Dynamic Magnetostriction of CoFe2O4 and Its Role in Magnetoelectric Composites

Applications of magnetostrictive materials commonly involve the use of the dynamic deformation, i.e., the piezomagnetic effect. Usually, this effect is described by the strain derivative partial derivative lambda/partial derivative H, which is deduced from the quasistatic magnetostrictive curve. However, the strain derivative might not be accurate to describe dynamic deformation in semihard materials as cobalt ferrite (CFO). To highlight this issue, dynamic magnetostriction measurements of cobalt ferrite are performed and compared with the strain derivative. The experiment shows that measured piezomagnetic coefficients are much lower than the strain derivative. To point out the direct application of this effect, low-frequency magnetoelectric (ME) measurements are also conducted on bilayers CFO/Pb(Zr, Ti)O-3. The experimental data are compared with calculated magnetoelectric coefficients which include a measured dynamic coefficient and result in very low relative error (< 5%), highlighting the relevance of using a piezomagnetic coefficient derived from dynamic magnetostriction instead of a strain derivative coefficient to model ME composites. The magnetoelectric effect is then measured for several amplitudes of the alternating field H-ac, and a nonlinear response is revealed. Based on these results, a trilayer CFO/Pb(Zr, Ti)O-3/CFO is made exhibiting a high magnetoelectric coefficient of 578 mV/A (approximately 460 mV/cm Oe) in an ac field of 38.2 kA/m (about 48 mT) at low frequency, which is 3 times higher than the measured value at 0.8 kA/m (approximately 1 mT). We discuss the viability of using semihard materials like cobalt ferrite for dynamic magnetostrictive applications such as the magnetoelectric effect.