Intergranular Phase in Nanocrystalline Alloys: Structural Aspects and Magnetic Properties

Abstract

The nanocrystalline alloys consist of nanocrystalline grains embedded in a residual amorphous phase. Such a structure provides excellent soft magnetic properties, as evidenced in FINEMET, NANOPERM, and HITPERM systems. Apart from recognizing the important role of nanocrystalline grains governing these soft magnetic properties, we focused our attention on the amorphous remainder which shows heterogeneous chemical composition and structure, thus influencing the magnetic interactions between nanocrystalline grains. The magnetically ordered structure giving rise to excellent soft behaviour is best generated by ferromagnetic intergranular phase at low temperature. At high temperatures, it causes degradation of soft magnetic properties with the occurrence of superparamagnetic fluctuations at a low crystalline volumetric fraction. On the contrary, for a high crystalline fraction, a rather narrow intergranular phase is polarized by the interactions between ferromagnetic crystalline grains which increase its Curie temperature.