Transcript Document

Electronic Structure and Transport Properties
of Iron Compounds: Spin-Crossover Effects.
Viktor Struzhkin
Collaborations
M. Eremets, I. Eremets
Max-Planck Institute, Mainz, Germany
A. Gavriliuk, I. Lyubutin
Institute of Crystallography, RAS, Moscow, RUSSIA
Optics and Theory
A. Goncharov, GL
S. Ovchinnikov
Institute of Physics, Siberian Branch of RAS, Krasnoyarsk, RUSSIA
NFS, XES
W. Sturhahn, J. Zhao, S. Kharlamova,
P. Chow, M. Y. Hu
APS, ANL, Argonne, USA
J. F. Lin
LLNL
Spins and Magnetism
P > Pc
P < Pc
Scope: electronic structure of Fe2+ and Fe3+
in octahedral sites
Theoretical approach
• In the Mott-Hubbard theory
charge fluctuations din djn  din-1 djn+1 are completely suppressed
due to strong exchange and Coulomb d - d interaction U
• J.Zaanen, G.Sawadzky, J.Allen [PRLett 1985]
showed that an another type of charge transfer () can be considered
din  din+1 L, where L – is a hole in p – valence band of anion
• Depending on the ratio of parameters, which are related to
hybridization Т, the system can be (from the point of view the nature of
the gap Еgap) :
1) Mott-Hubbard insulator d-d type U <  (Еgap U),
2) insulator (or semiconductor) with charge transfer
3) d – metal  < U and U < W/2
4) p – metal U <  and  < W
U >  (Еgap ),
Bandwidth- versus filling-controlled
metal-insulator transition
(Fujimori)
Mott-Hubbard transition under high pressure:
bandwidth control
Tanabe-Sugano diagram for Fe+3 ion and
Spin crossover
Fe3+ - LS (S = 1/2)
Fe3+ - HS (S = 5/2)
eg
d
t2g
10Dq
Usp
Magnetic collapse in transition metal oxides
Cohen, Mazin, Isaak, Science 1997
High-spin to low-spin transition
I. Jackson and A. E. Ringwood (1981)
ΔG = ΔE – PΔV + TΔS
ΔE = Nn{π - Δ(r)}, Δ~ Δ0(r0/r)5
For cubic (B1) FeO: Ptr=50 GPa
R. E. Cohen et al., MRS Symp proc. 1998
Intensity(a.u)
X-ray emission spectroscopy
as a local magnetic probe
F
e
S
a
t0
G
P
a
F
e
S
a
t0
G
P
a
2
F
e
S
a
t1
1
G
P
a
7
0
4
0
7
0
6
0
E
n
e
r
g
y
(
e
V
)
7
0
8
0
High-spin to low-spin
transition in FeS
K

1
,
3
J.-P. Rueff , C.-C. Kao,V. V. Struzhkin, J. Badro, J. Shu, R. J.
Hemley, and H. K. Mao , Phys. Rev. Lett. (1999)
Intensity(a.u)
X
r
a
y
K

