Dispersion characteristics for low-frequency magnetoelectric coefficients in bulk ferrite-piezoelectric composites

Ferrite-piezoelectric composites are magnetoelectric (ME) due to the interaction between magnetic and electrical subsystems through mechanical forces. A theory for the low-frequency Maxwell–Wagner relaxation in ME coefficients is discussed for bulk composites of nickel or cobalt ferrite and lead zirconate titanate (PZT). ME coefficients versus frequency spectra show two types of relaxation, over 0.1–100 μHz and 1–1000 Hz. The relaxation frequencies and the magnitude of the ME coefficients are dependent on the electrical and composite parameters and volume fraction for the two phases. The ME coefficient αEαE is in the range 10−1–104 mV/cm Oe, higher in cobalt ferrite–PZT than for nickel ferrite–PZT, and is strongly dependent on PZT volume fraction vv. Estimates of αEαE and relaxation frequencies versus vv provided here are useful for engineering composites with maximum ME effects for specific frequency bands.