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 (M(T)) and the time dependence of magnetization (M(t)), using the SQUID magnetometer measurement. The M(T) 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 (C), effective magnetic moment (μeff), and Weiss temperature (θP) are 4.2 (emu.K.Oe/mol), 5.77 μB, and -349 K, respectively, for the Fe 3 O 4 samples, and 81.3 (emu.K.Oe/mol), 25.49 μB, 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 M(t) 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.