Photo-induced electric polarizability of Fe3O4 nanoparticles in weak optical fields

Article (PDF Available)inNanoscale Research Letters 8(1):317 · July 2013with55 Reads
DOI: 10.1186/1556-276X-8-317 · Source: PubMed
Abstract
Using a developed co-precipitation method, we synthesized spherical Fe3O4 nanoparticles with a wide nonlinear absorption band of visible radiation. Optical properties of the synthesized nanoparticles dispersed in an optically transparent copolymer of methyl methacrylate with styrene were studied by optical spectroscopy and z-scan techniques. We found that the electric polarizability of Fe3O4 nanoparticles is altered by low-intensity visible radiation (I ≤ 0.2 kW/cm2; λ = 442 and 561 nm) and reaches a value of 107 Å3. The change in polarizability is induced by the intraband phototransition of charge carriers. This optical effect may be employed to improve the drug uptake properties of Fe3O4 nanoparticles. PACS 33.15.Kr 78.67.Bf 42.70.Nq
N AN O C O M M E N T A R Y Open Access
Photo-induced electric polarizability of Fe
3
O
4
nanoparticles in weak optical fields
Valentin A Milichko
1,2*
, Anton I Nechaev
3
, Viktor A Valtsifer
3
, Vladimir N Strelnikov
3
, Yurii N Kulchin
1
and Vladimir P Dzyuba
1
Abstract
Using a developed co-precipitation method, we synthesized spherical Fe
3
O
4
nanoparticles with a wide nonlinear
absorption band of visible radiation. Optical properties of the synthesized nanoparticles dispersed in an optically
transparent copolymer of methy l methacrylate with styrene were studied by optical spectroscopy and z-scan
techniques. We found that the electric polarizability of Fe
3
O
4
nanoparticles is altered by low-intensity visible
radiation (I 0.2 kW/cm
2
; λ = 442 and 561 nm) and reaches a value of 10
7
Å
3
. The change in polarizability is
induced by the intraband phototransition of charge carriers. This optical effect may be employed to improve the
drug uptake properties of Fe
3
O
4
nanoparticles.
Keywords: Magnetite nanoparticles; Electric polarizability; Low-intensity visible radiation
PACS: 33.15.Kr; 78.67.Bf; 42.70.Nq
Background
Magnetite (FeO*Fe
2
O
3
,orFe
3
O
4
) nanoparticles, and ma-
terials based on them, have been successfully used to
solve applied problems in biology and magneto-optics.
Pronounced superparamagnetic [1-4] and ferromagnetic
[5] properties at room temperature enable the use of
these nanoparticles in magnetic res onance imaging [6-9]
and biosensing [9] as well as in drug delivery and
drug uptake applications [8-13]. Because they possess
magneto-optical properties [14,15], Fe
3
O
4
nanoparticles
have also been used to develop tunable filters [16,17]
and optical switches [18,19] that operate under magnetic
fields.
In fa ct, Fe
3
O
4
nanoparticles have been examined for
the presence of unique magnetic prope rties because
magnetite is a narrow-gap semiconductor [20-22] and
the optical properties of other semiconductor nano-
particles have been thoroughly studied. Currently, there
are several experimental and theoretical works dedicated
to studying the optical properties of both bulk magnetite
[23-26] and its nanoparticles [27- 29]. However, some
specific optical properties of Fe
3
O
4
nanoparticles (in
particular, the effects of electric polarizability on their
biological activity, conductivity, ferroelectricity, and
electro-optical properties) as well as the nature of these
properties remain virtually unexplored.
In this paper, we demonstrate that Fe
3
O
4
nanoparticles
exhibiting a wide nonlinear absor ption band of visible
radiation (1.7:3.7 eV) are able to significantly change
their electric polarizability when exposed to low-
intensity visible radiation (I 0.2 kW/cm
2
). The ob-
served change in polarizability wa s induced by the
intraband phototransition of nanoparticle charge car-
riers, and polarizability changes were orders of magni-
tude greater than those of semiconductor nanoparticles
and molecules [30 ,31].
