Dielectric properties of nematic liquid crystals with Fe₃O₄ nanoparticles in direct magnetic field
Researched within the frequency range 10⁻¹–10⁶ Hz were dielectric properties of pure 6CHBT liquid crystals and 6CHBT ones with the impurity of Fe₃O₄ nanoparticles that have the mean diameter 5 nm and weight concentration 10⁻⁴ %. The study was performed without and under the influence of direct ma...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2009
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irk-123456789-1188822017-06-01T03:02:50Z Dielectric properties of nematic liquid crystals with Fe₃O₄ nanoparticles in direct magnetic field Gornitska, O.P. Koval’chuk, A.V. Koval’chuk, T.N. Kopčanský, P. Timko, M. Zavisova, V. Koneracká, M. Tomašovičová, N. Jadzyn, J. Studenyak, I.P. Researched within the frequency range 10⁻¹–10⁶ Hz were dielectric properties of pure 6CHBT liquid crystals and 6CHBT ones with the impurity of Fe₃O₄ nanoparticles that have the mean diameter 5 nm and weight concentration 10⁻⁴ %. The study was performed without and under the influence of direct magnetic field with the induction 0.45 and 0.60 T. It has been shown that the magnetic field influences on the parameters of the near-electrode area of liquid crystal. In the case of liquid crystal with magnetic nanoparticles, the parameter changes caused by the magnetic field depend on the induction value. 2009 Article Dielectric properties of nematic liquid crystals with Fe₃O₄ nanoparticles in direct magnetic field / O.P. Gornitska, A.V. Koval'chuk, T.N. Koval'chuk, P. Kopcansky, M. Timko, V. Zavisova, M. Koneracka, N.Tomasovicova, J. Jadzyn, I.P. Studenyak // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2009. — Т. 12, № 3. — С. 309-314. — Бібліогр.: 19 назв. — англ. 1560-8034 PACS 61.30.Gd, 75.30.Hx, 77.84.Nh http://dspace.nbuv.gov.ua/handle/123456789/118882 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
| language |
English |
| description |
Researched within the frequency range 10⁻¹–10⁶ Hz were dielectric properties
of pure 6CHBT liquid crystals and 6CHBT ones with the impurity of Fe₃O₄ nanoparticles
that have the mean diameter 5 nm and weight concentration 10⁻⁴ %. The study was
performed without and under the influence of direct magnetic field with the induction
0.45 and 0.60 T. It has been shown that the magnetic field influences on the parameters
of the near-electrode area of liquid crystal. In the case of liquid crystal with magnetic
nanoparticles, the parameter changes caused by the magnetic field depend on the
induction value. |
| format |
Article |
| author |
Gornitska, O.P. Koval’chuk, A.V. Koval’chuk, T.N. Kopčanský, P. Timko, M. Zavisova, V. Koneracká, M. Tomašovičová, N. Jadzyn, J. Studenyak, I.P. |
| spellingShingle |
Gornitska, O.P. Koval’chuk, A.V. Koval’chuk, T.N. Kopčanský, P. Timko, M. Zavisova, V. Koneracká, M. Tomašovičová, N. Jadzyn, J. Studenyak, I.P. Dielectric properties of nematic liquid crystals with Fe₃O₄ nanoparticles in direct magnetic field Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Gornitska, O.P. Koval’chuk, A.V. Koval’chuk, T.N. Kopčanský, P. Timko, M. Zavisova, V. Koneracká, M. Tomašovičová, N. Jadzyn, J. Studenyak, I.P. |
| author_sort |
Gornitska, O.P. |
| title |
Dielectric properties of nematic liquid crystals with Fe₃O₄ nanoparticles in direct magnetic field |
| title_short |
Dielectric properties of nematic liquid crystals with Fe₃O₄ nanoparticles in direct magnetic field |
| title_full |
Dielectric properties of nematic liquid crystals with Fe₃O₄ nanoparticles in direct magnetic field |
| title_fullStr |
Dielectric properties of nematic liquid crystals with Fe₃O₄ nanoparticles in direct magnetic field |
| title_full_unstemmed |
Dielectric properties of nematic liquid crystals with Fe₃O₄ nanoparticles in direct magnetic field |
| title_sort |
dielectric properties of nematic liquid crystals with fe₃o₄ nanoparticles in direct magnetic field |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2009 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/118882 |
| citation_txt |
Dielectric properties of nematic liquid crystals with Fe₃O₄ nanoparticles in direct magnetic field / O.P. Gornitska, A.V. Koval'chuk, T.N. Koval'chuk, P. Kopcansky, M. Timko, V. Zavisova, M. Koneracka, N.Tomasovicova, J. Jadzyn, I.P. Studenyak // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2009. — Т. 12, № 3. — С. 309-314. — Бібліогр.: 19 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 3. P. 309-314.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
