Photon Factory Activity Report 2005 #23 Part B (2006)
Materials Science

NE1B/2005G001

Fe L2,3 MCD spectra from Fe/Si multilayers
Masaki SUGAWARA, Kosuke SATO, Tadashi HATANO, Mitsunori TOYODAand Mihiro YANAGIHARA*
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University
2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan

Results
Figure 1(a) shows Fe L2,3 absorption spectra measured
using photocurrent from an Fe/Si(1.3nm) multilayer for
two circular polarization modes at an oblique angle of 15°.
An MCD spectrum obtained from Fig. 1(a) is shown inFig. 1(b). Spin and orbital magnetic moments calculated
from the obtained spectra using the sum rules are plotted
as a function of Si layer thickness of the samples in Fig. 2,
where solid and open circles stand for the moments of thesamples with the topmost Fe layer of 1.0 nm and 2.0 nm
thick, respectively. Our moments are small as comparedwith those of the bulk, which may come from oxidationof the surface Fe layer. It is remarkable in Fig. 2 that thespin moment is enhanced for the sample of 1.3-nm Si7

Fe L 2,3 Si=1.3nm 15 °6XAS(µ+)XAS(µ−)MCD× 2Absorption

54(a)3210-1MCDExperimental
Fe(3.0nm)/Si(t) (t = 0.5, 1.3, 1.7, 2.0 nm) multilayers
were prepared on Si wafers using a magnetron sputter
system. The topmost Fe layer was designed as thin as 1.0or 2.0 nm due to the escape depth of the photoelectrons. Itwas confirmed that the sample of 1.3-nm thick Si layer
was antiferromagnetic, while those of 0.5 and 1.7 nm
thick were ferromagnetic. The MCD experiment was
carried out at AR-NE1B using an absorption MCXD
apparatus equipped with a permanent magnet unit ofabout 1.0 T. Prior to the experiments sample holder andits attachment were thoroughly renewed because the soft
X-ray beam should be incident at oblique angles to meetthe in-plane magnetization in Fe/Si multilayers.

layer rather than those of 0.5 and 1.7-nm Si layer. It
seems contradictory that the antiferromagnetic sample has
a little bit enhanced moment. However, taking account of
the escape depth of photoelectrons, it could be interpreted
that the spin moment of the topmost Fe layer and therelated interdiffused layer is enhanced for the
antiferromagnetically-coupled Fe/Si multilayer rather
than for the ferromagnetically-coupled ones. This result
should be confirmed for oxidation-free samples.

(b)

-2-3

690

700

710

720

730740

Photon energy (eV)Fig. 1. (a) Fe L2,3 absorption spectra of an Fe/Si(1.3nm)
multilayer for two polarization modes and (b) an MCD
spectrum obtained from (a).

1.0
Spin
Magnetic moment (µ B )Introduction
Fe/Si multilayers are widely studied from the aspect ofthe strong antiferromagnetic interlayer coupling. We havefound for antiferromagnetically-coupled Fe/Si multilayers
using soft-X-ray fluorescence (SXF) spectroscopy that noSi layer remains at all during the interdiffusion and thatan amorphous (a-) FeSi2 layer of 0.7 nm thick issandwiched with a-Fe3Si layers [1]. We have thus
assigned the mediating layer for the interlayer coupling tobe the a-FeSi2 layer. It is quite interesting that the Fe/Si
multilayer exhibits strong interlayer coupling regardlessof the interdiffused layer of about 1 nm thick. Magnetic
state of the interdiffused layer should be investigated asthe next step. To examine the buried layers in multilayers
magnetically, X-ray magnetic circular dichroism (MCD)
combined with soft-X-ray standing waves might be auseful tool. In this study, we measured MCD spectra at
the Fe L2,3 thresholds and obtained a preliminary result
using the escape depth of photoelectrons.

0.80.6
Topmost Fe 1.0nm
2.0nm

0.40.2
Orbital
0.0
0.5

1.0
1.5
Si layer (nm)2.0Fig. 2. Spin and orbital moments plotted as a function ofSi layer thickness.
References[1] T. Imazono et al., Jpn. J. Appl. Phys. 43, 4327 (2004).
* m.yanagi@tagen.tohoku.ac.jp

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