Experiments
Synthesis of nanoparticles
There are several techniques for the synthesis of Fe
3
O
4
nanoparticles with an arbitr ary shape and size and for
their dispersal in different matrices [4,5,11,12,27,29,32-36].
In this study, we synthesized nanoparticles using co-
precipitation method [1,2,13-15,37,38], dispersed them in
monomeric methyl methacrylate with styrene (MMAS),
and polymerized this composition using pre-polymerization
method.
* Correspondence: ariesval@mail.ru
1
Institute of Automation and Control Processes, FEB RAS, Radio 5, Vladivostok
690041, Russia
2
Far Eastern Federal University, Sukhanova 8, Vladivostok 690950, Russia
Full list of author information is available at the end of the article
© 2013 Milichko et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction
in any medium, provided the original work is properly cited.
Milichko et al. Nanoscale Research Letters 2013, 8:317
http://www.nanoscalereslett.com/content/8/1/317
In the first step (Figure 1a), Fe
3
O
4
nanoparticles were
synthesized by co-precipitation of soluble salts of ferrous
and ferric ions with an aqueous ammonia solution:
FeSO
4
*7H
2
O + 2FeCl
3
*6H
2
O + 8NH
3
*H
2
O Fe
3
O
4
+
6NH
4
Cl + (NH
4
)
2
SO
4
+ 20H
2
O.
Oleic acid (in a mass ratio of 0.7:1 with the formed
Fe
3
O
4
) was added to a 0.5% solution of iron salts
(FeSO
4
/FeCl
3
= 1:2.2 molar ratio) in 0.1 M HCl. The
aqueous solution of iron salts was heated to 80°C,
followed by the addition of concentrated aqueous am-
monia (20% excess). The solution was heated and stirred
for an hour.
Stabilized nanoparticles were then extracted from the
aqueous phase into a nonpolar organic solvent hexane at
a ratio of 1:1. The organic layer containing the iron
oxide Fe
3
O
4
was separated from the aqueous medium.
The sample was centrifuged for 15 min (6,000 rpm) to
remove larger particles. Excess acid was removed with
ethanol.
The size of the nanoparticles was determined by dy-
namic light scattering method (Zetasizer Nano Z S ,
Malvern, UK). Measurements were conducted in hexane
with a laser wavelength of 532 nm. The average hydro-
dynamic diameter of the synthesized nanoparticles was
15 nm, as illustrated in Figure 2.
Composite preparation
The second step (Figure 1b) focused on obtaining a solid
composite based on Fe
3
O
4
nanoparticles and MMAS.
The organic solvent containing nanoparticles and mono-
mers (methyl methacrylate with styrene) was subjected
to stirring and ultrasonic homogenization. To prevent
nanoparticle aggregation during the polymerization
process, we used the pre-polymerization method at 75°C
because the nanoparticles had different affinities to the
monomer and polymer.
Finally, the composite was synthesized in situ by radical
polymerization. The polymerization of methyl methacryl-
ate with styrene (in the mass ratio of 20:1) proceeded for
over 10 h (in a temperature gradient mode that progressed
from 55°C to 110°C) in the presence of benzoyl peroxide
(10
3
mol/L).
The obtained solid composites had 0.001%, 0.003%,
0.005%, and 0.01% volume concentrations of Fe
3
O
4
nanoparticles in MMAS. Importantly, the synthesized
Fe
3
O
4
nanoparticles generally had a thick layer of
acids [36,39] surrounding them to prevent aggregation
of the nanoparticle. In our case, the synthesized Fe
3
O
4
Figure 1 The developed co-precipitation method. (a) The synthesis of Fe
3
O
4
nanoparticles with a monolayer of oleic acid by the developed
co-precipitation method and (b) the composite MMAS + Fe
3
O
4
preparation.
Figure 2 Nanoparticle size. The average hydrodynamic diameter
of the synthesized nanoparticles (15 nm) dispersed in hexane was
determined by dynamic light scattering method (Zetasizer Nano ZS,
Malvern, UK) at a laser wavelength of 532 nm.
Milichko et al. Nanoscale Research Letters 2013, 8:317 Page 2 of 7
http://www.nanoscalereslett.com/content/8/1/317
nanoparticles had a monolayer of oleic acid that allowed
the nanoparticles to exhibit their specific optical properties.
