Journal of Alloys and Compounds 408–412 (2006) 203–206
The first observation of the magnetic circular dichroism
in EuS nanocrystals
a
a
a
Yasunori Tsukahara , Tomoharu Kataoka , Yasuchika Hasegawa ,
b
∗
Sumio Kaizaki , Yuji Wada
a
Material of Life Science, Graduate School of Engineering, Osaka University, Yamadaoka Suita, Osaka 565-0871, Japan
b
Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
Available online 20 June 2005
Abstract
EuS nanocrystals were prepared by the liquid ammonia method. The size effect of EuS nanocrystals was observed in the magnetic
measurements, the absorption spectra and the MCD spectra.
©
2005 Elsevier B.V. All rights reserved.
Keywords: Nanostructure; Semiconductor; Magnetic measurement
1
. Introduction
In this work, the spectroscopic and magnetic properties of
EuS nanocrystals have been examined systematically (size:
18, 29 and 36 nm). We report the characterization, the mag-
netic properties, the absorption spectra and the MCD analysis
of the EuS nanocrystals.
There has been significant interest in the ferromagnetism
of europium chalcogenides from the viewpoint of the ideal
Heisenberg model. The chalcogenides (EuO and EuS) have
4
f orbitals that exist as the degeneracy levels between the con-
duction band (5d orbitals of Eu(II)) and the valence band (2p
orbitals of O2 or 3p orbitals of S ) [1]. The spin moments
−
2−
2. Experiment
of Eu(II) ions come from the 4f electrons [2,3].
We reported the preparation of EuS nanocrystals (aver-
age size of 20–40 nm) by use of liquid ammonia [4]. It is
knownthatcrystalsizeaffectsopto-magneticproperties[5–7]
of europium chalcogenides. However, the size contribution
to the opto-magnetic properties has not been clear yet. We
propose that the spectral analysis of EuS nanocrystals in
magnetic field is directly connected to understanding of the
properties depending on their sizes.
Here, we have attempted to observe the absorption spec-
tra of EuS nanocrystals under magnetic field using magnetic
circular dichroism (MCD). MCD is a useful tool for infor-
mation on the excited states connected with the ground states
through the magnetic interactions [8].
2
.1. Materials
Europium metal (Eu 99.9%) was obtained from Sterm
Chemicals. Hydrogen sulfide (pure H2S) and ammonia
NH3 99.9%) were purchased from Sumitomo-seika and
Iwatani-neriki, respectively. The standard europium solution
1000 ppm) and sodium sulfate anhydrous (Na2SO4 99.0%)
(
(
werepurchasedfromWako. Allofthechemicalswerereagent
grade and were used as received.
2.2. Preparation of EuS nanocrystals
Europium metal (0.3 g) was added to liquid ammonia
◦
(
50 mL, −78 C) in a reaction flask. The color of the solution
∗
turned into deep blue with the dissolution of europium. H S
2
Corresponding author.
E-mail address: ywada@mls.eng.osaka-u.ac.jp (Y. Wada).
gas was introduced into the solution through bubbling until
0
925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2005.04.055