Pressure effects on gamma-Fe2O3 nanoparticles.

The effects of pressure on the gamma-Fe2O3 nanoparticles with the diameter of 6.5 nm were investigated through the DC magnetic measurements up to P = 13.7 kbar. The superparamagnetic blocking phenomenon, detected from zero field cooled-field cooled (ZFC-FC) magnetic behavior, exhibits a characteristic pressure dependence: The initial pressure makes the irreversible temperature region reduced, whereas at around P 4 kbar, it turns to be expanded. The shift of the hysteresis loop by FC process also shows similar pressure dependence. This gamma-Fe2O3 nanoparticle has instable surface contributions to the net moment, which may be quite sensitive to external stress. The effect of some stress on the surface may result in changing the magnetic moment of the core. (C) 2006 Elsevier B.V. All rights reserved.