309
PACS 61.30.Gd, 75.30.Hx, 77.84.Nh
Dielectric properties of nematic liquid crystals
with Fe3O4 nanoparticles in direct magnetic field
O.P. Gornitska1, A.V. Koval’chuk1,2, T.N. Koval’chuk3, P. Kopčanský4, M. Timko4, V. Zavisova4,
M. Koneracká4, N. Tomašovičová4, J. Jadzyn5, I.P. Studenyak6
1National Aviation University, Institute of Innovative Technologies
1, Cosmonaut Komarov str., 03058 Kyiv, Ukraine
2Institute of Physics, National Academy of Science of Ukraine, 46, prospect Nauky, 03028 Kyiv, Ukraine
3V. Lashkaryov Institute of Semiconductor Physics, National Academy of Science of Ukraine,
45, prospect Nauky, 03028 Kyiv, Ukraine
4Institute of Experimental Physics, Slovak Academy of Sciences, 47, Watsonova str., 04001 Kosice, Slovak Republic
5Institute of Molecular Physics, Polish Academy of Sciences, 16, Smoluchowskiego str., 60179 Poznan, Poland
6Uzhgorod National University, 46, Pidhirna str., 88000 Uzhgorod, Ukraine
Abstract. Researched within the frequency range 10-1–106 Hz were dielectric properties
of pure 6CHBT liquid crystals and 6CHBT ones with the impurity of Fe3O4 nanoparticles
that have the mean diameter 5 nm and weight concentration 10-4 %. The study was
performed without and under the influence of direct magnetic field with the induction
0.45 and 0.60 T. It has been shown that the magnetic field influences on the parameters
of the near-electrode area of liquid crystal. In the case of liquid crystal with magnetic
nanoparticles, the parameter changes caused by the magnetic field depend on the
induction value.
Keywords: dielectric properties of liquid crystals, magnetic impurities, orientation of
liquid crystals.
Manuscript received 14.03.09; accepted for publication 14.05.09; published online 30.06.09.
1. Introduction
Using the liquid crystals (LC) is mainly determined by the
possibility of substantial variation of their properties under
the influence of weak fields. In most devices that were
already elaborated and widely used (LC displays), the
different types of electro-optical effects are used. To
create the electric field in a LC cell, it is necessary to
deposite the electrodes transparent in the visible spectrum
onto the boundary surfaces. Using the electro-optical
effects, one needs to take into account the influence of
near-electrode processes [1, 2]. All these factors that may
create substantial problems (one of the basic problems is
increase of the electro-optical response time) would be
avoided by the influence of magnetic field on LC.
Magneto-optical effects in LC are revealed and
studied for a relative long time. Their practical usage is
restrained because anisotropy of magnetic permittivity of
LC is far less than that of the dielectric one. Therefore,
the rotational motion of LC molecules can be carried out
under the influence of sufficiently strong alternative
magnetic fields (units, tens of T). Up to date, devices for
creation of these fields are realized only in laboratory
conditions and are not used in practice for their rather
high cost.
It is possible to substantially increase the LC
magnetic anisotropy due to the introduction of magnetic
impurities (basically ferric oxides). As shown in [3, 4],
in these ferronematics, the magnetic field induction of
the Fredericksz transition differs from that for pure LC.
To control magnetic impurity behavior in LC, they have
to show certain characteristics: (i) small and controlled
sizes and form, (ii) do not chemically interact with the
LC molecules, and (iii) comparatively (with the LC
molecules) weakly interact with each other. Magnetic
nanoparticles obey to all these requirements, the
technology of their preparation was successfully
developed for recent few years.
In Refs [3-9], studied was the influence of
magnetic nanoparticles on the Fredericksz transitions
under the action of either electric field or magnetic one
or under the simultaneous action of these fields in
ferronematics based on different LC. It should be noted
that experimental investigations were carried out mainly
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 3. P. 309-314.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
310
for those conditions (orientation of molecules in a cell,
orientation of the electric and magnetic field relative to
orientation of director), for which detailed theoretical
calculations were obtained [10].
