Magnetization-graded multiferroic composite and magnetoelectric effects at zero bias

Abstract

A magnetoelectric (ME) phenomenon in a multiferroic composite consisting of magnetization-graded ferromagnetic and ferroelectric phases is discussed. The traditional strain mediated coupling in such composites arises due to magnetostriction and piezoelectric effects associated with the ferroic phases. Such an ME effect, in general, requires a bias magnetic field ${H}_{0}$ and an ac magnetic field. This paper is on the observation and theory of ME interactions under zero bias (${H}_{0}$ $=$ 0) in a bilayer of lead zirconate titanate (PZT) and a ferromagnetic layer in which the magnetization is graded with the use of Ni and Metglas. At low frequencies, the ME coefficient ranges from 0.3 to 1.6 V/cm Oe and depends on the thickness of the Metglas. A similar dependence is also observed for the ME coupling at bending modes. A factor of 40 increase in the ME voltage is measured at resonance. The zero-bias ME coupling is attributed to strain-mediated coupling between the transverse magnetization due to magnetization grading at the interface of Ni-Metglas and the in-plane ac magnetic field. Theoretical estimates of ME coefficients at low frequencies and bending modes are in general agreement with the data.