Fine particle magnetic properties and microstructures of nanocrystalline Fe-Cu-Nb-Si-B alloy at elevated temperatures

Magnetic behavior in nanocrystalline Fe72Cu1Nb4.5Si13.5B9 alloy is investigated by measurements of low and high field magnetization and coercivity over the temperature range from 300 K to 800 K. When the measuring temperatures approach the Curie temperature of intergranular amorphous phase Tc(amorphous), the nanocrystalline materials consist of ferromagnetic Fe-rich nanocrystals embedded in a weakly magnetic or non-magnetic matrix. Samples with different volume fractions of crystalline phase are prepared to investigate the nature and strength of inter-particle interactions between the nanocrystallites. It is shown that at temperatures above Tc(amorphous), the specimens with low fraction of nanocrystalline particles exhibit superparamagnetic behavior. In the case of specimens with increasing volume fraction of crystalline phase, the magnetic interaction between particles suppresses superparamagnetic fluctuations and superferromagnetic ordering of the particle magnetic moments above Tc(amorphous) is observed.