UVvis spectroscopy
Room-temperature optical absorbance spectra of pure
MM AS (Figure 3, black curve) and of the composites
were obtained using a Varian Cary 5000I spe ctropho-
tometer (Agilent Technologies, Santa Clara, CA, USA)
over the wavelength range of 300 to 1,500 nm. These
spectra allowed the derivation of the absorbance spectra
for Fe
3
O
4
nanoparticle arrays (Figure 3, color curves).
Figure 3 shows the absorbance values (Abs) an d the ab-
sorption coefficients (α =(Abs×ln10)/l,wherel =7.95mm
is the length of the composite) measured at a maximum
radiation intensity of 1 μW/cm
2
.
z-Scan experiments
Because they have absorption bands of 380 to 650 nm,
Fe
3
O
4
nanoparticles should exhibit an optical response
upon external radiation with wavelengths in this band
[40]. To detect the optical response of the nanoparticles
contained in the composite (0.005% nanoparticle volume
concentration), we used the standard z-scan technique
[41]. This technique enabled the analysis of changes in
the absorption coefficient Δα(I) and refractive index Δn(I)
of the composite and pure MMAS, which were induced
by weak optical radiation with different intensities 0 to
0.14 kW/cm
2
.
For radiation sources, we used semiconductor lasers
of continuous wave (cw) radiation with wavelengths of
442 nm (blue) and 561 nm (yellow) providing maximal
intensities of 0.07 and 0.14 kW/cm
2
.Lenseswithfocal
lengths of 75 mm provided the beam waists ω
0
=102
and 110 μm for blue and yellow radiation (Figure 4b).
The length (L) of experimental samples of the MMAS
and the composite was 2.7 mm (inset in Figure 3).
Because the Rayleigh range z
0
= πnω
2
/ λ exceeded 10 cm,
the calculation of Δα and Δn was performed using the for-
mulae [40,41]:
Δα IðÞ¼
2
ffiffi
2
p
ΔΤ IðÞ
L
;
ΔnIðÞ¼γI ¼
λΔΤ
pv
IðÞα þ Δα IðÞðÞ
0:812π 1SðÞ
0:27
1e
αþΔα IðÞðÞL
ðÞ
;
8
>
>
<
>
>
:
ð1Þ
where ΔT(I) (Figure 4a) and ΔT
pv
(I) (Figure 5b) were the
integral transmitted intensity and the normalized
Figure 3 Absorbance spectra for the MMAS and Fe
3
O
4
nanoparticle array. The optical absorbance spectra for pure MMAS and Fe
3
O
4
nanoparticle arrays with 0.001%, 0.003%, 0.005%, and 0.01% volume concentrations.
Figure 4 z-Scan results for the MMAS. (a) Curves for z-scans with
open (circle) T(I) and closed (square) T
pv
(I) apertures at radiation
wavelengths of 442 nm (red points, 60 W/cm
2
) and 561 nm (blue
points, 133 W/cm
2
) for the MMAS sample (L = 2.7 mm). (b) Profilometer
images for the beam waists ω
0
.
Milichko et al. Nanoscale Research Letters 2013, 8:317 Page 3 of 7
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transmittance between the peak and valley at different ra-
diation intensities, respectively; λ and α were the radiation
wavelength and absorption coefficient (Figure 3), respect-
ively, and S was the fraction of radiation transmitted by
the aperture without the sample, which was 0.184.
The experimental curves T (I) and T
pv
(I), which con-
tain information about ΔT and ΔT
pv
, showed that only
the reverse saturable absorption of yellow radiation oc-
curred in pure MMAS (Figure 4a). In contrast, the com-
posite manifested the expected optical response: the
shape of the experimental curves T(I) and T
pv
(I) indi-
cated the saturab le absorption of visible radiation in the
composite and a negative change in its refractive index
(Figure 5), and the values of ΔT(I) and ΔT
pv
(I) increased
linearly with increasing intensities of blue (Figure 5a)
and yellow (Figure 5b) radiation.
