Effects of processing upon the properties of soft magnetic composites for low loss applications

We have investigated the effects of processing variables and methods on the density, structure and magnetic properties of soft magnetic composite (SMC) materials primarily for use in low loss applications. Two commercially available SMC materials from Hoganas AB, Sweden were used throughout the study. The materials differed only in terms of the solid state lubricant incorporated in the powder. This was sufficient to affect the density of pressed samples. Both monotonic and cyclic pressing regimes were used to compact the materials, with pressures sufficiently large to control the bulk mechanical properties of the samples produced (Hardness typically 1.6 GPa). Samples were heat-treated to both relieve any stresses imposed during pressing, and to control the final composition through oxidation or non-oxidation processes. Magnetic properties were observed using a vibrating sample magnetometer and Barkhausen noise analyser and electrical properties determined using a micro-ohmmeter. Both magnetic and electrical properties were observed to be strongly dependent on sample density and heat treatment.