Study of Magnetic Properties and Relaxation Time of Nanoparticle Fe(3)O(4)-SiO(2)

The magnetic properties and relaxation time of Fe(3)O(4) nanoparticles, and their encapsulation with silicon dioxide (Fe(3)O(4)-SiO(2)), have been successfully investigated by analyzing the temperature dependence of magnetization ([Formula: see text] ([Formula: see text])) and the time dependence of magnetization ([Formula: see text] ([Formula: see text])), using the SQUID magnetometer measurement. The [Formula: see text] ([Formula: see text]) measurement results can determine the magnetic parameters and magnetic irreversibility of Fe(3)O(4) and Fe(3)O(4)-SiO(2) samples. The values of Curie constant ([Formula: see text]), effective magnetic moment ([Formula: see text]), and Weiss temperature ([Formula: see text]) are 4.2 (emu.K.Oe/mol), 5.77 [Formula: see text] , and −349 K, respectively, for the Fe(3)O(4) samples, and 81.3 (emu.K.Oe/mol), 25.49 [Formula: see text] , and −2440 K, respectively, for the Fe(3)O(4)-SiO(2) 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 (Fe(3)O(4)-SiO(2)). From the results of the [Formula: see text] ([Formula: see text]) 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.