The approximation of T
pv
based on the theoretical
curves (solid lines in Figure 5) was performed using the
equation [42]:
T ¼ 1 þ
2 ρx
2
þ 2x3ρðÞ
x
2
þ 9ðÞx
2
þ 1ðÞ
ΔΦ ð2Þ
where the coupling factor ρ = Δα × λ /4π × Δn and the
phase shift due to nonlinear refraction ΔΦ =2π × Δn ×
L
eff
/ λ had the following values: ρ = 0.09 and ΔΦ =
0.23 and 0.5 for blue radiation with intensities of
0.019 and 0.054 kW/cm
2
and ρ = 0.05 and ΔΦ = 0.7
and 1.45 for yellow radiation with intensities of 0.04
and 0.093 kW/cm
2
.
Discussion
The saturable absorption of visible radiation with inten-
sities less than 0.14 kW/cm
2
in the composite and the
negative change in the refractive index were due to the
presence of Fe
3
O
4
nanoparticles since pure MMAS
showed only the relatively weak reverse saturable ab-
sorption of yellow radiation. Therefore, the experimental
data ΔT(I) and ΔT
pv
(I) obtained for the composite could
be used to calculate the values of Δα (I) and Δn(I) for
Fe
3
O
4
nanoparticle arrays (Equation 1), and these values
are listed in Figure 6.
Because the observed dependence of Δn on the radi-
ation intensity I (Figure 6b) for Fe
3
O
4
nanoparticle ar-
rays could be considered a linear function, it can be
Figure 5 z-Scan results for the composite. Curves for z-scans with
open (circle) T(I) and closed (square) T
pv
(I) apertures at radiation
wavelengths of 442 nm (a) (red points, 19 W/cm
2
; blue points,
54 W/cm
2
) and 561 nm (b) (red points, 40 W/cm
2
; blue points,
93 W/cm
2
) for the composite sample (L = 2.7 mm) containing Fe
3
O
4
nanoparticle with a 0.005% volume concentration.
Figure 6 The values of changes in the absorption coefficient,
refractive index, and polarizability of Fe
3
O
4
nanoparticles.
(a) The dependency of changes in the absorption coefficients Δα of
pure MMAS (circle) and Fe
3
O
4
nanoparticle arrays (square and
rhombus) on the intensity of radiation with wavelengths of 442 nm
and 561 nm. (b) The dependency of changes in the refractive index
Δn and polarizability Δα
3
)ofFe
3
O
4
nanoparticle arrays on the
intensity of radiation with wavelengths of 442 nm (rhombus) and
561 nm (square); red dashed lines present the contribution of the
thermal effect of cw radiation on the change in the refractive index
(Equation 3), and blue dashed lines are theoretical approximations
based on the approach of free carrier absorption (Equation 4).
Milichko et al. Nanoscale Research Letters 2013, 8:317 Page 4 of 7
http://www.nanoscalereslett.com/content/8/1/317
assumed that Δn was caused by the thermal effect of the
radiation. We estimated the contribution of this effect to
the changes of the compos ite refractive index using the
equation [43]:
Δn
therm
¼
ΔΕ
dn
dT
c
hc
ρ
d
; ð3Þ
where c
hc
was the MMAS heat capacity (0.7 J/g·K), ρ
d
was the MMAS density (1.3 g/cm
3
), dn/dT was the
MM AS thermo-optic coefficient (10
5
K
1
), and ΔE
was the energy absorbed by the composite per unit vol-
ume per second. The thermal effect of cw low-intensity
radiation on the change in the refractive index (red
dashed lines in Figure 6b) was relatively small (not more
than 20% for blue radiation and 8% for yellow radiation).
