Pulsed Magnetic Field Experiments in SMM and SMC Materials: New Questions About Its Properties and Applications

This article analyzes the magnetization rotation behavior of Fe-based soft magnetic materials and soft magnetic composites (SMMs and SMCs, respectively) samples. Room temperature measurements of the complex permeability until frequencies near 20 MHz and isothermal M(H) magnetization curves obtained from room to low temperatures (down to 20 K) show very similar soft magnetic behavior for both type of samples. Pulsed magnetic fields have been used to test their behavior under extreme conditions. Even with a substantial increase of the field variation sweeping rate and the temperature reduction (from 20 to 300 K) both types of materials keep their pronounced non-hysteretic behavior. However, zero field cooled-field cooled (ZFC-FC) curves with an applied field lower than 7.5 kOe show full irreversibility below room temperature, which indicates the existence of a broad distribution of barrier heights and seems to be in full contradiction with the obtained complex permeability and M(H) results. In this article, we aim to clarify this new and unexpected dual behavior. We suggest the existence of pinning barrier heights which are very sensitive to the variation of the magnetic field allowing the magnetization rotation with no losses while there are other barrier heights which need high values for the magnetic static fields to be removed when the temperature changes.