Suppressing the field-induced agglomeration in the magnetic fluid
by doping the nonmagnetic particles
Ziyun Di, Xianfeng Chen,
a͒
Jingfei Chen, and Yuxing Xia
Department of Physics, the State Key Laboratory on Fiber Optic Local Area Communication Networks
and Advanced Optical Communication Systems, Shanghai Jiao Tong University, Shanghai 200240, China
Shengli Pu
College of Science, University of Shanghai for Science and Technology, Shanghai 200093, China
͑Received 16 January 2007; accepted 25 March 2007; published online 20 April 2007͒
A method for suppressing the field-induced agglomeration of magnetic particles in a magnetic fluid
is proposed in this letter. After the magnetic fluid is doped with nonmagnetic silica particles, the
field-induced agglomeration effect is weakened, and this suppressing effect is expressed by the
measured birefringence magnitude and the simulation results of the agglomeration parameter. The
optical properties of this system such as the optical transmission and response time are analyzed.
With this method, the quality of the magnetic-fluid-based optical devices might be improved. ©
2007 American Institute of Physics. ͓DOI: 10.1063/1.2731442͔
Magnetic fluid ͑MF͒ which consists of single domain
magnetic particles dispersed in a nonmagnetic liquid solvent
has been studied for a long time. Its magneto-optical proper-
ties have recently attracted a lot of interest of many scientists
due to their potential applications.
1–6
It is indicated that the
birefringence effect is attributed to the formation of magnetic
chains under magnetic fields,
7–9
and our previous research
has established a quantitative relationship between the bire-
fringence and the chains formation.
10
On the other hand, the
optical transmission of MF under external fields is another
important area of magneto-optical effects.
11–13
The optical
transmission of MF can be modulated by varying the field
strength,
11,14
which implies that MF film can be used for
optical switches,
14
modulators,
15
etc. According to these re-
sults, the optical transmission is deeply related to the struc-
tural patterns of MF under external fields. Yang et al. have
proven that the magnetic-field-dependent optical transmis-
sion originates from the agglomeration of the magnetic par-
ticles that reduces the area of the liquid phase.
16
The larger
the fields, the more chains are formed, so the transmission is
inversely proportional to the fields. It is this agglomeration
process that plays an important role in the optical transmis-
sion, such as the response time of switches or
modulators.
17,18
Hence, in this letter, by taking account of
reducing the agglomeration formation, doped MFs are inves-
tigated, whose suppressing ability is expressed by the bire-
fringence effect by both the experimental and simulation re-
sults. Finally we discussed the feasibility of improving the
quality of the magnetic-fluid-based optical devices by the
utilization of this system.
The samples we used here were water-based Fe
3
O
4
MFs
doped with the silica particles, and the mixture was under
sonication for hours by using the steric way of
stabilization.
19
In our experiment, the water-based Fe
3
O
4
MFs are provided by Jinke Magnetic Fluids Co. Ltd, and the
silica particles are provided by Research Centre of Micro/
Nano Science and Technology of Shanghai Jiao Tong Uni-
versity. The average diameters of the silica particles and
magnetic particles of the MFs are both 10 nm. ͑It is worth
mentioning that if the diameters of nonmagnetic particles are
much larger than the MFs’, then it is another situation.
20
͒ In
order to well investigate the agglomeration effect, samples
with different concentrations were prepared: 3% of MFs
doped with 1 % /2% of silica particles and 9% of MFs doped
with 1% /2% of silica particles, and all the fraction here is
the volume fraction. The fluid was then injected into a
7-
m-thick glass cell to form a film. The experimental setup
for measuring the birefringence effect used here is schemati-
cally illustrated in Fig. 1. A 1.447 mW single mode He–Ne
laser with a wavelength of 632.8 nm is employed. The
propagation direction of the light is nomal to the applied
magnetic field. At a given magnetic field for a given sample,
the transmittance of light was investigated by rotating the
analyzer and determining the maximum and minimum trans-
mitted intensities I
max
and I
min
, respectively. The value of
birefringence ⌬n is determined to be
21
⌬n = sin
−1
2
ͱ
I
min
/I
max
ch͑h
1
− h
2
͒
1+I
min
/I
max
/͑2
d͒,
where d is equal to 7
m, is 632.8 nm, and h
i
͑i =1,2͒ is
the absorption coefficient along two directions which can be
obtained by solving the equation I
i
=I
0i
e
−2h
i
͑H͒
͑I
0i
is the in-
tensity of the output in zero field͒.
a͒
Electronic mail: xfchen@sjtu.edu.cn FIG. 1. Schematic diagram of the experimental setup.
APPLIED PHYSICS LETTERS 90, 161129 ͑2007͒
0003-6951/2007/90͑16͒/161129/3/$23.00 © 2007 American Institute of Physics90, 161129-1