Commercial soft magnetic cores used in power electronics are limited by core loss and decreased ferromagnetism at high temperatures. Extending functional performance to high temperatures enables increased power density in electric systems with fixed power output and elevated operating temperature.
NASA Glenn Research Center developed a novel nanocomposite soft magnetic material for use in power electronics. The material maintains near-room-temperature attributes of available soft magnetics while surpassing these materials in temperature capability. In the present state-of-the-art, soft magnetic nanocomposites have an upper temperature limit rating of 150 °C before core loss occurs. By adjusting the composition and fabrication, the operating temperature range was increased to 400 °C with minimal increase in core loss.
Nanocomposite soft magnetic materials are typically comprised of a combination of raw materials including iron, silicon, niobium, boron, and copper. Instead of niobium, the new material utilizes small cobalt and tantalum additions. The raw materials are combined to form an amorphous precursor through melt spinning. The novelty with the fabrication lies in the thermal annealing step, which nucleates and crystallizes the precursor to form the composite structure of the material. By adjusting the temperature and magnetic field of the thermal annealing step, the process results in good coupling between the crystalline and amorphous matrix phases.
While operating at high temperatures, the material exhibits high permeability and saturation flux density desirable in soft magnetics. The material expands the application of soft magnetic material, enabling efficient power electronics that are smaller and lighter due to the reduced need for cooling.