DOI: 10.1007/s00339-006-3766-y
Appl. Phys. A 86, 261–264 (2007)
Materials Science & Processing
Applied Physics A
j. wan
1,2,✉
g. tang
1
y. qian
2
Room temperature synthesis
of single-crystal Fe
3
O
4
nanoparticles
with superparamagnetic property
1
Institute of Advanced Materials, Graduate School of Shenzhen, Tsinghua University, Shenzhen,
Guangdong 518055, P.R. China
2
Hefei National Laboratory for Physical Sciences at Microscale and Department of Chemistry,
University of Science and Technology of China, Hefei, Anhui 230026, P.R. China
Received: 15 May 2006/Accepted: 16 October 2006
Published online: 22 November 2006 • © Springer-Verlag 2006
ABSTRACT
Single-crystal Fe
3
O
4
nanoparticles with uniform
size and relatively better monodispersity have been successfully
synthesized via a facile room temperature coprecipitation route
in the present of poly(vinyl pyrrolidone) (PVP). This method
does not require high temperature, expensive and toxic starting
materials, complicated procedure and toxic organic solvents.
The magnetic properties of as-prepared samples were recorded
on a superconducting quantum interference device magnetome-
ter. Its blocking temperature is 140 K. The hysteresis loops of
single-crystal Fe
3
O
4
nanoparticles at 300 K and 10 K show the
transition from superparamagnetic to ferromagnetic behavior.
And the maintenance of high saturation magnetization ascribes
to the single-crystalline nature of these Fe
3
O
4
nanoparticles.
PACS
75.50.K; 75.70.C
1 Introduction
The synthesis of nanoparticles with controlled size
and composition is of fundamental and technological interest.
Due to their extremely small dimensions, these nanoparticles
often exhibit novel electronic, optical, magnetic and chem-
ical properties [1–3]. The effort to understand the physics of
nanoparticles has been paralleled by attempts to exploit their
beneficial properties [4, 5]. Magnetite (
Fe
3
O
4
) is a common
magnetic iron oxide that has a cubic inverse spinel struc-
ture [6]. Owing to its structure, magnetite had been widely
used in many important technological applications, such as
information storage, electronic devices, ferrofluids, refriger-
ation, biomedical imaging, medical diagnostics and drug de-
livery [7–10]. It is important for all these applications to syn-
thesize superparamagnetic nanoparticles with diameter less
than
15 nm
and a narrow size distribution. However, to syn-
thesize magnetite particles with small sizes and an accept-
able size distributionwithoutparticles aggregationhas consis-
tently been a challenge.
In nanoparticle dispersions, it is important that each par-
ticle is stabilized against aggregation with a layer of organic
or inorganic coating. For
Fe
3
O
4
nanoparticles, it is especially
✉ Fax: +86-551-26036752, E-mail: wanjx@mail.sz.tsinghua.edu.cn
difficulty to obtain relatively better monodispersity due to
its inherent magnetism. Therefore, surfactant
/
organic coat-
ing are necessary for the synthesis of monodispers
Fe
3
O
4
nanoparticles [11–13]. The physical and chemical proper-
ties of magnetite nanoparticles are greatly affected by the
synthesis route and for this reason various approaches, such
as high-temperature organic phase decomposition of an iron
precursor [14, 15], hydrothermal route [16], electrochemical
route [17], DC thermal arc-plasma route [18], microemulsion
route [19] and solvothermal route [20], have been employed
to produce magnetite with expected properties. Many of these
methods need high temperature, expensive and toxic starting
materials, complicated procedure and toxic organic solvents.
Herein, we chose inexpensive and nontoxic starting materi-
als and synthesized single-crystal
Fe
3
O
4
nanoparticles with
relatively better monodispersity via a facile room temperature
coprecipitation route in the present of PVP, which is similar to
our previous work [21].
2 Experimental
All reagents were purchased from Shanghai Chem-
ical Reagent Co. and used without further purification. In
a typical procedure,
0.2g
PVP (K30) and
2.0 mmol FeCl
3
were dissolved in
30 ml
distilled water in a conical flask
of
50 ml
capacity at room temperature. Then about
5ml
toluene was layed above the aqueous solution and
1.0 mmol
FeSO
4
·
7H
2
O was added into the solution. Herein, toluene was
used just as oil membrane covered over the mixed aqueous
solution of ferrous and ferric ions to separate the ferrous ion
from oxygen. Reactants were dissolved in distilled water and
the reaction was carried out in distilled water. After about
10 minutes
, the aqueous solution of
1g
NaOH dissolved in
5ml
distilled water was added under stirring. The mixture be-
came black immediately. The conical flask was sealed, and
maintained at room temperature (about
20
◦
C
)for
12 h
.The
resulting black solid products were collected by centrifuga-
tion at about
15 000 rpm
for several minutes and washed with
distilled water and absolute ethanol for several times, respec-
tively, and finally dried in vacuum at
60
◦
C
for
4h
.
The phase purity and phase structure of as-prepared sam-
ples were characterized by the X-ray powder diffraction
(XRD) pattern, using a Philips X’pert X-ray diffractome-
ter equipped with graphite monochromatized
Cu K
α
radia-