Transcript Slide 1

A cobalt “divertissement”
Paolo G. Radaelli
ISIS Facility, Rutherford Appleton Laboratory and
Dept of Physics & Astronomy, University College London
Thanks to:
Maria Antonia Señaris Rodriguez, Univ. La Coruña
Laurent Chapon
Daniel Khomskii
Paolo G. Radaelli, Seillac, May 2006
2.0
LaCoO3
1.0
0.0
0
200
400
600
Temperature (K)
800
1000
1.
2.
Senaris-Rodriguez, M. A. & Goodenough, Journal of Solid State Chemistry 118, 323-336 (1995).
Itoh, M., Natori, I., Kubota, S. & Motoya, K. Journal of the Physical Society of Japan 63, 14861493 (1994).
Intermediate Spin
Goodenough
LaCoO3
LT
RT
LS
IS
HS
Co4+
HT
LS
IS
HS
Co4+
La1-xSrxCoO3
Intermediate Spin
Goodenough
LT
RT
HT
Structure, phase diagram etc.
1.
2.
3.
Raccah, P. M. & Goodenough, Physical Review 155, 932 (1967).
Senaris-Rodriguez, M. A. & Goodenough, Journal of Solid State Chemistry 118, 323-336 (1995).
Asai, K., Yoneda, A., Yokokura, O., Tranquada, J. M. & Shirane, G. Journal of the Physical Society
of Japan 67, 290-296 (1998).
XAS, LDA+U
1.
2.
3.
Abbate, M., Fuggle, J. C., Fujimori, A., Tjeng, L. H., Chen, C. T., Potze, R., Sawatzky, G. A., Eisaki,
H. & Uchida, S. Electronic-Structure and Spin-State Transition of LaCoO3. Physical Review B 47,
16124-16130 (1993).
Korotin, M. A., Yu, S., Solovyev, E. I. V. & Anisimov, V. I. Intermediate-spin state and properties of
LaCoO3. Physical Review B-Condensed Matter 54, 5309-5316 (1996).
Medarde, M., Dallera, C., Grioni, M., Voigt, J., Podlesnayak, A., Pomyakushina, E., Conder, K.,
Neisius, T., Tjernberg, O. & Barilo, S. N. Low-temperature spin-state transitioon in LaCoO3
investigated using resonant x-ray absorption at the Co K-edge. Physical Review B 73, Art. No.
054424 (2006).
EPS, INS
1.
2.
3.
Noguchi, S., Kawamata, S. & Okuda, K. Evidence for the excited triplet of Co3+ in LaCoO3.
Physical Review B 66, Art. No. 094404 (2002).
Ropka, Z. & Radwanski, R. J. 5D term origin of the excited triplet in LaCoO3. Physical
Review B 67, Art. No. 172401 (2003).
Phelan D., Louca D., Rosenkranz S. et al., PRL 96 Art. No. 027201 (2006)
Unit Cell Volume (Å3/f.u.)
59
La1-xSrxCoO3
57
55
x=0.00
x=0.20
x=0.05
x=0.25
x=0.10
x=0.30
x=0.15
0
200
400
600
Temperature (K)
800
1000
8
Q4 106
6
x=0.00
x=0.20
x=0.05
x=0.25
x=0.10
x=0.30
x=0.15
4
2
0
0
200
400
600
800
Temperature (K)
1000
DV (Å3/f.u.)
La1-xSrxCoO3
0.4
0.0
x=0.00
x=0.05
x=0.10
x=0.15
-0.4
-0.8
0
200
400
600
x=0.20
x=0.25
x=0.30
800
Temperature (K)
1000
DV (Å3/f.u.)
