Photon Factory Activity Report 2004 #22 Part B (2005)
Surface and Interface

2C/2002S2-002

In-situ synchrotron-radiation photoemission characterizationof SrTiO3/La0.6Sr0.4MnO3 heterointerfaces
H. Kumigashira1*, R. Hashimoto1, A. Chikamatsu1, M. Oshima1, T. Ohnishi2,
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3
3
4
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M. Lippmaa , H. Wadati , A. Fujimori , K. Ono , M. Kawasaki , and H. Koinuma
1

Department of Applied Chemistry, The Univ. of Tokyo, Tokyo 113-8656, Japan
Department of Physics and Department of Complexity Science and Engineering, The Univ. ofTokyo, Kashiwa 277-8561, Japan
3
Institute for Solid State Physics, The Univ. of Tokyo, Kashiwa 277-8581, Japan
4
Institute of Materials Structure Science, KEK, Tsukuba 305-0801, Japan
5
Institute for Materials Research, Tohoku Univ., Sendai 980-8577, Japan
6Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan
2Introduction
The half metallic nature of optimally hole-doped
manganese oxides makes the manganites intriguing forpotential applications in magnetroelectronic devices in
the form of heterostructures, such as tunnelingmagnetoresistance (TMR) devices.
However, theperformance of TMR devices is far below what is
expected from the high spin polarization, suggesting the“dead layer” formation at heterointerfaces [1,2]. In order
to investigate an interfacial electronic structure, we have
performed the Mn 2p-3d resonant photoemission (RPES),
core-level photoemission, and x-ray absorption
spectroscopic(XAS)
studyonSrTiO3(STO)/
La0.6Sr0.4MnO3(LSMO) multilayers.

STO layers. By contrast, Ti 2p core level spectra are4+
indicative of typical Ti states with octahedral crystal
4+
symmetry (not shown). The preservation of Ti states in
the STO capping layer may be due to the high chemical
stability of TiO2 plane in the STO. These results suggestthat the hole doped into the LSMO layer close to theheterointeface originates from the chemical carrierconcentration modulation at the valence-mismatchedinterface composed of the stacking sequence –TiO2–SrO–MnO2–La0.6Sr0.4–, which is proper to multilayers based on
perovskite oxides [2].

Experimental
The LSMO/STO multilayers 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 of1 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-10vacuum of 10 Torr. The PES spectra were taken withtotal energy resolution of about 150 meV at the photon
energy of 640 eV.
Results and Discussion
Figure1showstheMn2p-3dRPE
S spectra of STO/LSMO multilayers. The elemental
selectivity of these techniques enables us to extract the 3dpartial density of states of LSMO layer in the vicinity ofthe interface with the STO overlayers. We have foundthat the spectral intensity of Mn 3d eg↑ states near theFermi level is drastically reduced when the LSMO film iscapped with the STO overlayer, indicating the occurrenceof hole doping into Mn sites in LSMO layers close to70

Users' Report

Fig.1: Mn 2p-3d RPES spectra of STO/LSMOmultilyaers.
References[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