Generally, the possibility of a nonthermal optical re-
sponse of the composite due to external optical radiation
is associated with the polarization of Fe
3
O
4
nano-
particles in the external field E. Nanoparticle polariza-
tion occurs at the spatial separation of positive and
negative charges, i.e., at the electron transition to higher
allowed energy states (quantum number l 0). These
transitions should be accompanied by the absorption of
external radiation. In our case, we observed the absorp-
tion of radiation with wavelengths of 380 to 650 nm
(Figure 3). This absorption band consisted of three max-
ima (380, 480, and 650 nm), indicating the broadened
quantum-size states for the electrons in Fe
3
O
4
nano-
particles. Because the bandgap of magnetite is rather
small (approximately 0.2 eV ) [20-22], the conduction
and valence bands of the nanoparticles should be
coupled due to quantum-size effect [44]. Therefore, the
transitions of Fe
3
O
4
nanoparticle electrons to higher en-
ergy states by the action of photons with energies of 2.3
eV (λ = 561 nm) and 2.6 eV (λ = 442 nm) can be consid-
ered intraband transitions. In turn, these transitions re-
sult in changes in the refractive index of the media as
follows [45-47]:
ΔnIðÞ¼
e
2
λ
2
8π
2
c
2
n
0
ε
0
m
e
N
e
ð4Þ
where e was the electron charge, c was the speed of light,
ε
0
was the electric constant, m
e
was the electron mass,
and N
e
was the concentration of excited electrons, which
depends on the number of photons in the beam or the
radiation intensity I.
Using Equation 4 to approximate the experimentally
observed behavior of Δn(I) (Figure 6b, blue dashed
lines), we estimated that the concentration of optically
excited electrons in Fe
3
O
4
nanoparticles was approxi-
mately 10
23
m
3
, being the radiation intensity of less
than 0.14 kW/cm
2
.
The amplitude of the nanoparticle polarization is deter-
mined by |E| of the external field and the nanoparticle
susceptibility (χ) or polarizability (α) measured in cubic
angstrom. In turn, the change in the refractive index in-
duced by the radiation is associated with the change in
nanoparticle polarizability Δα
3
) by classical relations
[48]. Therefore, we could calculate the values of Δα
3
)
for Fe
3
O
4
nanoparticle using the experimental values of
Δn(I) and the following equations (SI):
ε ¼ n
2
IðÞk
2
IðÞ¼1 þ χ
Δχ ¼ Δα Å
3
hi
10
30
Nm
3
½
(
ð5Þ
where ε was the real part of the dielectric constant, the
composite refractive index n(I)=n
0
+ Δn(I), and n
0
was
the refractive index of pure MMAS (approximately 1.5).
The extinction coefficient k = αλ /4π was significantly less
than n(I) and could be ignored; χ was the nanoparticle
susceptibility, and N was the nanoparticle concentration
(approximately 2.3 × 10
19
m
3
). Therefore, the values of
Δα
3
)forFe
3
O
4
nanoparticle were calculated using the
formula Δα
3
) 2n × Δn(I)×10
30
/ N and are presented
in Figure 6b.
The obtained values for the changes in nanoparticle
polarizability are orders of magnitude greater than those
for semiconductor nanoparticles and molecules [30,31]
in extremely weak optical fields. In addition, the average
nanoparticle volume was approximately 2.2 × 10
6
Å
3
,
and the maximum value of Δα
3
)was9×10
6
Å
3
.
Thus, we can conclude that the nanoparticle polarization
should be formed by several optical intraband transitions
of nanoparticle electrons in weak optical fields.
Conclusions
We used the developed co-precipitation method to
synthesize spherical Fe
3
O
4
nanoparticles covered with a
monolayer of oleic acid that possessed a wide nonlinear
absorption band of visible radiation 1.7 to 3.7 eV. The
synthesized nanopartic les were dispersed in the optically
transparent copolymer methyl methacrylate with styrene,
and their optical properties were studied by optical spe c-
troscopy and z-scan techniques. We report that the elec-
tric polarizability of Fe
3
O
4
nanoparticles changes due to
the effect of low-intensity visible radiation (I 0.2 kW/
cm
2
; λ = 442 and 561 nm) and reaches a relatively high
value of 10
7
Å
3
. The change in polarizability is induced
by the intraband phototransition of charge carriers and
can be controlled by the intensity of the visible radiation
used. This optical effect observed in magnetic nano-
particles may be employed to significantly improve the
drug uptake properties of Fe
3
O
4
nanoparticles.
Abbreviations
Abs: Absorbance; Cw: Continuous wave; MMAS: Methyl methacrylate with
styrene.