F
e
)
e
m
i
s
s
i
o
n


s
p
e
c
t
r
a
,F
e
S
s
a
m
p
l
e
c
o
m
p
r
e
s
s
i
o
n
7
0
4
0
Intesity(a.u)
K

'
7
0
5
0
7
0
3
5 7
0
5
0 7
0
6
5
7
0
6
0
E
n
e
r
g
y
(
e
V
)
Intesity(a.u)
E
n
e
r
g
y
(
e
V
)
D
e
c
o
m
p
r
e
s
s
i
o
n
Intesity(a.u)
0
0
7
0
4
0
7
0
5
0
7
0
6
0
E
n
e
r
g
y
(
e
V
)
2
4
6
8 1
0 1
2
P
r
e
s
s
u
r
e
(
G
P
a
)
Spin-crossover transition in ferropericlase
J. Badro et. al., Science (2003) Mg0.83Fe0.170
Nuclear inelastic scattering set-up
(W. Sturhahn, E. Alp, M. Hu)
Log( Intensity )
41 GPa
21
16
0.7
nonmagnetic
magnetic
40
60
80
100
5
120
Time, nsec
t
KB
mirrors
APD
200
nsec
HRM
M
APD
Intensity (cts/sec)
T/TN
P (GPa)
1.62
0.9
1.37
5.6
1.22
10
1.07
16
0.98
20
0.85
28
0.75
36
0.68
42
0.63
48
-60 -40 -20
0
20
Energy (meV)
t
40
60
FeBO3 Mössbauer spectroscopy and NFS (Lyubutin et al.)
57
Fe B O3
T = 296 K
55.0
T = 77 K
55.2
50.5
50.0
48.6
Intensity (a.u.)
46.6
39.2
27.5
42.0
40.8
39.0
36.0
35.0
9.2
18.9 GPa
2.3 GPa
-10
-5
0
Velocity (mm/s)
5
10
0
40
80
120
Time (ns)
160
10Dq
Reduced radiative conductivity
of low-spin (Mg,Fe)O in the lower mantle
A. Goncharov, V. Struzhkin, and S. Jacobsen
The observed changes in absorption are in contrast to
prediction and are attributed to d-d orbital charge transfer in
the Fe2+ ion. The results indicate low-spin (Mg,Fe)O will exhibit
lower radiative thermal conductivity than high-spin (Mg,Fe)O,
which needs to be considered in future geodynamic models of
convection and plume stabilization in the lower mantle.
Theory
Comparison of Mössbauer and
X-ray emission results for FeO
M. P. Pasternak et al . Phys. Rev. Lett.(1997)
J. Badro et al. Phys. Rev. Lett. (1999)
NFS FeO (wüstite)
1=log(10)
873
50 GPa
823
200 GPa
175 GPa
Log(Intensity)
773
673
573
135 GPa
112 GPa
80 GPa
303 K
47 GPa
26 GPa
0
50
Delay (nsec)
100
20
40
60
80
100
Time (nsec)
120
140
160
Magnetic phase diagram of FeO
T (K)
3000
Geotherm
2000
D"
Nonmagnetic-NaCl type
Magnetic?-NiAs type
1000
Core-mantle boundary
4000
Magnetic-rhombohedral
0
0
20
40
60
80
100
Pressure (GPa)
120
140
Insulator-metal transition in FeO
41 GPa
AF Insulator
16
113 GPa
Metal (FM?)
22 GPa
14
0.20
56 GPa
12
ln(R)
Ea (eV)
0.15
10
0.10
90 GPa
8
110 GPa
0.05
6
125 GPa
0.00
4
5
0
50
100
Pressure (GPa)
150
10
15
1000/T (K-1)
20
Fe3+ Samples:
Singe crystals
enriched with
the Fe-57
isotope
- Fe B O3
- R Fe3 (BO3)4 (R = Gd)
- Y3 Fe5 O12
Y3Fe5O12
19 GPa
0 GPa
Electronic transition
41 GPa
13 GPa
Changes in the crystal color under
pressure increase and decrease
50 GPa
32 GPa
FeBO3
0.95
Structural, magnetic, electronic
and spin transitions
at high pressures
T = 295 K
0.90
V / V0
FeBO3
1.00
0.85
0.80
0.75
at 53 GPa  collapse of the
unit-cell volume by ~ 9 %
0.70
0
10
20
30
40
50
60
70
80
Pressure (GPa)
3.0
2.5
E (eV)
FeBO3
C
T = 295 K
at P = 46 GPa the insulatorsemiconductor transition
C1
2.0
B
1.5
A
1.0
0.5
0.0
0
10
20
30
40
50
60
70
at P = 46 GPa
magnetic collapse
with the
HS  LS transition
80
50
2.0 57
40
1.6
QS (mm/s)
Hhf (Tesla)
Pressure (GPa)
30
20
57
FeBO3
10
T = 296 K
0
0
10
20
30
40
50
Pressure (GPa)
60
FeBO3
T = 296 K
1.2
0.8
0.4
0.0
-0.4
-0.8
0
10
20
30
40
50
Pressure (GPa)
60
GdFe3(BO3)4
3
V (A )
Structural, electronic
and spin transitions
at high pressures
T = 296 K
560
520
480
440
400
0
10
20
30
40
50
at 26 GPa  collapse of the
unit-cell volume by ~ 8 %
60
Pressure (GPa)
GdFe3(BO3)4
3.0
Eopt (eV)
T = 296 K
C
2.5
at P = 43 GPa the insulatorsemiconductor transition
2.0
1.5
at P = 43 GPa
the HS  LS transition
1.0
0.5
0
10
20
30
40
50
60
Pressure (GPa)
2.4
0.14
GdFe3(BO3)4
0.12
T = 295 K
2.0
0.10
1.6
Isat / I0
QS (mm/s)
GdFe3(BO3)4
600
1.2
0.8
0.08
0.06
GdFe3(BO3)4
0.04
