Magnetic nanocomposite materials for high temperature applications

Magnetic nanocomposites comprised of nano-sized magnetic crystals embedded in an amorphous matrix have been shown to have excellent soft magnetic properties. In particular, amorphous and nanocrystalline materials have been investigated for various soft magnetic applications including transformers and inductive devices. The historical development of nanocomposite soft magnetic materials will be reviewed. In these materials it has been determined that an important averaging of the magnetocrystalline anisotropy over many grains coupled within an exchange length is at the root of the magnetic softness of these materials. The crystallization kinetics and the chemical partitioning occurring during crystallization will be described. In particular, the role of the amorphous phase in exchange coupling magnetic nanoparticles at elevated temperatures will be discussed. In HITPERM nanocomposites, developed by our group, nanocrystalline α and α"(B2)-FeCo are formed with significantly improved high temperature magnetic properties than in it\´s predecessors, NANOPERM and FINEMET. HITPERM has been developed for applications with high permeability requirements and with needs for large inductions at high temperatures. Recent work in characterizing the performance of HITPERM magnetic nanocomposite systems will be described. Specifically we have developed soft magnetic alloys that exhibit high magnetic induction at temperatures above current operating ranges for commercial devices. The applications for this material in high frequency (up to 1MHz) inductive devices for high temperature power electronics will be reviewed