Effect of low magnetic field heat treatment process on grain sizes and soft magnetic properties of Finemet cores

In this study, we investigate the effect of low transverse magnetic field annealing on the soft magnetic properties of cores made of industrial Finemet ribbons. The variation of static/dynamic magnetic properties and average grain size of the cores obtained by zero-field annealing (ZFA), secondary-field annealing (SMA) and direct-field annealing (DMA) are studied in detail. It is found that the average grain size obtained by DMA decreased compared to that of the ZFA sample, while the average grain size increased slightly after SMA. The effective permeability (& mu;e) of the ZFA sample after SMA decrease less than that of the ZFA sample with increasing frequency. The & mu;e of the DMA sample decreases significantly at the low-frequency stage but tends to decrease smoothly overall, maintaining high effectiveness at high frequencies magnetic permeability. For example, at 100 kHz, the & mu;e of ZFA at 550 degrees C temperature is only 0.6 x 104, while the & mu;e of SMA and DMA are 2.0 x 104 and 2.2 x 104, respectively. Meanwhile, the Hc = 1.85 A/m, Br = 0.59 T after ZFA and Hc = 1.67 A/m after DMA show no significant decrease compared to ZFA. While Hc = 0.55 A/m, Br = 0.08 T after SMA. Due to the field anisotropy constant Ku generated after SMA and DMA, the average anisotropy constant is dominated by Ku, the domain structure becomes simple and uniform, and the domain width becomes larger. This leads to a decrease in core losses with increasing frequency and improves the high-frequency characteristics of the core. These results can provide good guidance for performance optimization for Finemet alloys in a wide frequency range.

Automated summary

In this study, the effect of low transverse magnetic field annealing on the soft magnetic properties of Finemet ribbons cores was investigated. The static/dynamic magnetic properties and average grain size of cores obtained by zero-field annealing, secondary-field annealing, and direct-field annealing were studied. It was found that secondary-field annealing resulted in an increase in average grain size and effective permeability, leading to improved high-frequency characteristics.