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

2C/2005G101, 2005S2-002

Soft x-ray linear dichroism study of La1−xSrxMnO3 epitaxial thin films
Hiroki WADATI*1, Atsushi MANIWA2, Hiroshi KUMIGASHIRA2, Atsushi FUJIMORI1,Masaharu OSHIMA2, Mikk LIPPMAA3, Masashi KAWASAKI4, Hideomi KOINUMA5
1
Department of Physics and Department of Complexity Science and Engineering,
University of Tokyo, Kashiwa 277-8561, Japan2
Department of Applied Chemistry, University of Tokyo, Tokyo 113-8656, Japan
3
Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan
4
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
5
National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
Introduction
Hole-doped perovskite manganese oxides R1-xAxMnO3,
where R is a rare-earth (R = La, Nd, Pr) and A is analkaline-earth atom (A = Sr, Ba, Ca), have attracted muchattention because of their remarkable physical properties,
such as colossal magnetoresistance, and ordering of spin,
charge, and orbitals [1]. It was reported that the magneticand electronic phases can be controlled for thin films ofLa1-xSrxMnO3 grown on perovskite substrates withvarious lattice parameters [2]. Recently, Huang et al. [3]succeeded in observing the orbital states of the bulk
samples of La1-xSr1+xMnO4 by measuring the linear
dichroism (LD) in the Mn 2p x-ray absorption spectra. In
this study, in order to observe the orbital states, we have
performed in-situ x-ray absorption spectroscopy (XAS)
measurements of epitaxial thin films of La0.6Sr0.4MnO3grown on LaAlO3 (001) (under compressive strain) andSrTiO3 (001) (under tensile strain) substrates by laser
molecular beam epitaxy (laser MBE).

mainly in d3z2 - r2 (out-of-plane) orbitals. This can be easily
explained by the compressive strain from LaAlO3 (001)substrates, which is expected to split the energy levels ofeg orbitals and stabilize the out-of-plane orbitals. Theseresults are consistent with the phase diagram proposed by
Konishi et al. [2]. Figure 1 (b) shows the result of a La1xSrxMnO3 epitaxial thin film grown on SrTiO3 (001)substrates. The LD signal was expected to be negligible
due to the isotropy of orbitals in the ferromagnetic state.
However, the experimental LD was very similar to thecase of LaAlO3 (001). This LD signal was unexpected,and further experimental and theoretical studies areneeded to resolve this issue.
We are now constructing a new experimental setup for
LD measurements which can eliminate experimental
artifacts related to the difference in the optical path and to
the probing area [5].
La0.6Sr0.4MnO3/LaAlO3(b)(a)

Results and Discussion
Figure 1 (a) shows the polarization-dependent XAS
and LD spectra of a La1-xSrxMnO3 epitaxial thin filmgrown on LaAlO3 (001) substrates. The line shape of LD
was very similar to that of LaSrMnO4 reported by Huang
22et al. [3]. LaSrMnO4 is expected to exhibit 3z - r ‘‘ferroorbital’’ ordering, and Huang et al. succeeded inreproducing the LD spectrum of this material by multiplet
3+
calculations for Mn ions with occupied d3z2 - r2 orbitals.
4+
Since the LD signal from Mn sites is considered to be
negligible, the present result indicated that the eg electrons
in a La0.6Sr0.4MnO3 thin film grown on LaAlO3 (001) were

T = R. T.
E|cE // c
LD = ( | - //)Intensity (arb. units)

E|cE // c
LD = ( | - //)Intensity (arb. units)Experimental
The La0.6Sr0.4MnO3 thin films were fabricated in a laser
MBE chamber connected to a synchrotron radiation
photoemission system at BL-2C of the Photon Factory [4].
La0.6Sr0.4MnO3 thin films were deposited on LaAlO3 (001)osubstrates at 500 C and on SrTiO3 (001) substrates ato-41050 C at an oxygen pressure of 1 × 10 Torr. The
fabricated La0.6Sr0.4MnO3 thin films were transferred into-10
the photoemission chamber under vacuum of 10 Torr.
The XAS spectra were taken at room temperature in the
total-electron-mode.

La0.6Sr0.4MnO3/SrTiO3
T = R. T.

640

650660670

640

Photon Energy (eV)

650660670

Photon Energy (eV)Fig. 1: Polarization-dependent XAS and LD spectraof La0.6Sr0.4MnO3 epitaxial thin films grown on (a)LaAlO3 (001) and (b) SrTiO3 (001) substrates.
References[1] Y. Tokura and N. Nagaosa, Science 288, 462 (2000).
[2] Y. Konishi et al., J. Phys. Soc. Jpn. 68, 3790 (1999).
[3] D. J. Huang et al., Phys. Rev. Lett. 92, 087202 (2004).
[4] K. Horiba et al., Rev. Sci. Instr. 74, 3406 (2003).
[5] W. B. Wu et al., J. Electron Spectrosc. Relat. Phenom.
137–140, 641 (2004).
*wadati@wyvern.phys.s.u-tokyo.ac.jp

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