Milichko et al. Nanoscale Research Letters 2013, 8:317 Page 5 of 7
http://www.nanoscalereslett.com/content/8/1/317
Competing interests
The authors declare that they have no competing interests.
Authors contributions
VM designed and performed the optical experiments (z-scan and
spectroscopy), participated in the analysis and interpretation of data, and
prepared the draft and final version of the manuscript. AN, VV, and VS
designed and performed the chemical experiments, achieved that
nanoparticle was covered with a monolayer of oleic acid, prepared the
sections Synthesis of nanopartic le and Composite preparation. YK and VD
conceived of the study, participated in the analysis and interpretation of
data, helped to draft the final version of the manuscript. All the authors read
and approved the final manuscript.
Acknowledgments
The work was supported by the Programs of Presidium of Russian Academy
of Science (12-I-OFN-05, 12-I-P24-05, 12-II-UO-02-002) and by the Program of
UB RAS (12-S-Z-1004).
Author details
1
Institute of Automation and Control Processes, FEB RAS, Radio 5, Vladivostok
690041, Russia.
2
Far Eastern Federal University, Sukhanova 8, Vladivostok
690950, Russia.
3
Institute of Technical Chemistry, UB RAS, Academician
Korolyov 3, Perm 614013, Russia.
Received: 23 May 2013 Accepted: 1 July 2013
Published: 9 July 2013
References
1. Gass J, Poddar P, Almand J, Srinath S, Srikanth H: Superparamagnetic
polymer nanocomposites with uniform Fe
3
O
4
nanoparticle dispersions.
Adv Funct Mater 2006, 16:7175.
2. Wan J, Tang G, Qian Y: Room temperature synthesis of single-crystal
Fe
3
O
4
nanoparticles with superparamagnetic property. Appl Phys A 2007,
86:261264.
3. Mürbe J, Rechtenbach A, Töpfer J: Synthesis and physical characterization
of magnetite nanoparticles for biomedical application. Mater Chem Phys
2008, 110:426433.
4. Hashimoto H, Fujii T, Nakanishi M, Kusano Y, Ikeda Y, Takada J: Synthesis
and magnetic properties of magnetite-silicate nanocomposites derived
from iron oxide of bacterial origin. Mater Chem Phys 2012, 136:11561161.
5. Wang X, Zhao Z, Qu J, Wang Z, Qiu J: Fabrication and characterization of
magnetic Fe
3
O
4
-CNT composites. J Phys Chem Sol 2010, 71:673676.
6. Xie J, Chen K, Lee HY, Xu C, Hsu AR, Peng S, Chen X, Sun S: Ultrasmall c
(RGDyK)-coated Fe
3
O
4
nanoparticles and their specific targeting to
integrin α
v
β
3
-rich tumor cells. J Am Chem Soc 2008, 130:75427543.
7. Mi C, Zhang J, Gao H, Wu X, Wang M, Wu Y, Di Y, Xu Z, Mao C, Xu S:
Multifunctional nanocomposites of superparamagnetic (Fe3O4) and
NIR-responsive rare earth-doped up-conversion fluorescent (NaYF4:Yb, Er)
nanoparticles and their applications in biolabeling and fluorescent imaging
of cancer cells. Nanoscale 2010, 2:11411148.
8. Chen ZL, Sun Y, Huang P, Yang XX, Zhou XP: Studies on preparation of
photosensitizer loaded magnetic silica nanoparticles and their anti-
tumor effects for targeting photodynamic therapy. Nanoscale Res Lett
2009, 4:400408.
9. Yang C, Wu J, Hou Y: Fe
3
O
4
nanostructures: synthesis, growth
mechanisms, properties and application. Chem Commun 2011,
47:51305141.
10. Wang X, Zhang R, Wu C, Dai Y, Song M, Gutmann S, Gao F, Lu G, Li J, Li X,
Guan Z, Fu D, Chen B: The application of Fe
3
O
4
nanoparticles in cancer
research: a new strategy to inhibit drug resistance. J Biomed Mater Res A
2007, 80A(4):852860.
11. Gong P, Li H, He X, Wang K, Hu J, Tan W, Zhang S, Yang X: Preparation and
antibacterial activity of Fe
3
O
4
@Ag nanoparticles. Nanotechnology 2007,
18:17. 285604.