It is known that in the case for reorientation of
molecules (Fredericksz effect), the initial stage of
molecular rotational motion takes place in the near-
electrode area of a sample [11, 12]. Therefore, the
investigation of processes occurred here is enough
important for understanding the features of the very
Fredericksz effect.
As shown in Refs [13, 14], the dielectric
spectroscopy is the effective method to research the
parameter change in a near-electrode area. Therefore, the
aim of this work is to study the dielectric spectra of LC
with magnetic nanoparticles in the direct magnetic field.
To study the particular initial stage of molecular
rotational motion, the measurements were carried out
under the influence of the electric and magnetic fields,
the voltage and induction values of which were
sufficiently less than those necessary for complete
reorientation of molecules. It should be noted that such
experimental studies have not been performed before.
2. Materials and methods
The synthesis of the spherical magnetic nanoparticles
was based on coprecipitation of Fe2+ and Fe3+ salts by
NH4OH. To obtain a Fe3O4 precipitate, FeSO4·7H2O and
FeCl3·6H2O were dissolved in deionized water by
vigorous stirring (the ratio Fe3+:Fe2+ was 2:1). The
solution was heated to 60 °C and 25 % NH4OH was
added. The precipitate was isolated from solution by
magnetic decantation and washing with water. Particles
were coated with oleic acid as a surfactant at 80 °C.
The magnetic properties were estimated by
magnetization measurements using a vibrating sample
magnetometer (Fig. 1), the saturation magnetization was
65 mT. Size and morphology of the particles were
determined by transmission electron microscopy (TEM)
(Fig. 2). The mean diameter of the magnetic
nanoparticles was 4.8 nm (obtained by TEM). A
histogram of the size distribution of the spherical
magnetic particles is shown in Fig. 3.
The studied ferronematic samples were based on
the thermotropic nematic 4-(trans-4´-n-
hexylcyclohexyl)-isothiocyanatobenzene (6CHBT).
6CHBT is a low-melting enantiotropic liquid crystal
with high chemical stability [15]. The temperature of the
nematic-to-isotropic transition (clearing point) of the
studied nematic is TNI = 42.8 °C. The nematic samples
were doped with a magnetic suspension that consists of
nearly spherical Fe3O4 magnetic particles coated with
oleic acid as a surfactant. The doping was simply made
by adding this suspension, under continuous stirring, to
the liquid crystal in the isotropic phase. Due to the small
volume concentrations of the magnetic particles (~10−4)
and surfactant in the prepared ferronematic samples, the
interparticle dipole-dipole interactions are avoided.
Fig. 1. Magnetization curve of prepared magnetic paste.
Frequency dependences of resistance R and
capacity C were measured by using the oscilloscopic
method [2, 16] under condition that the equivalent
scheme of sample is the parallel linked resistance and
capacity. The measuring signal had a triangular form;
the amplitude was 0.25 V. The frequency of the
measuring signal was changing within the range 510-2-
105 Hz.
Based on the known R and C, and were determined.
The direct magnetic field was created by two or four
SaCo magnets that were located on both sides of glass
substrates that bound the liquid crystal. In this case, the
magnetic field was aligned with the electric one. The
distance between the magnets is equal to the thickness of
the measuring device cell, the area of magnets many
times exceeded the square of electrodes, suggesting that
the magnetic field in a sample is homogeneous. The
magnetic field induction was measured by the calibrated
Hall sensor. Dielectric properties of the samples were
measured at the temperature 293 K.
Fig. 2. TEM image of magnetic particles.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 3. P. 309-314.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
311
Fig. 3. Histogram of size distribution for spherical magnetic
particles.
3. Experimental results and discussions
3.1. Dielectric properties of pure LC
Fig. 4 presents the frequency dependences (1) and
(2) of the planar oriented pure 6СНВТ. The analysis of
dielectric spectrum gives grounds to divide it into two
parts: the part A ( f 10 Hz) where substantial
dispersion of complex dielectric permittivity
components is observed, and the part В ( f 10 Hz)
where is frequency independent and decreases
linearly with increasing the frequency (a sample
resistance is frequency independent). As was shown in
[2], the part B relates to those frequencies when near-
electrode processes do not influence on the sample
parameters (the electric field in a sample is
homogeneous). Parameters determined in this part
characterize the bulk properties of LC: – the bulk
dielectric permittivity V, and – the conductivity AC.
