Soft magnetic nanocomposites for high-frequency and high-temperature applications

A survey of soft magnetic nanocomposites will be given laying emphasis on different methods and technologies to increase the frequency and high working temperature limit. The eddy current limited frequency range can be enhanced by reducing the initial permeability and sample thickness and by increasing the electrical resistivity. Selecting high Curie temperature components and hereby increasing the decoupling temperature can raise the working temperature. For metal–metal type nanocrystalline alloys (known as Finemet and Nanoperm) the effective permeability is reduced by transversal induced anisotropies applying nanocrystalizing heat treatments under magnetic field or mechanical stress. The stress annealed Finemet (with effective permeability as low as 200) was found to be suitable for applications up to 250 °C and 400 kHz. The magnetic field annealing induces comparable high transversal anisotropy in Co doped Finemet only. The newly developed Fe–Fe oxide type electrodeposited multilayers and plasma sprayed bulk amorphous +ZrO composites are promising materials for surface mounted inductive elements applicable up to 1 MHz.