A Self-Biased Strontium Ferrite-Nickel Ferrite Compostite and PZT Bilayer for Magnetic Field Sensors

Magnetoelectric (ME) composites are promising materials for use as magnetic sensors and arrays for applications such as medical imaging. The search for ME composites with high sensitivity and self-magnetic-biasing to eliminate the need for external bias is in progress for several years. Here we report on a novel approach to obtain strong ME coupling without the need for a dc magnetic field. We have used a bilayer composite obtained by attaching vendor supplied PZT and a piezomagnetic composite comprising of M-type Sr-ferrite, a hard ferrite, and spinel NiFe204, a soft ferrite. We carried out a systematic study of structural, compositional, magnetic and magnetostrictive properties of the synthesized ferrite composites at room temperature. We use the lock-in technique to measure ME voltage coefficient of the bilayer composites formed by the ferrite composites and PZT shows a value of ~26 mV/cmOe at room temperature. We attribute the zero-bias ME strengths to the large bias provided by the magneto-crystalline anisotropy associated with the ferrite composites.