Superspin Glass State in Mgfe2o4 Nanoparticles.

MgFe 2 O 4 nanoparticles were prepared at different annealing temperature of 400, 450 and 500 °C. Transmission electron microscope image show that powders consist of ∼ 8 nm particles. Scanning electron microscope image show aggregation of particles and formation of large particles with size of 20-100 nm. Obtained nanoparticles were superparamagnetic at room temperature. A broad peak (T P ) was observed in temperature dependant AC magnetic susceptibility curves. The T P increased by increasing the annealing temperature, as a result of increase in particles size. The effective anisotropy constant estimated about 2 (to 3) × 10 5 erg/cm 3 . The aggregation caused high interparticles interactions and consequently the total energy barrier between equilibrium states increased. Analysis of frequency dependence AC magnetic susceptibility showed presence of superspin glass state at low temperatures. [ABSTRACT FROM AUTHOR]