12. Liu X, Hu Q, Fang Z, Wu Q, Xie Q: Carboxyl enriched monodisperse
porous Fe
3
O
4
nanoparticles with extraordinary sustained-release
property. Langmuir Lett 2009, 25(13):72447248.
13. Covaliu CI, Berger D, Matei C, Diamandescu L, Vasile E, Cristea C, Ionita V,
Iovu H: Magnetic nanoparticles coated with polysaccharide polymers for
potential biomedical applications. J Nanopart Res 2011, 13:61696180.
14. Wu KT, Kuo PC, Yao YD, Tsai EH: Magnetic and optical properties of Fe
3
O
4
nanoparticle ferrofluids prepared by coprecipitation technique. IEEE Trans
Magn 2001, 37(4):26512653.
15. Narsinga Rao G, Yao YD, Chen YL, Wu KT, Chen JW: Particle size and
magnetic field-induced optical properties of magnetic fluid
nanoparticles. Phys Rev E 2005, 72:16.
16. Liu T, Chen X, Di Z, Zhang J: Tunable magneto-optical wavelength filter
of long-period fiber grating with magnetic fluids. Appl Phys Lett 2007,
91:121116.
17. Li J, Liu X, Lin Y, Bai L, Li Q, Chen X: Field modulation of light transmission
through ferrofluid film. Appl Phys Lett 2007, 91:13. 253108.
18. Chieh JJ, Hong CY, Yang SY, Horng HE, Yang HC: Study on magnetic fluid
optical fiber devices for optical logic operations by characteristics of
superparamagnetic nanoparticles and magnetic fluids. J Nanopart Res
2010, 12:293300.
19. Xia SH, Wang J, Lu ZX, Zhang F: Birefringence and magneto-optical
properties in oleic acid coated Fe
3
O
4
nanoparticles: application for
optical switch. Int J Nanoscience 2011, 10(3):515520.
20. Balberg I, Pankove JI: Optical measurements on magnetite single crystals.
Phys Rev Lett 1971, 27(9):596599.
21. Park JH, Tjeng LH, Allen JW, Metcalf P, Chen CT: Single-particle gap above
the Verwey transition in Fe
3
O
4
. Phys Rev B 1997, 55(19):813817.
22. Jordan K, Cazacu A, Manai G, Ceballos SF, Murphy S, Shvets IV: Scanning
tunneling spectroscopy study of the electronic structure of Fe
3
O
4
surface. Phys Rev B 2006, 74:16. 085416.
23. Buchenau U, Müller I: Optical properties of magnetite. Solid State Commun
1972, 11:1291 1293.
24. Muret P: Optical absorption in polycrystalline thin films of magnetite at
room temperature. Solid State Commun 1974, 14:11191122.
25. Schlegel A, Alvarado SF, Wachter P: Optical properties of magnetite
(Fe
3
O
4
). J Phys C: Solid State Phys 1979, 12:11571164.
26. Fontijn WFJ, van der Zaag PJ, Devillers MAC, Brabers VAM, Metselaar R:
Optical and magneto-optical polar Kerr spectra of Fe
3
O
4
and Mg
2+
-or
Al
3+
-substituted Fe
3
O
4
. Phys Rev B 1997, 56(9):54325442.
27. Yasumori A, Matsumoto H, Hayashi S, Okada K: Magneto-optical properties
of silica gel containing magnetite fine particles. J Solgel Sci Tech 2000,
18:249258.
28. Barnakov YA, Scott BL, Golub V, Kelley L, Reddy V, Stokes KL: Spectral
dependence of Faraday rotation in magnetite-polymer nanocomposites.
J Phys Chem Solids 2004, 65:10051010.
29. Roychowdhury A, Pati SP, Mishra AK, Kumar S, Das D: Magnetically
addressable fluorescent Fe
3
O
4
/ZnO nanocomposites: structural, optical
and magnetization studies. J Phys Chem Solids 2013, 74:811818.
30. Evlyukhin AB, Reinhardt C, Seidel A, Lukyanchuk BS, Chichkov BN: Optical
response features of Si-nanoparticle arrays. Phys Rev B 2010,
82(4):112. 045404.
