Dual-peak self-biased magnetoelectric couplings in symmetrical multiferroic heterostructures

Magnetoelectric (ME) couplings in multiferroic composites exhibiting simultaneous ferromagnetic and ferroelectric phases through strain-mediated interactions have attracted great interests for their promising technological applications on magnetic sensors, energy-harvesting devices, four-state memories and microwave resonators[1, 2]. Initially, the research on magnetoelectric materials focuses on the single-phase magnetoelectric effects (e.g. Cr 2 O 3 ) with low Curie temperature and weak magnetoelectric coefficients[3]. It has been reported that the ME composite consisting of magnetostrictive and piezoelectric phases exhibits much stronger ME coupling than that of the single-phase ME materials. To date, the highest ME coefficient with value of 1100V/cmOe has been reported in Metglas/PMN-PT ME composites by Gao et al[4]. For the purpose of provoking stronger piezomagnetic response, the higher ME coupling for the composite operating in L-T mode is acquired only at an additional magnetic bias of ∼400Oe[5]. Although much efforts have been devoted by some researchers to decreasing the required bias, it is still indispensable to improve the ME output[6]. Since the additional bias goes against the need for device fabrication and implementations, resulting in the decrease of the possible spatial resolution and the increase of the required space. Therefore, efforts of removing the required bias have been emphasized. In the last decade, self-biased ME response has attracted an ever-increasing focus and provoked a great number of research activities. For example, Mandal et al observed the phenomenon of self-biased ME coupling in a ME composite with compositionally grated ferrite due to a torque arising from a grading induced internal field in the ferrite[7]. Yang et al presented a methodology for achieving self-biasing by just changing the electrical connections of PZT plates in a three-phase ME composite of NKNLS-NZF/Ni/NKNLS-NZF[8]. Lage et al demonstrated a ME composite consisting of AlN and multilayers with the sequence of Ta/Cu/Mn 70 Ir 30 /Fe 50 Co 50 to provide exchanging bias in the device[9]. Furthermore, most investigations have been focused on the realization of the zero-biased ME coupling by using the difference of magnetic properties in two (or more) different epoxy-bond-ed magnetostrictive phases. In order to increase the induced non-zero ME voltage at zero bias, one could use an asymmetric bimorph structure consisting of piezoelectric layers placed between two distinct ferromagnetic layers to realize the self-biased ME effects at two resonance frequency. Recently, Chen et al reported self-biased ME effect and dual-peak ME effects in various three-phase laminate composites of FeCuNbSiB/Terfenol-D/PZT (FeMP), FeCuNbSiB/iron-nick-el-based ferromagnetic alloy with constant elasticity/PZT(FeFP) and FeCuNbSiB/Ni/PZT (FeNiP), both self-biased effect characterized by non-zero ME effect at zero bias and dual-peak ME effect have been observed[10]. However, to excite simultaneous bending and transverse oscillations in such a structure, rather complicated magnetic layers with magnetostriction in opposite directions are required, and the studies on the dual-peak resonance characteristics for realization of the self-biased ME effects in a symmetrical multiferroic heterostructure have been not reported yet.