T=800K
0.4
1.5
1.0
0.2
0.5
T=8K
0.0
0.0
0.00 0.05 0.10 0.15 0.20 0.25 0.30
Sr content x
Magnetic Moment at 8 K (mB)
0.6
La1-xSrxCoO3
2.0
Oxygen Displacements (Å)
La1-xSrxCoO3
0.2
sperp
0.1
spar
0.0
0
200
400
600
800
Temperature (K)
1000
Atomic Displacement (Å)
0.15
T = 800 K
T = 295 K
T=8K
0.10
0.05
0.00 0.05 0.10 0.15 0.20 0.25 0.30
Sr content x
1.93 Å
2.16 Å
Louca, D., Sarrao, J. L., Thompson, J. D., Roder, H. & Kwei, G. H., Physical Review B 60, 10378-10382 (1999).
La0.75Ca0.25MnO3: a strongly polaronic system
P.G. Radaelli, M. Marezio, H. Y. Hwang, S-W. Cheong, and B. Battlog, PRB 54 (13), 8992-8995 (1996).
DLa-Olong (Å)
0.050
0.040
0.030
0.020
0.010
DLa-Oshort (Å)
0.000
0.000
-0.010
x=0.00
x=0.05
x=0.10
x=0.15
-0.020
-0.030
0
200
400
x=0.20
x=0.25
x=0.30
600
800 1000
Temperature (K)
Order parameter (tilt angle)
DQ 103
6
4
2
0
0
200
400
600
800
Temperature (K)
1000
Experimental tolerance factor
La1-xSrxCoO3
DTf103
0.0
-0.5
-1.0
Tf 
-1.5
0
200
d  La  O 
2  d  Co  O 
400 600 800
Temperature (K)
1000
• T1g symmetry
HOMO
• Contributions
from O2p only
• Non-bonding
character with La,
but antibonding
character with O.
• La-O distance
very sensitive to
O2p occupancy.
Medarde, M., Dallera, C., Grioni, et al. Physical Review B 73, Art. No. 054424 (2006).
7% decrease in O2p hole count from LT to RT.
Low Spin?
Co-3d
t2g6eg0 - LS
LT
Co-3d
t2g6eg1 L - LS
RT
O-2p
Co-3d
O-2p
t2g5 (1-x)eg1 - IS
HT
Co-3d
O-2p
t2g4eg2 - HS
La1-xSrxCoO3
Temperature (K)
1000
Co-3d O-2p
800
t2g4eg2 - HS
600
Co-3d O-2p
400
t2g5 (1-x)eg1 - IS
200
FM
0.1
Co-3d O-2p
0.2
Sr content x
t2g6eg1 L - LS
0.3
Complex magnetic structure
of YBaCo4O7
Laurent C. Chapon, John F. Mitchell, Paolo G. Radaelli
ISIS Facility, Rutherford Appleton Laboratory, Didcot, UK
Materials Science Division, Argonne National Laboratory, USA
Crystal structure
S=1.625
• Alternated stacking of Co Kagome sheets and Co triangular layer
• Half of the Co triangular units are “capped” by Co of the triangular layer
• Unique magnetic exchange topology
c(T)-Structural distortion
• 1st order structural phase
transition due to a strongly
under-bonded Ba ion
• Trigonal symmetry P31c
orthorhombic Pbn21
Ts(K)
320
Y
280
240
200
Tm
160
120
Lu
100
Yb
101
102
R (pm)
A. Huq, J.F. Mitchell et al., Journal of Solid State Chemistry, 179 1125 (2006)
103
104
Neutron diffraction vs. T
TN
T>110K, diffuse magnetic
scattering
T<110K, Long-range magnetic
Ordering with k=0
Neutron diffraction vs. T
1.2
T=115K
20
10
0
1.25
-1
1.50
Q (Å )
Short range correlations x=35
(102)
Integrated intensity (a. u.)
Intensity(arb. units)
T>110K
0.8
0.4
0.0
4
(012)
3
2
1
0
(101)
2
1
0
0
50
100 150 200 250 300
T(K)
M(Co) (mB)
4
2
0
2 (deg)
1(deg)
15
10
5
0
-5
-10
40
20
0
0 20 40 60 80 100
Temperature(K)