31. Marenich AV, Cramer CJ, Truhlar DG: Reduced and quenched polarizabilities
of interior atoms in molecules. Chem Sci 2013, 4:23492356.
32. Kang YS, Risbud S, Rabolt JF, Stroeve P: Synthesis and characterization of
nanometer-size Fe
3
O
4
and γ-Fe
3
O
4
particles. Chem Mater 1996,
8:22092211.
33. Chen L, Yang WJ, Yang CZ: Preparation of nanoscale iron and Fe
3
O
4
powders in a polymer matrix. J Mater Sci 1997, 32:35713575.
34. Long Y, Chen Z, Duvali JL, Zhang Z, Wan M: Electrical and magnetic
properties of polyaniline/Fe
3
O
4
nanostructures. Physica B 2005,
370:121130.
35. Banert T, Peuker UA: Preparation of highly filled super-paramagnetic
PMMA-magnetite nanocomposites using the solution method. J Mater
Sci 2006, 41:30513056.
36. Li D, Jiang D, Chen M, Xie J, Wu Y, Dang S, Zhang J: An easy fabrication of
monodisperse oleic acid-coated Fe
3
O
4
nanoparticles. Mater Lett 2010,
64:24622464.
37. Gnanaprakash G, Mahadevan S, Jayakumar T, Kalyanasundaram P, Philip J, Raj B:
Effect of initial pH and temperature of iron salt solutions on formation of
magnetite nanoparticles. Mater Chem Phys 2007, 103:168175.
38. Tural B, Özkan N, Volkan M: Preparation and characterization of polymer
coated superparamagnetic magnetite nanoparticle agglomerates. J Phys
Chem Solids 2009, 70:860866.
39. Lan Q, Liu C, Yang F, Liu S, Xu J, Sun D: Synthesis of bilayer oleic acid-
coated Fe
3
O
4
nanoparticles and their application in pH-responsive
Pickering emulsions. J Coll Interf Sci 2007, 310:260269.
Milichko et al. Nanoscale Research Letters 2013, 8:317 Page 6 of 7
http://www.nanoscalereslett.com/content/8/1/317
40. Milichko VA, Dzyuba VP, Kulchin YN: Unusual nonlinear optical properties
of SiO
2
nanocomposite in weak optical fields. Appl Phys A 2013,
11(1):319322.
41. Sheik-Bahae M, Said AA, Wei TH, Hagan DJ, Van Stryland EW: Sensitive
measurement of optical nonlinearities using a single beam. IEEE J
Quantum Electron 1990, 26(4):760769.
42. Liu X, Guo S, Wang H, Hou L: Theoretical study on the closed-aperture
Z-scan curves in the materials with nonlinear refraction and strong
nonlinear absorption. Opt Commun 2001, 197:431437.
43. Ganeev RA, Ryasnyansky AI, Stepanov AL, Usmanov T: Nonlinear optical
response of silver and copper nanoparticles in the near-ultraviolet
spectral range. Phys Sol State 2004, 46(2):351356.
44. AlL E, Rosen M: Quantum size level structure of narrow-gap
semiconductor nanocrystals: effect of band coupling. Phys Rev B 1998,
58(11):71207135.
45. Bennett BR, Soref RA, Del Alamo J: Carrier-induced change in refractive
index of InP, GaAs, and InGaAsP. IEEE J Quantum Electron 1990,
26(1):113122.
46. Veselago VG: The electrodynamics of substances with simultaneously
negative values of ε and μ. Physics-Uspekhi 1968, 10:509514.
47. Yu ZG, Krishnamurthy S, Guha S: Photoexcited-carrier-induced refractive
index change in small bandgap semiconductors. J Opt Soc Am B 2006,
23(11):23562360.
48. Akhmanov A, Nikitin SY: Physical Optics. Oxford: Oxford University Press; 1997.
doi:10.1186/1556-276X-8-317
Cite this article as: Milichko et al.: Photo-induced electric polarizability of
Fe
3
O
4
nanoparticles in weak optical fields. Nanoscale Research Letters
2013 8:317.
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