Theoretical consideration of experimental data of thermal and magnetic properties of polymer-bonded soft magnetic composites

Spherical iron silicon (FeSi) particles and irregular shaped magnetite (Fe3O4) particles with particle sizes <= 146 mu m and varying volume filler fractions up to x = 0.7 (70 vol%) were mixed with polypropylene (PP) matrix. The samples were prepared by kneading and injection moulding and show particle-particle interaction at elevated filler fraction of x >= 0.5. Thermal and magnetic properties of the composites were characterized and show a significant increase at filler fractions of x >= 0.3. The thermal conductivity of PP (0.176 W/(m K)) was increased up to seven times to 1.239 W/(m K) at x = 0.7. FeSi-filled composites show slightly higher values of thermal conductivity than Fe3O4-filled composites. The magnetic permeability of the composites rise from 1 for PP to a maximum value of 23.1 for PP/FeSi composites at x = 0.7. The nonlinear increase in the thermal conductivity corresponds with the lower boundary of the Hashin-Shtrikman model. The Bruggeman model can be applied to describe the nonlinear increase in the magnetic permeability. Magnetic permeability increases with mean particle diameter as well as magnetic coercivity and loss dissipation increases with inverse mean particle diameter.