Photon Factory Activity Report 2004 #22 Part B (2005)
Electronic Structure of Condensed Matter

3A,10A/2003G183

Electronic structure of Co ions in Sr-substituted LaCoO3
1Takayasu HANASHIMA1, Norio SHIMIZU1, Takeharu MORI2, Satoshi SASAKI*1
Materials and Structures
Lab., Tokyo Inst. Tech., Nagatsuta, Yokohama 226-0803, Japan
2
KEK-PF, Tsukuba, Ibaraki 305-0801, Japan

Introduction
In the solid solution system of La1-xSrxCoO3, theelectronic structures of Co 3d electrons becomecomplicated, having two or more different spin states
5 13
such as low-spin (LS), intermediate spin (IS, T1; t2g eg )3+and high-spin (HS) states. When La in LaCoO3 is2+3+4+replaced by Sr , the constituent Co ion changes to Co
with doping of a hole. The existence of long-range
ferromagnetic order has been reported for the samples of0.2 ≤ x ≤ 1 in magnetization measurements and X-ray andneutron diffraction studies [1-3]. As increasing Sr
3+4+contents, the superexchange interaction of Co -O-Co
becomes more dominant and stronger than the4+4+3+3+3+
interactions of Co -O-Co and Co -O-Co , where Co
4+and Co ions are stable in the HS and LS states,
respectively [4].
A site-selective and valence-selective XMCD study isrequired for the Co K absorption edge to elucidate therelationship between magnetic property and crystal
structure in terms of the hybridization between the 3d and
4p states through the ligand 2p state. In this study, we
also calculate the electronic structures of both ground and1s core-hole states for the systems of La1-xSrxCoO3, byusing the discrete-variation Hartree-Fock-Slater method.
ExperimentalXANES and XMCD experiments were carried out on
the BL-3A. The horizontally polarized white X-rays weremonochromatized by the Si(111) double-crystal(H)monochromator. The beam size limited by a slit was 3(V)2x 2 mm at the sample position. The intensity after
transmitting through the sample was measured with 300
mm ionization chamber which was filled with 75% N2 +25% Ar gas. The difference in the absorption coefficientsfor right- and left-circularly polarized X-rays wasmeasured with spins parallel and antiparallel to thedirection of light travel. The incident beam was guided
into a synthetic single crystal of (001) diamond with athickness of 0.492 mm in order to produce circularly
polarized X-rays. A standard transmission setup wasused with the Faraday arrangement, where X-rays
irradiates the sample through a pair of pinholes in rareearth magnets in a magnetic field of 0.4 T. The
diffraction studies were carried out on the BL-10A.
Results and discussion
A negative XMCD peak B was clearly observed forpure LaCoO3 at E = 7.719 keV within the thresholdregion of the main edge. A positive XMCD peak C
appeared at E = 7.723 keV by Sr substitution of La in

LaCoO3 (x ≥ 0.2. A negative XMCD peak A was alsoobserved at the pre-edge, which can be explained as the4+hybridization with the neighboring Co in the dipoletransition. The dispersion-type XMCD signals at themain edge may be rationalized with the hypothetical
3+4+
double-exchange interaction between Co and Co . The
first-principles calculations reproduced well theexperimental spectra of X-ray magnetic circulardichroism (XMCD) at the Co K-absorption edge, where ahybridization of Co 3d and O 2p stabilizes a magnetic
state of La1-xSrxCoO3Fig. 1: XMCD spectra of La1-xSrxCoO3 (0 ≤ x ≤ 0.6) at
the Co K edge.
References[1] G.H. Jonker, J.H. Van Santen, Physica 19, 120 (1953).
[2] P. Ganguly et al., J. Phys. Cond. Mat. 6, 533 (1994).
[3] V.G. Sathe et al., J. Phys.:Cond. Mat. 8, 3889 (1996).
[4] H. Taguchi et al., Materials Res. Bull. 13, 1225 (1978).

* sasaki@n.cc.titech.ac.jp

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