A cobalt divertissement Paolo G Radaelli ISIS Facility
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 La. Co. O 3 1. 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 La. Co. O 3 LT RT LS IS HS Co 4+ HT
LS IS HS Co 4+ La 1 -x. Srx. Co. O 3 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 La. Co. O 3. 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 La. Co. O 3. 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 La. Co. O 3 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 Co 3+ in La. Co. O 3. Physical Review B 66, Art. No. 094404 (2002). Ropka, Z. & Radwanski, R. J. 5 D term origin of the excited triplet in La. Co. O 3. 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 La 1 -x. Srx. Co. O 3 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 Q 4 106 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. ) La 1 -x. Srx. Co. O 3 0. 4 0. 0 x=0. 05 x=0. 10 x=0. 15 -0. 4 -0. 8 0 200 400 600 x=0. 25 x=0. 30 800 Temperature (K) 1000
DV (Å3/f. u. ) T=800 K 0. 4 1. 5 1. 0 0. 2 0. 5 T=8 K 0. 00 0. 05 0. 10 0. 15 0. 20 0. 25 0. 30 Sr content x Magnetic Moment at 8 K (m. B) 0. 6 La 1 -x. Srx. Co. O 3 2. 0
Oxygen Displacements (Å) La 1 -x. Srx. Co. O 3 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 = 8 K 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).
La 0. 75 Ca 0. 25 Mn. O 3: 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. 010 x=0. 05 x=0. 10 x=0. 15 -0. 020 -0. 030 0 200 400 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 La 1 -x. Srx. Co. O 3 DTf 103 0. 0 -0. 5 -1. 0 -1. 5 0 200 400 600 800 Temperature (K) 1000
• T 1 g symmetry HOMO • Contributions from O 2 p only • Non-bonding character with La, but antibonding character with O. • La-O distance very sensitive to O 2 p occupancy. Medarde, M. , Dallera, C. , Grioni, et al. Physical Review B 73, Art. No. 054424 (2006). 7% decrease in O 2 p hole count from LT to RT.
X Low Spin? Co-3 d t 2 g 6 eg 0 - LS
LT Co-3 d t 2 g 6 eg 1 L - LS RT O-2 p Co-3 d O-2 p t 2 g 5 (1 -x)eg 1 - IS HT Co-3 d O-2 p t 2 g 4 eg 2 - HS
La 1 -x. Srx. Co. O 3 Temperature (K) 1000 Co-3 d O-2 p 800 t 2 g 4 eg 2 - HS 600 Co-3 d O-2 p 400 t 2 g 5 (1 -x)eg 1 - IS 200 FM Co-3 d O-2 p 0. 1 0. 2 Sr content x t 2 g 6 eg 1 L - LS 0. 3
Complex magnetic structure of YBa. Co 4 O 7 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 • 1 st order structural phase transition due to a strongly under-bonded Ba ion • Trigonal symmetry P 31 c orthorhombic Pbn 21 A. Huq, J. F. Mitchell et al. , Journal of Solid State Chemistry, 179 1125 (2006)
Neutron diffraction vs. T TN T>110 K, diffuse magnetic scattering T<110 K, Long-range magnetic Ordering with k=0
Neutron diffraction vs. T T>110 K Short range correlations x=35
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