Magnetic properties of Fe/sub 3/O/sub 4/ nanoparticles encapsulated with poly(D,L lactide-Co-glycolide)

We have investigated the magnetic properties of Fe/sub 3/O/sub 4/ nanoparticles encapsulated with poly(D,L lactide-Co-glycolide) (PLGA) prepared by an emulsification-diffusion technique. The size of nanoparticles was reduced down to 90 nm through the optimization of the preparation condition such as homogenizer and agitator speed. Zero-field-cooled (ZFC)/field-cooled (FC) magnetization, magnetic hysteresis, and relaxation measurement were performed using a superconducting quantum interference device (SQUID) magnetometer from 5 K to 300 K to investigate the magnetic properties of nanoparticles. The SQUID measurements show superparamagnetism of nanoparticles with a blocking temperature of 120 K. By measuring the magnetic relaxation of the magnetization at 5 K, we obtained magnetic viscosity of PLGA-encapsulated Fe/sub 3/O/sub 4/ nanoparticles.