CORRELATION BETWEEN MAGNETIC AND MECHANICAL-PROPERTIES OF MOLDED IRONPARTICLE CORES

In order to optimize the molding conditions of polyimide bound iron pa rticle cores, it is necessary to understand the combined effects of te mperature and pressure on the mechanical and magnetic properties. In t he present study the major core specimens were molded at 250, 300, and 350 degrees C under 82, 102, and 129 MPa. To avoid the anisotropy due to the uniaxial pressure induced directional ordering, spherical iron particles were used. The results showed that the density, hardness, a nd rupture strength are generally increasing functions of molding pres sure and temperature, but the correlation is rather weak probably due to the presence of pores within the specimens. The maximum permeabilit y of these cores vary in a range 30-110. By annealing selected core sp ecimens at an elevated temperature, however, the maximum permeabilitie s increased to 900-1400 without noticeably changing the density. The m agnetization curves of the annealed specimens show unmistakable eviden ce of domain wall motion suggesting the formation of a network allowin g macroscopic propagation of domain walls. The results also indicate t hat the state of particle matrix interface may significantly contribut e to the overall magnetic properties of molded cores since annealing p articles alone is known to increase the maximum permeability by a fact or of 2-4. (C) 1997 American Institute of Physics.