Photon Factory Activity Report 2016 #34 (2017)

BL-27B/2015G516

Microstructure of implanted Fe nanoparticles in silica glassand their effect on magnetic properties
Kengo Fukuda1 Masaaki Ochi1, Hiroshi Kojima1, Ren Mayumi1, Yoshihiro Okamoto2,
Satoshi Semboshi3, Yuichi Saitoh4, Fuminobu Hori1 and Akihiro Iwase1,*,1Department of Materials Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
Materials Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan
3
Institute for Materials Research, Tohoku University, Sakai, Osaka, 599-8531, Japan4National Institutes for Quantum and Radiological Science and Technology, Takasaki, Gunma, 3701292, Japan

2

1 Introduction
Nanocomposite glasses containing metal nanoparticles
in matrix have become an object of interest among many
researchers because of their promising properties. For
example, they can provide new magnetic, optical or
dielectric properties and so on. Among them, we focus onmagnetic properties. The distribution of metal
nanoparticles (Fe, Co, Ni) will lead to the modification of
the magnetic properties [1]. There are several well-known
methods to prepare metal nanoparticles in solids. Ion
implantation is one of the most suitable techniques for thesynthesis of metal nanoparticles in solid host matrix. Also,
by subsequent heavy ion irradiation, the magnetic
property and the state of implanted ions may be changed.
In order to understand the oxidation state of implanted
elements, the x-ray absorption near edge structure(XANES) is a good tool.
In the present study, we have investigated the effect of
Fe ion implantation and the subsequent energetic heavy
ion irradiation on the magnetic properties andmicrostructure of Fe clusters in silica glass by SQUID,
TEM and XANES measurements.
2 Experiment
Target samples were amorphous SiO2 sheets with thedimension of 5mmx5mmx1mm. They were implantedwith 380keV Fe ions at various fluences at room
temperature by using an ion-implanter at Takasaki
Advanced Radiation Research Institute, QST. After theion implantation, some samples were subsequently
irradiated with 16MeV Au ions. The effects of theimplantation and the subsequent high-energy ion
irradiation on magnetic properties were studied by using aSQUID magnetometer. Microstructures of implanted Fe
nanoparticles were observed by transmission electron
microscope (TEM). In order to investigate the oxidation
state of the implanted Fe ions, the x-ray absorption nearedge structure (XANES) was measured at a synchrotron
radiation facility of High Energy Accelerator ResearchOrganization (KEK-PF).
3 Results and Discussion
In Fig.1, Fe K-edge XANES spectra for some modelcompounds (Fe, FeO, Fe2O3) are shown. Depending on

the Fe oxidation state, the XANES spectra varysystematically in the position of the pre-edge peaks(7.11~7.12keV). The peak position shifts to low energies
with decreasing the valence number of Fe ion. From thisresult, pre-edge peaks for the Fe implanted samples help
us estimate Fe oxidation state in SiO2.
In Fig.2, Fe K-edge XANES spectra for Fe-implanted
silica glass are shown. From this figure, pre-edge peak
position shifts to low energies with increasing the amountof implanted Fe ions. This result suggests that the valence
number of implanted Fe ions decreases and becomesclose to zero (pure Fe) if Fe ion fulence becomes larger.
In other words, when focused on one Fe atom implanted
in silica glass, more Fe atoms exist around the Fe atomwith increasing ion fluence.
In Fig.3, the transmission electron microscope (TEM)
images of Fe implanted silica glass are shown. The left
figure is for Fe ion fluence of 1.4×1017 (/cm2). The rightone is for 7×1016 (/cm2). These TEM images show that
depending on Fe ion fluence, the size of Fe nanoparticles
is different. With increasing the amount of implanted Fe
ions, the size of Fe nanoparticles becomes larger.
In Fig.4, the magnetization for the silica glassimplanted with Fe ions at 300K as a function of magnetic
field is shown. The experimental result shows that themagnetic state of implanted Fe is the ferromagnetism or
the super-paramagnetism. Also, the magnetization for one
Fe atom implanted in silica glass increases withincreasing the amount of implanted Fe ions. From theexperimental results of the XANES measurement and theTEM observation (Fig.1, Fig.2), clusters produced fromthe implanted Fe ions become close to metallic Fe
clusters, and their size becomes larger with increasing theamount of implanted Fe ions. This is the reason why themagnetization per one Fe atom increases with increasing
the amount of implanted Fe atoms.
In Fig.5, the magnetization for Fe-implanted silica
glass before and after the Au ion irradiation is shown. By
the subsequent 16MeV Au ion irradiation, the value ofmagnetization a little decreases. To understand thischange by the subsequent Au ion irradiation, XANES
measurement and TEM observation will also be useful.

Photon Factory Activity Report 2016 #34 (2017)

Acknowledgement
The authors thank the staff of QST-Takasakiaccelerator facility for their help. The present study has
been carried out under the collaborations between Osaka
Prefecture University and QST-Takasaki.
References[1] Y. Fujimura et al., J. Alloy. Com. 682 (2016) 805-814

Fig.3 TEM images of Fe nanoparticles implanted insilica glass

Fig.1 XANES spectra near Fe K-edge for pure Fe, FeO,and Fe2O3

Fig.4 Magnetization for silica glass implanted with Feions at 300K as a function of magnetic field.

Fig.2 XANES spectra near Fe K-edge for Fe-implanted
SiO2 samples
Fig.5 Magnetization for silica glass implanted with Fe
ions before and after Au ion irradiation.

* iwase@mtr.osakafu-u.ac.jp