Photon Factory Activity Report 2005 #23 Part B (2006)
Electronic Structure of Condensed Matter

2C/2005S2-002
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Robust Ti states in SrTiO3 layers ofLa0.6Sr0.4MnO3/SrTiO3/La0.6Sr0.4MnO3 junctions
H. Kumigashira1*, R. Hashimoto1, A. Chikamatsu1, M. Oshima1, M. Lippmaa2,H. Wadati3, A. Fujimori3, M. Kawasaki4, and H. Koinuma5
1

Department of Applied Chemistry, The Univ. of Tokyo, Tokyo 113-8656, Japan
Institute for Solid State Physics, The Univ. of Tokyo, Kashiwa 277-8581, Japan3
Department of Physics and Department of Complexity Science and Engineering,
The Univ. of Tokyo, Kashiwa 277-8561, Japan
4Institute for Materials Research, Tohoku Univ., Sendai 980-8577, Japan
5National Institute for Materials Science, Tsukuba 305-0047, Japan
2Introduction
Spin tunnel junction based on half-metalic materials
has a great potential for future magnetroelectronic
applications, such as tunneling magnetoresistance (TMR)
devices [1]. Hole doped manganese oxide La0.6Sr0.4MnO3(LSMO) is one of the most promising materials for TMR
devices owing to their half metallic nature. However, theperformance of TMR devices based on theLSMO/SrTiO3(STO)/LSMO tunneling junction, in which
STO is used as a tunnel barrier, is far below what isexpected from the high spin polarization, suggesting the“dead layer” formation at heterointerfaces between
LSMO and STO [2]. In order to investigate an interfacial
electronic structure, we have performed Ti 2p core-level
photoemission and x-ray absorption spectroscopic (XAS)
studies on the insulating barrier STO sandwiched byLSMO layers.
Experimental
The LSMO/STO/LSMO junctions were fabricated in alaser MBE chamber connected to a synchrotron radiation
photoemission system at BL-2C of the Photon Factrory[3]. A Nd:YAG laser was used for ablation in its
frequency-tripled mode (λ= 355 nm) at a repetition rate of
1 Hz. During deposition, the substrate temperature was-4
kept at 1050 °C and the oxygen pressure was 1 x 10 Torr.
After cooling down below 100 ºC, the multilayers weretransferred into the photoemission chamber under the-10
vacuum of 10 Torr. The PES spectra were taken withtotal energy resolution of about 150 meV. The XAS
spectra were obtained by measuring the sample draincurrent.
Results and Discussion
Figure 1 shows the Ti 2p core level spectra of theLSMO/STO/LSMO junction. The elemental selectivity ofthe techniques enables us to extract the electronicstructure (valency) of the STO layer. We have found that4+
Ti 2p core-level spectra clearly show Ti states and do3+
not exhibit any indication of Ti states in TiO2 layers
irrespective of a different kind of adjacent atomic layer
with different chemical carrier concentration. This result

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indicates that the Ti ions in the TiO2 atomic layers
preserve their tetravalent states even in the vicinity of thevalence-mismatched interface between LSMO and STO,
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reflecting chemical stability of the Ti states.
References

Fig1: Ti 2p core-level spectra of STO layers withdifferent
layer
thicknesses
for
LSMO/STO/LSMO junctions.
[1] J. Z. Sun et al., Appl. Phys. Lett. 69, 3266 (1996).
[2] H. Yamada et al., Science 305, 647 (2004).
[3] K. Horiba et al., Rev. Sci. Instrum, 74, 3406 (2003).
* kumigashira@sr.t.u-tokyo.ac.jp