0.4
T = 295 K, ~ 12 m
0.02
0.0
0
10
20
30
40
Pressure (GPa)
50
60
0.00
5
10
15
20
25
30
35
40
45
Pressure (GPa)
50
55
Y3Fe5O12
Structural, magnetic, electronic
and spin transitions
at high pressures
0.95
T = 295 K
V / V0
0.90
0.85
0.80
amorphization
0.75
at 48 GPa  srtuctural
amorphyzation
0.70
0
10
20
30
40
50
60
Pressure (GPa)
Y3Fe5O12
3.0
E (eV)
2.5
T = 295 K
at P = 50-55 GPa the
insulator- metal transition
2.0
B-band
1.5
A-band
1.0
at P = 48 GPa
magnetic collapse with the
HS  LS transition
0.5
0.0
0
10
20
30
40
50
60
Pressure (GPa)
Hoct
50
2.0
Y3Fe5O12
T = 300 K
1.6
40
Htet
30
QS (mm/s)
H (Tesla)
Y3Fe5O12
1.00
Y3Fe5O12
20
T = 300 K
10
1.2
0.8
0.4
oct
0.0
tet
-0.4
0
0
10
20
30
40
50
Pressure (GPa)
60
-0.8
0
10
20
30
40
50
60
Pressure (GPa)
70
80
Bi Fe O3 : Multiferroic
BiFeO3 - belongs to ferro-magneto-electric materials
(multiferroics) which have both a spontaneous
electrical polarization and a spontaneous magnetization.
Between known multiferroics, it has a record high
the antiferromagnetic Neel temperature (TN = 643 K)
and the ferroelectric Curie temperature (TC = 1083 K)
BiFeO3
Electronic transition from the
insulating to highly conducting state.
Mott ?
7.2 GPa
54.5 GPa
BiFeO3 Pressure – temperature dependence
of resistivity
8
10
9
10
8
10
7
10
6
10
5
10
4
10
3
10
2
41.5 GPa
BiFeO3
7
BiFeO3
T = 295 K
6
46.1
5
lg(R)
R ()
10
10
4
47.8
3
10
20
30
40
P (GPa)
50
60
At 40 – 55 GPa the
resistance drops by 107
(metallization)
70
2
51.5
53.4
54.5
1
0
0.000 0.005 0.010 0.015 0.020 0.025 0.030
-1
1 / T (K )
Structural, magnetic, electronic
and spin transitions
at high pressures
BiFeO3
360
T = 295 K
340
3
V (A )
Bi Fe O3
380
320
300
near 45 GPa  srtuctural
transition
280
260
0
10
20
30
40
50
60
70
Pressure (GPa)
at P = 45-55 GPa the
insulator- metal transition
BiFeO3
2.0
Egap (eV)
T = 295 K
1.5
at P = 47 GPa
magnetic collapse with the
HS  LS transition
1.0
- compression
- decompression
0.5
0.0
0
10
20
30
40
50
60
70
Pressure (GPa)
BiFeO3
T = 295 K
8
10
7
H (Tesla)
R ()
NFS
50
10
6
10
5
10
4
XES
1,0
40
0,8
57
Bi FeO3
30
T = 295 K
20
0,6
BiFeO3
0,4
T = 295 K
10
10
0,2
3
0
10
0,0
0
2
10
1,2
60
Isat / I0
9
10
0
10
20
30
40
50
Pressure (GPa)
60
70
10
20
30
40
50
Pressure (GPa)
60
70
0
10
20
30
40
50
Pressure (GPa)
60
70
Theoretical approach
• S. G. Ovchinnikov [JETP Letters, 2003]
Main parameter  is the effective Hubbard energy Ueff
Ueff = E0(d 4) + E0(d 6) - 2 E0(d 5)
LPP 
HPP 
P < Pc 
P > Pc 
S=2
S=1
S=2
S=0
S = 5/2
S = 1/2
ELECTORON STRUCTURE
of FeBO3 and GdFe3(BO3)4
[S.G. Ovchinnikov and S.A. Kharlamova, JETP Letters, 2003; 2004]
SEC for Fe:
а) d - d - transitions
b) charge transfer transitions p6d5  p5d6 
electron creation Fe3+  Fe2+:
с = E (5Т2, d6) – E (6A1, d5)
hole creation Fe3+  Fe4+:  = E0 (6A1,d5) – E0 (6A1,d4)
By Raccah parameters :
с = d + 5 A + 14 B – 0.4 
 = d + 4 A – 14 B + 0.6 
Then the Hubbard effective parameter is:
Ueff = c –  = А + 28 В –  = 4.2 eV
7
ELECTRON STRUCTURE of FeBO3 and GdFe3(BO3)4 in
MULTIELECTRON MODEL at AMBIENT and HIGH PRESSURE
S.G.Ovchinnikov. JETP Lett. (2003)
Density of states, N (E)
v
c
F
P < PC
The effective Hubbard
parameter:
Ueff = c -  = E0(d4) +E0(d6) 2E0(d5)
c
v
~
~
c
v
PPc
S=2
S=2
S=5/2
P > PC
PPc
S=1 S=0 S=1/2
Ueff = c -  = А + 9В -7С  1.45 eV
Ueff
c
v
Energy, E
Density of electronic states of
GdFe3(BO3)4 in within multi-electronic
p - d model at ambient and high
4.2
1.45
Р
Р
Theoretical approaches
Fe3+
Fe2+
• S. G. Ovchinnikov [JETP Letters, 2003]
V
C
P < PC
N()
UHS
2p-B
2p-O

F
V C
N( )
ULS
2p-O
F
P > PC
2p-B

FeO?
Bandwidth- versus filling-controlled
metal-insulator transition
(Fujimori)
HS-LS
U-control