Coupled magnetic-electric properties and critical behavior in multiferroic particulate composites

We report on a systematic experimental investigation of a class of multiferroic, three-phase particulate composite of Tb-Dy-Fe alloy, lead-zirconate-titanate (PZT), and polymer, in which a small volume fraction f of Tb-Dy-Fe alloy particles without and with the particle surfaces modified by an inactive surfactant are dispersed in PZT/polymer mixture. The measured electrical properties demonstrate that a percolation transition occurs in the three-phase composite as in normal two-phase metal-insulator continuum media. Our piezoelectric measurements also show a percolation transition which provides an experimental test of the critical behavior of the piezoelectric composites with conductive fillers in the percolation regime. Accordingly, the multiferroic composite exhibits increasing magnetoelectric response in the low f range, but such magnetoelectric response sharply drops when f approaches the percolation threshold above which the composite becomes a conductive, magnetostrictive composite only. The inactive interface between the alloy particles and the PZT/polymer matrix induced by coating surfactant on the alloy particles produces a negative effect on the piezo- and magnetoelectric properties of the composite. (C) 2003 American Institute of Physics.