The size effect of magnetic nanoparticles provides a various magnetic characteristic as a change of domain size. We report, synthesis of core-shell iron oxide and magnetic properties. Iron oxide particles were synthesized by co-precipitation method of iron (III) FeCl3.6H2O, iron (II) FeCl2.4H2O, in the mixture of with or without TEOS to investigated the physical properties. From XRD measurement, it was observed that all iron oxide particles with or without mixture of SiO2 has a hematite phase of a-Fe2O3. From M-H loop measurement, it was observed that the iron oxide without SiO2 has a ferromagnetic characteristic, while the iron oxide with SiO2 showed a medium state as a contribution of superparamagnetic and ferromagnetic properties.
One of the important characteristics of magnetic materials is the measurement of magnetic characteristics through Superconducting Quantum Interference Device (SQUID) especially magnetization temperature dependence M(T)ZFC and MTFC measurement. In this work, we reported magnetization temperature dependence measurements of magnetite nanoparticles without SiO2 encapsulation (Fe3O4) and magnetite nanoparticles with SiO2 encapsulation (Fe3O4.SiO2) at the application of magnetic fields of 100 Oe. The nanoparticles magnetite was synthesized by co-precipitation method. It was calculated that the blocking temperature of magnetite nanoparticles Fe3O4 without and with SiO2 encapsulation is 118.38 K and 209.03 K, respectively. The blocking temperatures of magnetic nanoparticles increase by SiO2 encapsulation.
The magnetic properties and relaxation time of Fe3O4 nanoparticles, and their encapsulation with silicon dioxide (Fe3O4-SiO2), have been successfully investigated by analyzing the temperature dependence of magnetization (()) and the time dependence of magnetization (()), using the SQUID magnetometer measurement. The () measurement results can determine the magnetic parameters and magnetic irreversibility of Fe3O4 and Fe3O4-SiO2 samples. The values of Curie constant (), effective magnetic moment (), and Weiss temperature () are 4.2 (emu.K.Oe/mol), 5.77 , and −349 K, respectively, for the Fe3O4 samples, and 81.3 (emu.K.Oe/mol), 25.49 , and −2440 K, respectively, for the Fe3O4-SiO2 samples. After encapsulation, the broadening peak deviation decreased from 281.6 K to 279 K, indicating that the superparamagnetic interactions increased with the encapsulation process. The magnetic parameters and irreversibility values showed that the superparamagnetic properties increased significantly after encapsulation (Fe3O4-SiO2). From the results of the () measurement, it was found that there was a decrease in the magnetic relaxation time after the encapsulation process, which indicated that the distribution of the nanoparticle size and anisotropy energy increased.
Magnetic nanofluids are a category of nanomaterial which exhibit simultaneously liquid and superparamagnetic properties. These nanofluids are magnetic nanoparticles stably dispersed in liquid carrier. Magnetic nanoparticles with and without SiO2 encapsulation have been successfully synthesized by co-precipitation method from ferrous and ferric precursors dispersed in various liquid. Fe3O4 nanoparticles were investigated by Zeta Potential and HR-TEM to determine the stability of nanoparticles, average particles size and microstructure of nanoparticles. From zeta potential measurements, is was found that the value of zeta potential for Fe3O4 dispersed in ethanol was ± 0,9 mV, while dispersed in di-water was ± 31,1 mV, indicating that nanoparticles Fe3O4 are more stable in DI-water. The increasing of zeta potential indicated the adsorption of negatively charged hydroxyl group to the surface of Fe3O4 nanoparticles. From XRD measurements, it was found that crystal quality of Fe3O4.SiO2 sintering at 80 °C decreased by increasing the volume of tetraethyl orthosilicate (TEOS), while that samples sintering at 1000 °C have a good crystal quality with hexagonal phase of a-Fe2O3.SiO2. From SQUID measurements, it was found that samples of Fe3O4.SiO2 sintering at 80 °C with TEOS volumes of 1 ml and 2 ml showed a paramagnetic like while samples of a-Fe2O3.SiO2 sintering at 1000 °C with the same TEOS volume showed ferrimagnetic properties.
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