu2Si2 anisotropic model 2
Model summary Tn Hca ,Hcc Magnetization Trans
ition presented -Susceptibility -Anisotropic
J001 only.
45
GdRu2Si2 neutron diffraction
(002)t (101)-t
(011)t (110)-t
(101)t
?(0.222 0 0)
46
GdRu2Si2 magnetoelastic contribution
47
GdRu2Si2 magnetostriction and entropy
Anisotropic model 1
Anisotropic model 2
Magnetostr. Exp.
H100
eaa- ebb
eaa ebb
48
Biquadratic exchange
49
GdRu2Si2 with biquadratic exchange
Model summary Tn Hca ,Hcc Magnetization Trans
ition presented Susceptibility - Magnetostriction
eaa- ebb
eaa ebb
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GdRu2Si2 double q
ltJJ100gt-ltJJ010gt
ltJJ100gtltJJ010gt
eaa- ebb
single q FE-4.63224 meV/ion (9x1x1) PV 0.2222 0
0 vs double q FE-4.78422 meV/ion
(9x1x9) PV0.2222 0 0
eaa ebb
51
GdRu2Si2 double q
Work in progress
52
Gd5Ge3 .a new irreversibility !

• compare to Gd5Ge4
• - giant magnetocaloric effect
• - giant magnetostriction !
• Crystal structure
• hexagonal lattice (P63 /mcm)
• Gd3 ion two cryst. sites (4d, 6g)
• a 8.543 Å , c 6.403 Å
• Magnetic structure
• TN 76 K, ? (0.35 0 0)
• T 52 K (afm modification)
• moments perpendicular to c-axis
• (easy c-plane)
• weak afm exchange

ac -plane
53

• Magnetostriction
• magnetostructural irreversibility
• at about 12 T
• irreversible shape switching
• strain lt 10-3
• magnetovolume effect ?
• increase of magnetoelastic energy
• magnetic saturation at 30 T

Recovery by heating (E ? 4 meV)
54

• Magnetostriction
• irreversibility is strongly
• temperature dependent !

100 K
T 4 K ....
60 K
40 K
20 K
55

• Magnetostriction
• Phase diagram
• Magnetization (H c, hard-direction)
• small irreversibility
• effect

56
Summary and outlook
???

• double-q structures explain the magnetoelastic
  Paradox
• the large anisotropy in some Gd compounds may be
  due to anisotropy in the two ion interactions
• biquadratic interactions are necessary to
  explain the temperature dependence of the
  susceptibility in GdRu2Si2 and GdNi2B2C. Is this
  a universal feature ?
• GdNi2B2C large distortion at small fields - is
  this common to other high spin value AFM ? ...
  implication on magnetostrictive technology ?
• Gd5Ge3 shows a magnetocrystalline irreversibility
  (0.1 )
• to be investigated by high-field magnetic
  x-ray/neutron scattering
• Magnetoelastic Coupling long wave length limit
  of electron phonon interaction ... relevance for
  superconductivity ?

57
ToDo(FWF project)
New Methods

• Imaging of AFM domains
• with XRMS

??

• More Experiments
• Powder X-ray Diffraction
• Magnetic Neutron / X-ray Scattering
• Dilatometry in high Fields

• More Theory
• Apply Standard model of RE Magnetism
• Ab initio Calculation on MEP

• Anisotropy Measurements
• by ESR
• Hot Neutron Scattering in
• high magnetic fields

58
Thanks to
??
M. Doerr M. Loewenhaupt M. Zschintzsch M.
Frontzeck
A. Stunault A. Hiess A. Devishvili J.
Rodrigez-Carvanjal B. Ouladiaf G. Cuello.
A. Barzca A. Lindbaum
Charles University Prague
H. Michor H. Müller G. Hilscher
J. Prokleska J. Vejprarova
M.el Massalami
Y. Narumi K. Katsumata
A. Kreyssig
B. Beuneu P. Ambrouse
T. Takanori
. and thanks to you !
59
GdCuSn
TN 24 K q(0 ½ 0)
60
GdAg2
TN 22.7 K ltTR121.2K
M001 ltTR210.8K M110

GdAu2 TN 50 K
q(0.362 0 1)
61
Gd3Ni
Gd3Rh TN112 K
TN100 K
Large magnetostrictive effects on lattice
constants but NO distortion
62
Volume Magnetostriction
Spontaneous Magnetoelastic Effects in Gd
Compounds A. Lindbaum, M. Rotter Handbook of
Magnetic Materials Vol 14 (Buschow, Elsivier,NL)
63
Paramagnetic Rare Earth Magnetic Shape Memory
Alloys- RMSM

• M. Rotter, S. Raasch, M. Doerr, A. Kreyssig,
• J. U. Hoffmann, M. Loewenhaupt

64
Crystallographic Structure of RCu2 (R rare
earth) ...
structure is close to hexagonality
65
... provides the possibility of three twin
variants
hexagonal plane is distorted
66
... provides the possibility of three twin
variants

• application of magnetic field
• along easy axis of new variant
• RMSM effect observed in paramagnet

µ0H
67
Magnetization DyCu2
H c
H c
Giant Magnetostriction
68
Field dependence of microstructural conversion
... conversion field of trained Tb0.5Dy0.5Cu2
samples
69
RMSM - State of the Art

• MSM effect exists at most RCu2 compounds
• transition field µ0H gt 2.2 T
• conversion temperature
• Tconversion varies with field (10 K ... gt80
  K)
• independent from magnetic ordering
• RCu2 compounds are antiferromagnets
• magnetostrain 1 .. 3

70
Outlook - further experiments are desirable

• look for other RMSMs, e.g. RCu2 ? RM2
• general temperature range ?
• general conversion field?
• modeling of RMSM systems
• RMSM poly-crystals in a polymer matrix

71
Thermoelectricity - the Figure of Merit
S ....... Seebeck Coefficient ? .......
Electrical Resistivity ? ....... Thermal
Conductivity

• Note
• Mathiessens Rule ? ?e ?p
• Wiedemann Franz Law ?eL0T/?

?increase Z by decreasing ?p !
72
Skutterudite StructureRExT4Sb12
Unfilled CoSb3 , CoAs3 , RhP3 , RhSb3 , ...
Filled BaCo4Sb12, PrFe4P12, YbCo4Sb12, ...
.... rattling modes ? .....Orbitons ?
73
Movement of Atoms Sound, Phonons
Brockhouse 1950 ...
p/a
Phonon Spectroscopy 1) neutrons
2) high resolution X-rays
74
Movement of Spins - Magnons
153
a
T1.3 K
Bohn et. al. PRB 22 (1980) 5447
75

• Movements of Atoms Sound, Phonons

1970 Movement of Spins Magnons
? Movement of Orbitals Orbitons
a
a
torbiton
torbiton
Description quadrupolar (higher order)
interactions
76
GdRu2Si2
Gd Ru Si
TN47 K q(0.22 0 0)
Note e4.10-5 ... ?FWHM0.0015 deg
77
(No Transcript)
78
GdSb
Structure NaCl type Type II AFM order
q(111) TN24.4 K
79
Normal thermal Expansion
Anharmonicity of lattice dynamics
anharmonic Potential
Harmonic potential
with Debye function

Small contribution of band electrons
80
Forced Magnetostriction
Crystal Field
Exchange - Striction

L?0
L0, L?0
H ?lt0
H

e-
H ?gt0

Gd3, S7/2, L0
81
Theory of Magnetostriction
Crystal field
Exchange
with