Zero-biased magnetoelectric effects in five-phase laminate composites with FeCoV soft magnetic alloy

Magnetoelectric (ME) response has attracted continuously increasing interest in the past decades due to its potential applications in many new multifunctional devices, including magnetic storage, magnetic sensors, current sensors, and energy harvesters.^[1] In general, single-phase ME materials are difficult to be utilized in such devices because the ME responses are weak and mostly appear at low temperature. Compared to single-phase ME materials, Magnetoelectric composites consisting of piezoelectric materials (e.g., PZT and PMN-PT) and magnetostrictive materials (e.g., Terfenol-D and Metglas) exhibit strong ME responses at room temperature, and meet the demands of practical application. However, in order to obtain high piezomagnetic coefficient and ME response, most of the reported ME composites require an external bias magnetic field (H_bias) that increases their sizes and costs.[^2] To overcome these limitations, more and more researchers have focused on zero-biased ME effects in the composites. Recently, some studies have attempted to achieve high zero-biasd ME response with different methods. For example, Mandal et al. have reported that ME composite of PZT and graded NZFO show an enhancement in the ME coefficient at zero bias. ^[3]Yang et al. demonstrated a methodology for achieving zero-biased ME response by changing the electrical connections in a sandwiched ME structure of NKNLS-NZF/Ni/NKNLS-NZF. These methods are difficult to realize and require special synthesis process. In fact, utilizing an internal magnetic bias of the magnetostrictive materials in ME composite is a feasible way to solve thisproblem. In this paper, a new zero-biased five-phase laminate composite consists of FeCoV/Terfenol-D/Pb(Zr₁-_x, Ti_x)O₃(PZT)/Terfenol-D/FeCoV (FMPMF) is presented, whose magnetoelectric (ME) coupling characteristics have been investigated. Due to the different magnetic characteristi- s between FeCoV and Terfenol-D (such as permeability, saturation magnetization and magnetostriction), an internal magnetic field is formed in the compound magnetostrictive layers. It is found that the resonant ME voltage coefficient of five-phase laminate composite is much larger than that of traditional Terfe-nol-D/PZT/Terfenol-D (MPM) laminate composite at zero bias. The experimental results show that the zero-biased resonant ME voltage coefficient strongly depends on the thickness of FeCoV layers as shown in Fig.1. When the thickness of FeCoV layers is 90μm, we obtain the optimum resonant ME voltage cofficient of 1.96 V/Oe at the zero magnetic bias field, which is 1.75 times as great as that of MPM laminate composite. Furthermore, a low-frequency ME voltage coefficient of 50.4 mV/Oe is achieved, which is 2.1 times higher than that of the MPM laminate composite. Meanwhile, the induced zero-bias ME voltage of FMPMF laminate composite shows an excellent linear relationship to ac magnetic field both at the low frequency (1kHz) and the resonant frequency (115.14kHz) as shown in Fig.2. It indicates that the proposed zero-biased five-phase laminate composite shows promising applications for high sensitive dc magnetic field sensors, zero-biased ME transducers and small-size energy harvesters.