The AC value was determined as follows:
0AC , (1)
10-1 100 101 102 103 104
10-1
100
101
102
103
BA
2
1
f, Hz
Fig. 4. Frequency dependences of (1) and (2) for planar-
oriented 6СНВТ at the temperature 293 K; thickness of the
sample is 20 m.
Table.
Sample B, T AC,
S/m
V W,
nm
, s
6CHBT 0 1.910-8 5.5 18 1.0
6CHBT 0.45 1.810-8 5.8 21 1.5
6CHBT 0.60 1.910-8 5.8 21 1.4
6CHBT+Fe3O4 0 1.910-8 6.1 21 1.6
6CHBT+Fe3O4 0.45 1.910-8 6.6 24 1.8
6CHBT+Fe3O4 0.60 2.110-8 6.6 25 1.8
where 0 is the dielectric constant, and = 2f is the
cyclic frequency. The estimated values of V and AC are
summarized in Table. A comparison of the obtained AC
value for 6СНВТ with the parameters for the other LC
shows sufficiently high purity of the LC material under
study.
The part B describes the initial stage of near-
electrode processes. As was shown in [17, 18], the
planar-oriented LC with positive anisotropy of dielectric
permittivity is characterized by a relaxation process
caused by dipole polarization in the near-electrode area
of the sample. At the same time, in the very near-
electrode area of a sample, a current is mainly provided
by the rotational motion of dipoles within the range of
angles equal to a fluctuation of the order parameter, and
in the bulk – by ion transport. Our investigations of this
relaxation process showed [17] that the dependence
() (known as the Cole-Cole diagram) must be
approximated by a semicircle. Similarly to dipole
relaxation in the sample bulk, theoretically such
relaxation process is described by the Debye equation:
i
s
1
* , (2)
where * is the complex dielectric permittivity, s and
are the dielectric permittivities for the frequencies f = 0
and = , accordingly, is the time of dielectric
relaxation.
Analysis of the Cole-Cole diagrams for the samples
obtained without and under the influence of the magnetic
field showed that these diagrams are described by the
equation (2) with an experimental error that does not
exceed 5 %. Thus, it is possible to consider that, at the
initial stage of molecular reorientation, a linear electro-
optical effect may be substantial in the near-electrode
area of the sample. Different polar impurities and, in
particular, magnetic nanoparticles can influence on the
parameters of this process.
Among the basic parameters that characterize the
Debye dispersion is the time of dielectric relaxation. As
shown in Table, this time is equal to one second for pure
LC without the magnetic field.
The difference between the relaxation process
resulting from dipole polarization in the near-electrode
area of a sample and that in the bulk of a sample is rather
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 3. P. 309-314.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
312
high values of and in the former case. Fig. 4 shows
that they exceed the value of 103 for the frequency
f = 10-1 Hz. As was shown in [2], it is caused by a
heterogeneous distribution of the electric field in a
sample. If to suppose that the parameters of near-
electrode areas near each of the electrodes are identical
(the capacitances of near-electrode areas are identical)
and the dielectric permittivity of near-electrode area
equals V, then using the sample maximal capacitance
(obtained using the analysis of the Cole-Cole diagram)
for this relaxation process, it is possible to estimate the
thickness of a near-electrode area [2, 17]
s
Vd
W
2
. (3)
The W value for pure LC is also listed in Table. It
equals 18 nm and differs little by the order of value from
the same parameter for other LCs [2, 17, 18].
3.2. Influence of the magnetic field on dielectric
properties of LC
Fig. 5 shows frequency dependences of the ratio of
dielectric permittivity for pure 6СНВТ under the action
of the magnetic field В to that without the magnetic
field 0 for (1, 2), (3, 4) and different values of the
induction of 0.45 T (1, 3) and 0.60 T (2, 4). When
analyzing the dielectric spectrum for pure LC, we
consider separately the changes for bulk and near-
electrode areas of the sample.
Fig. 5 and Table show that the magnetic field results
to insignificant decrease of AC and increase of V. As the
AC changes were close to experimental errors, the reasons
that could cause these changes were not analyzed.
Changes of the V value under the influence of the
magnetic field are attributable to the partial rotational
motion of molecules. This rotational motion may be
realized only within the range of angles that relate to
fluctuations of the order parameter. Therefore, in practice
the voltage for the Fredericksz effect could not have a
threshold value. It is precisely this fact that explains that
the changes under the magnetic field are identical for two
different В values. It should be noted that the В /0 ratio
for the part A does not depend on the frequency (Fig. 5).
