Magnetic coupling induced increase in the blocking temperature of gamma-Fe2O3 nanoparticles

In this article, we report the magnetic properties of surfactant coated gam ma-Fe2O3 nanoparticles which are pressed under different pressures. With in creasing pressure, the sample volume decreases, density increases, and a 55 % density change has been achieved. The blocking temperature is increased f rom 50 to 80 K. Analyzing the data of blocking temperature versus densities , which exhibits linear relationship, and comparing the magnetic properties , the increase in blocking temperature is understood in terms of increased magnetic interactions between neighboring nanoparticles, which is due to th e reduced average interparticle distance by the applied pressure. (C) 2000 American Institute of Physics. [S0021-8979(00)06410-0].