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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.

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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.