And vice versa, for the part B the dispersion of the В /0
ratio is observed, moreover, the frequency dependences of
В/0 ratio differ essentially from those of В/0 one. As
follows from Fig. 5, the В/0 minimum value equals 0.92
at the frequency close to 0.3 Hz, and its maximal value
equals 1.08 at f ≈ 3 Hz. At the same time, the В/0 ratio
has only a minimum value 0.9 at the frequency 2 Hz. It is
also significant that, for pure LC, the В /0 ratio and
parameters of bulk part of the sample do not depend
substantially on the value of the magnetic field induction.
As for the characteristics of the near-electrode
relaxation process, the magnetic field results in the
increase of the dielectric relaxation time and thickness of
the near-electrode area (Table). It should be noted that
the change of these parameters does not substantially
depend on the value of the magnetic field, too.
3.3. Influence of magnetic nanoparticles on dielectric
properties of LC
Fig. 6 presents the frequency dependences of ratio of the
dielectric permittivity value for LC with magnetic
nanoparticles LM to that for pure 6СНВТ L at В = 0.
From Table we see that presence of the magnetic
particles does not influence on the AC value but cause
the increase of the V value. Invariability of the AC value
when introducing the magnetic nanoparticles suggests
that these impurities were rather “pure” and did not
influence on the concentration of charge carriers in LC.
This fact is reasonably important for the analysis of the
obtained results.
10-1 100 101 102 103 104
0.8
1.0
1.2
1.4
1.6
2
1
LM
/
L
f, Hz
Fig. 6. Frequency dependences for the ratio of dielectric
permittivity value for LC with magnetic nanoparticles LM to
that for pure LC L at the temperature 293 K. The induction of
magnetic field is В = 0; thickness of the sample is 20 m.
10-1 100 101 102 103 104
0.90
0.95
1.00
1.05
1.10
4
3
1
2
B
/
f, Hz
Fig. 5. Frequency dependences for the ratio of dielectric
permittivity value for 6СНВТ in the magnetic field В to
that without the magnetic field 0 for (1, 2), (3, 4) and
different values of the magnetic field induction 0.45 T
(1, 3) and 0.60 T (2, 4) at the temperature 293 K.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 3. P. 309-314.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
313
The increase of dielectric permittivity when
introducing the magnetic nanoparticles can be explained
by two factors: (i) a rather high value of the dielectric
permittivity of nanoparticles and (ii) a partial change in
molecular orientation of LC [19]. Taking into account
that a concentration of magnetic nanoparticles was rather
small (10-4 %), the change of dielectric permittivity value
of LC due to the implanted impurities is determined as
follows
VM
VM
Vc
ε3ε
εε
ε3
, (4)
where с = 10-4 % is the concentration of magnetic
nanoparticles, M is the dielectric permittivity of
magnetic nanoparticles.
When = 0.6, from the equation (4) it follows
that this change can be caused by nanoparticles with a
negative value of dielectric permittivity. It does not
conform to the properties of the nanoparticles in any
way. Therefore, the most probable explanation for the
dielectric permittivity change due to Fe3O4 nanoparticles
can be influence of these nanoparticles on the pretilt
angle of LC molecules.
As in the case of the magnetic field influence on
properties of pure LC, the frequency dispersion of LM /L
ratio for the part В differs for dielectric permittivity of
each component. If the LM/L ratio has the maximum
value (1.6) at 5 Hz and minimum one (0.9) at 10-1 Hz,
the LM/L ratio has the only minimum value (0.85) at
frequency 0.3 Hz.
The presence of magnetic nanoparticles causes
changes in parameters of the near-electrode relaxation
process. As seen from Table, implantation of Fe3O4
nanoparticles into LC results in increasing the relaxation
time and thickness of the near-electrode area. Taking
into account Ref. [18], it is possible to suppose that the
relaxation time increase is a result of increase in the
energy of adhesion of LC molecules to substrate. The
influence of magnetic nanoparticles on the value of
adhesion energy of LC molecules to substrate was
studied in detail in Ref. [7].
