Effect of Synthesis Method of La1 − xSr x MnO3 Manganite Nanoparticles on Their Properties
Shlapa et al. Nanoscale Research Letters
Effect of Synthesis Method of La1 − xSrxMnO3 Manganite Nanoparticles on Their Properties
Yulia Shlapa 0
Sergii Solopan 0
Anatolii Belous 0
Alexandr Tovstolytkin
0 V. I. Vernadskii Institute of General and Inorganic Chemistry of the NAS of Ukraine , 142, Palladina ave., 32/34, Kiev 03680 , Ukraine
Nanoparticles of lanthanum-strontium manganite were synthesized via different methods, namely, sol-gel method, precipitation from non-aqueous solution, and precipitation from reversal microemulsions. It was shown that the use of organic compounds and non-aqueous media allowed significantly decreasing of the crystallization temperature of nanoparticles, and the single-phased crystalline product was formed in one stage. Morphology and properties of nanoparticles depended on the method and conditions of the synthesis. The heating efficiency directly depended on the change in the magnetic parameters of nanoparticles, especially on the magnetization. Performed studies showed that each of these methods of synthesis can be used to obtain weakly agglomerated manganite nanoparticles; however, particles synthesized via sol-gel method are more promising for use as hyperthermia inducers. PACS: 61.46.Df 75.75.Cd 81.20. Fw
Manganite nanoparticles; Sol-gel; Non-aqueous solution; Microemulsion; Magnetization; Specific loss power
Background
Structure and properties of magnetic materials differ from
those of bulk materials in the transition to the nanoscale
[
1
]. In addition to possible practical application in various
magnetic sensors, magnetic recording systems [
2
],
magnetic nanoparticles are of particular interest in the
possibilities of practical use in medicine. Researchers study
many possible medical directions of their application:
delivery of drugs and biological objects [
3, 4
], biomarkers
[5], magnetic resonance imaging (MRI) [
6, 7
], etc.
One of the promising directions for medical
application of magnetic nanoparticles is hyperthermia—locally
heating the oncological tumors under the action of an
alternating magnetic field to 43–45 °C, at which the
tumor cells die [
8
]. Application of an external alternating
magnetic field is accompanied by a number of problems:
uneven and uncontrolled heating tumor, risk of
overheating and destruction of healthy tissues, and
impossibility of heating the deep-seated tumors. Therefore, in
1993, Prof. Jordan suggested the idea of magnetic
hyperthermia, which consisted in the use of the
magnetic nanoparticles and an alternating magnetic field [
9
].
In this case, the magnetic nanoparticles must be
previously injected into the tumor, and such tumor must be
affected by an alternating magnetic field. Particle
temperature will increase by the absorption of magnetic
energy and provide the local heating. However, such
nanoparticles must satisfy a number of requirements:
small sizes and weak agglomeration of nanoparticles;
such particles must be single domain and
superparamagnetic (to prevent interactions between individual
nanoparticles in the absence of magnetic field), and they
must effectively heat up in the alternating magnetic field
to the required temperatures (43–45 °C) and
demonstrate high specific loss power (SLP) values.
At present, magnetic nanoparticles of the magnetite
Fe3O4 with a spinel structure are actively investigated as
possible mediators of hyperthermia treatment [
7, 10, 11
].
Magnetite is characterized by a high value of Curie
temperature (TC ≈ 580 °C) [
12
]—the transition
temperature from magnetic to paramagnetic state. Since
magnetic nanoparticles heat up in an alternating
magnetic field only when they are in a magnetic state (up to
TC point), in the case of magnetite, the heating is
uncontrollable up to high temperatures. It may result in
overheating and destroying the healthy tissues.
To prevent this problem, it is important to search for
the alternative materials, in which the Curie point will
be in the temperature range that is necessary for
hyperthermia. In this case, heterosubstituted manganites of
lanthanum-strontium La1 − xSrxMnO3 (LSMO) with the
distorted perovskite structure are of particular interest.
They have the phase transition temperature near 45 °C
that provides the controlled heating temperature without
any additional thermoregulative devices.
Crystallization energy of materials with the perovskite
structure is much higher than that for spinel structure
[
13
]. Due to this reason, an amorphous phase is always
formed in the first stage regardless of the method of
synthesis of nanoparticles with the perovskite structure
from solutions. Preparation of the crystalline product
requires additional temperature treatment that leads to
the agglomeration of the nanoparticles. Investigations
described in [
14
] showed that formation of the
crystalline structure after precipitation from aqueous solutions
and further heating the powder is a multi-stage process;
single-phased crystalline produ (...truncated)