Among the magnetostrictive alloys, the one formed of iron and gallium (called “Galfenol” from its U.S. Office of Naval Research discoverers in the late 1990s) is attractive for its low hysteresis, good tensile stress, good machinability, and its rare-earth-free composition. One of its applications is its association with a piezoelectric material to form an extrinsic multiferroic composite as an alternative to the rare room-temperature intrinsic multiferroics such as ${\mathrm{Bi}\mathrm{Fe}\mathrm{O}}_3$. This study focuses on thin ${\mathrm{Fe}}_{0.81}{\mathrm{Ga}}_{0.19}$ films of thickness 5, 10, 20, and 60 nm deposited by sputtering onto glass substrates under a deposition field $H_{\mathrm{dep}}\sim 300$ Oe. Magnetization reversal study reveals a well-defined symmetry with two principal directions independent of the thickness. The magnetic signature of this magnetic anisotropy decreases with increasing ${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$ thickness due to an increase of the nonpreferential polycrystalline arrangement, as revealed by transmission electron microscopy (TEM) observations. Thus, when magnetic field is applied along these specific nontrivial directions, magnetization reversal is mainly coherent for the thinnest sample, as seen from the transverse magnetization cycles. The magnetostriction coefficient reaches 20 ppm for the 5-nm film and decreases for thicker samples, where the polycrystalline part with nonpreferential orientation prevails.

Magnetoelectric composites are an important class of multiferroic materials that are paving the way towards a new generation of multifunctional devices directly integrable into data-storage technology and spintronics. This study focuses on strain-mediated electrical manipulation of magnetization in an extrinsic multiferroic. The composite used includes 5- or 60-nm ${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$ thin films coupled to a piezoelectric (011) $\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_3$-$\mathrm{Pb}({\mathrm{Zr}}_x{\mathrm{Ti}}_{1-x}){\mathrm{O}}_3$ (PMN-PZT) material. A magnetization-reversal study reveals a converse magnetoelectric coefficient ${\alpha }_{\mathrm{CME},max}\approx 2.7\times {10}^{-6}\mathrm{s}{\mathrm{m}}^{-1}$ at room temperature. This reported value of ${\alpha }_{\mathrm{CME}}$ is among the highest so far, compared with previous reports on single-phase multiferroics and on composites. An angular dependence of ${\alpha }_{\mathrm{CME}}$ is also shown, arising from the intrinsic magnetic anisotropy of $\mathrm{Fe}\text{−}\mathrm{Ga}$. The highly efficient magnetoelectric composite $\mathrm{Fe}\text{−}\mathrm{Ga}$/PMN-PZT demonstrates drastic modifications of the in-plane magnetic anisotropy, with an almost ${90}^{\circ }$ rotation of the preferential anisotropy axis in thinner films under an electric field $E=10.8\mathrm{kV}{\mathrm{cm}}^{-1}$. Also, the influence of thermal strain on the bilayer’s magnetic coercivity is compared with that for a reference $\mathrm{Fe}\text{−}\mathrm{Ga}$/glass bilayer at cryogenic temperatures. A different evolution is observed as a function of temperature, revealing a thermomechanical influence of the substrate which has not yet been reported in $\mathrm{Fe}\text{−}\mathrm{Ga}$ thin films coupled to a piezoelectric material.

Mn substituted Mn_xZn_1−xCo₂O₄ (x = 0, 0.3, 0.5, 0.7, 1) oxides were synthesized by a facile co-precipitation method followed by calcination at 600 °C.