Enhancement of the magnetoelectric effect in multiferroic CoFe$_2$O$_4$/PZT bilayer by induced uniaxial magnetic anisotropy

TL;DR

This study demonstrates that inducing uniaxial magnetic anisotropy in cobalt ferrite via Spark Plasma Sintering significantly enhances the magnetoelectric effect in CoFe₂O₄/PZT bilayer composites, with potential for improved device performance.

Contribution

It introduces a method to induce uniaxial magnetic anisotropy in cobalt ferrite, leading to a threefold increase in the magnetoelectric coefficient in bilayer composites.

Findings

Anisotropic cobalt ferrite shows higher longitudinal magnetostriction.

Anisotropic cobalt ferrite exhibits increased magnetoelectric coefficient.

Resonant frequency excitation further enhances the ME effect.

Abstract

In this study we have compared magnetic, magnetostrictive and piezomagnetic properties of isotropic and anisotropic cobalt ferrite pellets. The isotropic sample was prepared by the ceramic method while the sample exhibiting uniaxial anisotropy was made by reactive sintering using Spark Plasma Sintering (SPS). This technique permits to induce a magnetic anisotropy in cobalt ferrite in the direction of the applied pressure during SPS process. Sample with uniaxial anisotropy revealed a higher longitudinal magnetostriction and piezomagnetism compared to the isotropic sample, but the transversal magnetostriction and piezomagnetism were dramatically reduced. In the case of magnetoelectric layered composite, the magnetoelectric coefficient is directly related to the sum of the longitudinal and transversal piezomagnetic coefficients. These two coefficients being opposite in sign, the use of material exhibiting high longitudinal and low transversal piezomagnetic coefficient (or vice versa) in ME devices is expected to improve the ME effect. Hence, ME bilayer devices were made using isotropic and anisotropic cobalt ferrite stuck with a PZT layer. ME measurements at low frequencies revealed that bilayer with anisotropic cobalt ferrite exhibits a ME coefficient three times higher than a bilayer with isotropic cobalt ferrite. We also investigated the behavior of such composites when excited at resonant frequency.