3.4. Influence of the magnetic field on dielectric
properties of LC with magnetic nanoparticles
Fig. 7 shows the frequency dependences of the ratio of
dielectric permittivity for 6СНВТ with Fe3O4
nanoparticles under the influence of magnetic field В to
that without magnetic field 0 for (1, 2), (3, 4) and
different values of the magnetic field induction 0.45 T
(1, 3) and 0.60 T (2, 4).
Like to the case of pure LC, the magnetic field
increases the V value. The V variation for two values of
the magnetic field induction does not depend on the B
value within the range of experimental errors. Therefore,
the results of magnetic field influence on the V value for
6СНВТ with Fe3O4 nanoparticles and pure 6СНВТ are
not distinguished. As for the AC value, it depends on the
value of the magnetic field (Table), most probably the
reason of this is a change of bulk properties of LC and,
in particular, mobility of charge carriers.
The most cardinal differences between the
dielectric spectra of В /0 ratio for 6СНВТ with Fe3O4
nanoparticles and pure 6СНВТ are observed for the
part В. Unlike the frequency dependence of В/0 ratio
for pure 6СНВТ, the similar frequency dependence for
LC with nanoparticles has only one maximum value at
the frequency close to 0.4 Hz. It is also significant that
this particular maximal value (unlike for pure LC)
depends on the value of the magnetic field.
A comparison of Figs 5 and 7 suggests that for the
part B the В/0 ratios for LC with nanoparticles and
for pure LC differ substantially, too. Unlike the pure LC,
the В/0 ratio for LC with nanoparticles has a low
maximum value at f ≈ 1 Hz, and then observed is the
sharp drop in this value with frequency decreasing. It is
also significant that the value of В/0 ratio depends on
the magnetic field value.
The analysis of parameters inherent to the near-
electrode relaxation process shows that, like to the case
of pure LC, the influence of magnetic field on LC with
nanoparticles results in the increase of the relaxation
time and thickness of near-electrode layer. Thus, it is
important to note that the thickness of the near-electrode
area depends on the induction.
4. Conclusions
1. The method of dielectric spectroscopy is rather
effective to analyze the influence of nanoparticles at the
initial stage of the Fredericksz effect in the magnetic
or/and electric fields.
2. From the analysis of the frequency dependence
of ratio of the dielectric permittivity for LC with
10-1 100 101 102 103 104
0.4
0.6
0.8
1.0
1.2
1
3
4
2
B
/
0
f, Hz
Fig. 7. Frequency dependences for the ratio of dielectric
permittivity value В for 6СНВТ with Fe3O4 nanoparticles
in the magnetic field to that without the magnetic field 0
for (1, 2), (3, 4) and different values of the magnetic
field induction 0.45 T (1, 3) and 0.60 T (2, 4) at the
temperature 293 K.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2009. V. 12, N 3. P. 309-314.
© 2009, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
314
magnetic nanoparticles LM to that for pure LC L, it is
possible to find those frequencies, at which the changes
of parameters of the materials under study are maximal.
These frequencies relate to the part of dielectric
spectrum caused by near-electrode processes.
3. The low-frequency relaxation process is caused
by dipole polarization of molecules in the near-electrode
area and described by the Debye equation. The
relaxation time (units of seconds) and thickness of the
near-electrode area (tens of nanometers) were estimated.
It has been shown that these parameters are increased
when implanting the magnetic nanoparticles into LC and
under the action of the magnetic field. In the case of LC
with nanoparticles, the thickness of near-electrode area
depends on the induction value.
4. Both for pure LC and LC with magnetic
nanoparticles, the magnetic field more substantially
influences on the parameters of near-electrode area than
on bulk properties of samples. The ratios of the dielectric
permittivity values under the magnetic field to that
without the magnetic field are non-monotonous
functions of frequencies, which relate to the near-
electrode relaxation process. The frequency dependences
of these ratios differ essentially for pure LC and LC with
magnetic nanoparticles.
5. The ratio of the dielectric permittivity values
under the magnetic field to that without the magnetic
field in a greater measure depends on the magnetic field
induction in the case of LC with nanoparticles than in
the case of pure LC. It gives grounds to develop new
materials for the indicators of the magnetic field.
Acknowledgements
This work was supported by the Slovak Academy of
Sciences, in the framework of CEX-NANOFLUID, the
project SAV-FM-EHP-2008-01-01, MNT-ERA Net
2008-022-SK, the projects VEGA 0077, APVV 0173-
06, 0509-07 and Ministry of Education Agency for
Structural Funds of EU in the frame of the project
26220120021.
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