Dynamic losses in nanocrystalline finemet for various annealing temperatures

Abstract

The influence of thermal treatments on the dynamical magnetic properties of finemet ribbons was investigated. The amorphous ribbons of composition Fe 73.5Cu 1Nb 3Si 13.5B 9 have been annealed at various temperatures. Above their crystallization temperature homogenous, nanocrystalline α-FeSi grains with grain diameter of 3–12 nm have been produced. The total energy loss density for frequencies from 20 Hz to 50 kHz and polarizations from 0.2 to 0.9 T was measured and subdivided into hysteresis loss and dynamic loss. For annealing temperatures from 500 to 580°C and 1 h annealing time a broad minimum in the hysteresis losses occurs and splitting up into two minima for high polarizations. The dynamic losses show deeper minima at nearly the same annealing temperatures. The total losses in the region of the broad minimum of the hysteresis losses are mainly determined by the dynamic losses. For annealing temperatures over 590°C the total losses are mainly determined by the hysteresis losses. For 0.2 T polarization amplitude and high frequencies the decrease of the anomaly factor with increasing frequency is extraordinarily high.