Magnetoelectric dual-particulate composites with wasp-waisted magnetic response for broadband energy harvesting

Dual-particulate composites of cobalt ferrite dispersed in a fully dense PZT matrix are produced by quite-fast sintering of mechanically activated powders. By high-energy milling of the powders a bi-modal grain size distribution, with octahedral nano-grains and larger grains grown by multiple parallel twinning, are achieved in the final microstructure. The material display a “wasp-waisted” magnetic response as a consequence of the two main CoFe2O4 grain populations and can be exploited for broadband energy harvesting or field sensors. After poling under 5 kV/mm, a maximum d33 of 30 pC/N was achieved. This value is an order of magnitude lower than that of bulk PZT. Nevertheless, a magnetoelectric coefficient of 1.74 mV cm−1 Oe−1 is obtained, which suggests the high potentiality of these materials, since this value is higher than that shown by magnetoelectric composites with similar composition and connectivity reported in literature. This is so for a partially poled material and thus, magnetoelectric coefficients should be significantly increased by improving the poling process.