Dynamic Magnetostriction of CoFe2O4 and Its Role in Magnetoelectric Composites

Abstract

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 ∂λ=∂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=PbðZr; TiÞO 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/PbðZr; TiÞO 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.

Enhanced piezomagnetic coefficient of cobalt ferrite ceramics by Ga and Mn doping for magnetoelectric applications

“…It has been recently shown the strain derivative calculated from strain-field curves so obtained is not the appropriate parameter to describe dynamic deformation under alternate driving for semi-hard materials such as cobalt ferrite. 50 Instead, effective piezomagnetic coefficients directly obtained from dynamic magnetostriction measurements, which are consistently lower than quasistatic ones, must be used to calculate ME coefficients, as shown in Ref. 50.…”

“…50 Instead, effective piezomagnetic coefficients directly obtained from dynamic magnetostriction measurements, which are consistently lower than quasistatic ones, must be used to calculate ME coefficients, as shown in Ref. 50. Dynamic piezomagnetic coefficients can reach up to 70 % of the quasistatic ones under optimized ac and bias magnetic fields.…”

“…Dynamic piezomagnetic coefficients can reach up to 70 % of the quasistatic ones under optimized ac and bias magnetic fields. 50 Therefore, transverse ME coefficients α E 31 in this work were calculated using 70 % of the q 11 + q 21 data in Fig. 4.…”

Investigation of Piezomagnetism in Nickel Ferrite

“…However, for most of these applications, the key feature is not the static magnetostriction but the dynamic one, also known as piezomagnetic effect. Strictly speaking, the piezomagnetic coefficient is defined as the strain oscillation induced by an alternating magnetic field H AC at any bias field H DC [1], [7], [8], which can be written:…”

“…We have recently shown that this approximation may lead into quite relevant errors when evaluaiting ME devices performances particularly when semi-hard magnetostrictive materials (e.g. cobalt ferrites) are involved [8]. In fact, the strain derivative depends on the differential susceptibility χ dif f whereas the piezomagnetic effect arises from the dynamic susceptibility χ AC at any bias field.…”