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

2C, 19B/2004G013

Soft X-ray fluorescence spectroscopy of FexCo1-xSi
Nobuo NAKAJIMA*1, Takahiro MAEDA2, Ki-Yong SEONG1, Naoki ISHIMATSU1,Yasuhisa TEZUKA2, Yoshiharu ENTA2 and Hiroshi MARUYAMA1
1Grad. Sch. of Sci., Hiroshima Univ., 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan
2Fac. of Sci. and Tech., Hirosaki Univ., 3 Bunkyo, Hirosaki 036-8561, JapanExperiment
SXF spectra were observed at BL-19B of KEK-PF. Themeasurements were carried out under room temperatureand ultrahigh vacuum of less than 3×10-7Pa. Si 2p SXF
spectra were recorded using a 300l/mm bent grating having a 5m radius with a 100µ -input-slit. FexCo1-xSi samples
were previously prepared by Watanabe et al. using aplasma-jet-flame furnace [2,3]. The samples were lessoxidized and quite stable. Owing to the advantage of thedepth probing power of SXF utilizing synchrotron radiation as an excitation light, no sample cleaning procedurein the chamber was required.
Results and Discussion
Figure 1 shows the Si 2p SXF spectra measured forFexCo1-xSi alloys of x = 0.07, 0.42, 0.61 and 1. Incident
photon energy was 131eV. Two broad peaks labeled A andB are observed at emission energies of 90.5 eV and 94.8
eV for all samples. The relative intensity of the peak B
compare to the peak A is strongly enhanced with increasing Co concentration (1-x). The electronic characters ofthese two peaks are essentially the same as those of thepeaks observed in SXF spectra of amorphous Fe1-xSix [4].
Imazono et al., have associated the main peak, which corresponds to the peak A in Fig.1, with non-bonding Si 3s
orbital and the shoulder feature, which corresponds to thepeak B in Fig.1, with Fe 3d orbital. In our case, the peakB is associated with transition-metal 3d orbital. The lattice constant of FeSi is larger than that of CoSi by one
percent [3] and also 3d electron number of FeSi is fewer

102

Users' Report

FexCo1-xSi
ASi 2phν = 131eV
B

Intensity (arb. units)

Introduction
Owing to the recent progress of evaporation technology,
a novel growth mode of Al on Si(111) has been reported[1]; with a slight Al deposition, sub-monolayer or a few,
well-ordered triangle islands were formed, which prevent
subsequent Fe deposits from forming a silicide. In orderto understand how the formation is prevented, first we
tackle another extreme, i.e., silicide itself.
The pseudobinary alloys of FexCo1-xSi (Fe-Co silicide)
exhibit weak itinerant ferromagnetism above a certain
critical field in the concentration range of 0.2<x<0.95[2],and with increasing Co concentration (1-x), the alloys
have a more itinerant character [3]. Indeed, FeSi (x=0) is
an insulator, whereas most of FexCo1-xSi alloys are metal.
In this report, we show the Si 2p soft X-ray fluorescence (SXF) spectra of these alloys and discuss about theinfluence of the itinerant character on the SXF spectra.

x=

1

10.6
20.4
70.0
85

9095100

Emission Energy (eV)Fig. 1 Si 2p SXF spectra of FexCo1-xSi (x = 0.07, 0.42,0.61, and 1). The vertical lines A and B are guides to theeye.
by one than that of CoSi, therefore the overlap of 3d orbitals onto the Si sites is reduced and the s-orbital peak A
becomes narrow. Namely, with substituting Fe with Co,
the numbers of 3d electrons gradually increase and the alloys become more itinerant. As a result, the intensity ofthe peak B increases.
Summary
The Si 2p SXF spectra of several FexCo1-xSi alloys
were measured. The x-dependence of characteristic peaks
were observed, which were interpreted within the framework of an itinerant-electron system.
References[1] H. Lie, et al., Surf. Sci., 571, 5 (2004); J. –F. Jia, et al.,Phys. Rev. B66, 165412(2002)[2] H. Watanabe, et al., J. Phys. Soc. Jpn. 54, 3978(1985);
J. Beille, et al., J. Magn. Magn. Mater., 10, 265(1979)[3] K. Shimizu, et al., J. Phys. Soc. Jpn. 58, 1914(1989);
ibid., 59, 305(1990)[4] T. Imazono, et al., Jpn. J. Appl. Phys., 43, 4327(2004);
ibid., 43, 4334(2004)* nobuo@hiroshima-u.ac.jp