In contrast to typical magnetic energy generators that use electromagnetic induction, which are bulky and have low generation efficiency under small magnetic fields at low frequency, magneto-mechano-electric (MME) generators utilizing the magnetoelectric (ME) coupling effect and magnetic interactions are considered promising candidates. MME generators will serve as a ubiquitous autonomous energy source converting stray magnetic noise to useful electric energy for applications in wireless sensor networks (WSN) for the Internet of Things (IoT) and low-power-consuming electronics. The key component in a MME generator is the ME composite consisting of piezoelectric and magnetostrictive materials, which elastically couples the electric and magnetic behaviour of the respective constituent. Here, we report a MME generator consisting of a crystallographically oriented Pb(Mg_1/3Nb_2/3)O₃–Pb(Zr,Ti)O₃ piezoelectric single crystal macro-fibre composite and a highly textured magnetostrictive Fe–Ga alloy, which exhibits an exceptionally high rectified DC output power density of 3.22 mW cm⁻³. The large energy generation in this structure is ascribed to the coupling between the strong anisotropic properties of the piezoelectric single crystal fibres and textured Fe–Ga magnetostrictive alloy. A smart watch with IoT sensors was driven by the MME generator under a 700 μT magnetic field.

Single crystal samples of quenched ${\mathrm{Fe}}_{81.3}{\mathrm{Ga}}_{18.7}$ and of slow cooled ${\mathrm{Fe}}_{81.3}{\mathrm{Ga}}_{18.6}{\mathrm{C}}_{0.08}$ exhibit magnetostriction of $\sim 400\mathrm{ppm}$ . However, they also exhibit a sufficiently high permeability that eddy currents, which form in proportion to sample thickness, limit their operation at high frequencies. During attempts to roll thin sheets of ${\mathrm{Fe}}_{81.3}{\mathrm{Ga}}_{18.7}$ and carbon-added ${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$ alloys, cracks formed along grain boundaries and subsequently samples fractured during hot rolling such that the alloy was too brittle to make thin sheets. In this paper, the influence of alloying additions of B, Mn, Mo, Nb, and NbC on the deformation behavior and magnetostriction of Fe–Ga alloy was investigated. These alloying additions except Mn improved the roll ability and provided a high quality finished rolled sheets with thickness ranging from $0.18\text{to}0.35\mathrm{mm}$ . Results are shown to demonstrate that the fracture mode of 1.0% Mo- or 0.5% B-added ${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$ alloy was changed from an intergranular to a transgranular fracture mode with cleavage. Annealed sheets with additions of 0.5% B, 1.0% B, 0.5% Mo, 2.0% Mo, 0.5% Nb, and 1.0% NbC exhibited the maximum magnetostrictions of 103, 160, 127, 88, 121, and $183\mathrm{ppm}$ , respectively. Electron backscattering diffraction (EBSD) analysis showed texture in the 1.0% B-added sheet changed from $\gamma$ -fiber texture (as rolled) to the Goss texture {110}⟨001⟩ (annealed).

High-entropy alloys (HEAs) containing multiple principle alloying elements exhibit unique properties so they are currently receiving great attention for developing innovative alloy designs. In FeCoNi-based HEAs, magnetic behaviors strongly depend on the addition of alloying elements, usually accompanied by structural changes. In this work, the effect of non-magnetic components on the ferromagnetic transition and magnetic behaviors in equiatomic FeCoNiCrX (X=Al, Ga, Mn and Sn) HEAs was investigated. Alloy ingots of nominal compositions of HEAs were prepared by arc melting and the button ingots were cut into discs for magnetic measurements as functions of magnetic field and temperature. The HEAs of FeCoNiCrMn and FeCoNiCrSn show typical paramagnetic behaviors, composed of solid solution FCC matrix, while the additions of Ga and Al in FeCoNiCr exhibit ferromagnetic behaviors, along with the coexistence of FCC and BCC phases due to spinodal decomposition. The partial phase transition in both HEAs with the additions of Ga and Al would enhance ferromagnetic properties due to the addition of the BCC phase. The saturation magnetization for the base alloy FeCoNiCr is 0.5 emu/g at the applied field of 20 kOe (T_C = 104 K). For the HEAs of FeCoNiCrGa and FeCoNiCrAl, the saturation magnetization significantly increased to 38 emu/g (T_C = 703 K) and 25 emu/g (T_C = 277 K), respectively. To evaluate the possibility of solid solution FCC and BCC phases in FeCoNiCr-type HEAs, we introduced a parameter of valence electron concentration (VEC). The proposed rule for solid solution formation by the VEC was matched with FeCoNiCr-type HEAs.