Studies on the direct and converse magnetoelectric effects in laminated composites

Abstract

The direct magnetoelectric effect is an electric polarization response of a material to an applied magnetic field, while the converse magnetoelectric effect is a magnetization response of a material to an applied electric field. Importantly, the direct and converse magnetoelectric effects can realize power-free magnetic field sensing devices and core-free magnetic flux control devices, respectively. In the past decades, a great deal of research efforts has been devoted to the direct magnetoelectric effect, first in single-phase materials, then in two-phase bulk composites, and lately in two-/three-phase laminated composites. To date, it is generally known that laminated composites of magnetostrictive and piezoelectric materials have superior direct magnetoelectric effect owing to their greater product effect of the magnetostrictive and piezoelectric effects. Among them, the ones formed by giant magnetostrictive alloy TbxDy1-xFe2-y (Terfenol-D) and piezoelectric single crystal (l-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) possess the best-performed direct magnetoelectric voltage coefficient (av), defined by a change in electric voltage in response to an applied ac magnetic field (dV/dH). However, few of reports have been made on the converse magnetoelectric effect in the composites, especially when the effect is to be qualitatively described by the converse magnetoelectric flux coefficient (aB), defined by a change in magnetic flux density in response to an applied ac voltage (dB/dV). Moreover, it is of great interest to obtain a physical correlation between the two effects in the same composites. Therefore, the present work is aimed to study the coexistence of the two effects in four distinct types of two-/three-phase laminated composites, with a focus on developing composites showing high magnetoelectric figure-of-merits (FOM ME), defined by the product of av and aB, for power-free magnetic field sensing and core-free magnetic flux control applications. Two representative types of magnetostrictive-piezoelectric laminated composites and two promising types of magnet-piezoelectric laminated composites have been developed and studied. They include: (1) two-phase laminates with a thickness-polarized PMN-PT plate sandwiched between two length-magnetized Terfenol-D plates (denoted as MPM laminates); (2) two-phase laminates with a length-magnetized Terfenol-D plate sandwiched between two thickness-polarized, electro-parallel-connected PMN-PT plates (denoted as PMP laminates); (3) two-phase laminates with a thickness-polarized PMN-PT disk sandwiched between two thickness-magnetized samarium cobalt (SmCo) disks (denoted as MagPMag laminates); and (4) three-phase laminates with a thickness-polarized PMN-PT disk sandwiched between two truncated conical titanium (Ti) caps and two thickness-magnetized SmCo disks (denoted as MagCPCMag laminates). To facilitate the development of the proposed laminates, the material properties of the three constituent functional phases: namely, Terfenol-D (Tb0.3Dy0.7Fe1.92), PMN-PT [0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3], and SmCo (SmCo5), have been evaluated. Physical models for predicting the quasistatic av and aB in each of the four types of laminates under different combinations of dimensions and material properties have been refined or developed. FOMME has been adopted to provide a quantitative measure of the simultaneously high av and aB in a given laminate. The MPM and PMP laminates have been fabricated with dimensions of 12 mm (length) x 6 mm (width) x t (thickness), where t = mtM +ptp', m and p are the number of magnetostrictive and piezoelectric plates, respectively; and tp = 1 mm. The quasistatic and dynamic characteristics of the laminates have been measured, and the quasistatic properties have been compared with those predicted by the physical models. The MagPMag and MagCPCMag laminates, having radius 5 mm and thickness l = 2(tMag + tCh + tC) + tp, where tMag is the thickness of the SmCo disk; tCh is the cavity height of the Ti cap; tC is the thickness of the Ti sheet; and tp = 0.6 mm, have also been fabricated, characterized, and compared with the physical model predictions. Practical implications of the modeled and measured results for power-free magnetic field sensing and core-free magnetic flux control devices have been included.