Significant magnetoelectric enhancement of composite films of CoZnxFe2-xO4 particles and poly (vinylidene fluoride-trifluoroethylene) for AC magnetic sensors

Polymer-based magnetoelectric (ME) nanocomposites exhibit a low ME effect and high bias field at room temperature, which severely limits their application in flexible wearable sensors. To overcome these obstacles, Zn-doped magnetic nanoparticles of CoZn_xFe_2-xO₄ (x = 0, 0.1, 0.2, and 0.3) were prepared by an auto-combustion method in this work. The obtained magnetostrictive curves imply that Zn element doping can improve greatly the piezomagnetic coefficient of magnetic nanoparticles, and among the tested materials, CoZn_0.1Fe_1.9O₄ has the largest piezomagnetic coefficient. Composite films of poly(vinylidene fluoride-trifluoroethylene) and CoZn_0.1Fe_1.9O₄ (P(VDF-TrFE)/CoZn_0.1Fe_1.9O₄) were prepared by spin coating. The maximum ME voltage coefficient of P(VDF-TrFE)/CoZn_0.1Fe_1.9O₄ composite film with a filler weight concentration of 10 wt% is 87.9 mV cm⁻¹ Oe⁻¹ with a bias field of 1050 Oe and a resonance frequency of 46 kHz, which is the highest value reported in the literature of 0–3 type polymer-based ME composite films at present. To evaluate the composite films for application in magnetic sensors, the ME output voltage was measured at a bias field of 1050 Oe with increasing AC magnetic field, demonstrating a good linear relationship with linearity of 0.999. These results indicate that the piezomagnetic coefficient of magnetic materials is an the important factor for the great enhancement of the ME voltage coefficient. This work provides a new approach for the synthesis of more effective polymer-based ME nanocomposites for potential applications in smart wearables.     

Oxygen octahedra distortion-induced multiferroic properties of Er and Zr co-doped BiFeO3 nanoparticles

The present work unveiled the distortion of oxygen octahedra influencing magnetic and magnetoelectric properties of novel Bi_1−xEr_xFe_1−yZr_yO₃ (x = 0, .05, .1, y = .02, .05) polycrystalline nanoparticles by sol–gel route. X-ray diffraction patterns analysis reveals that pristine BiFeO₃ and doped BiFeO₃ are crystalized in the rhombohedral structure (R3c). The Fe–O–Fe bond angle of Bi_1−xEr_xFe_1−yZr_yO₃ (x = 0, .05, .1, y = .02, .05) varies between 141° and 159.62° as the concentration of Er (via Bi site) and Zr (via Fe site) ions increases in BiFeO₃. As a result, the tilt angle of oxygen octahedra and the canting angle of spiral spin arrangement increase. Hence, the maximum magnetization varies between .03144 and .37558 emu/g in Er and Zr co-doped BiFeO₃ system. The number of electrons per unit cell of Bi_1−xEr_xFe_1−yZr_yO₃ (x = 0, .05, .1, y = .02, .05) lies between 733.38 and 831, respectively. Further, the number of coherently diffracting domains increases from 3.07 to 5.21, and then it decreases when Er and Zr are increased in BiFeO₃. Consequently, the magnetoelectric coupling coefficient varies between .0265 and .2511 mV/cm Oe, respectively. Particularly, Bi_0.95Er_0.05Fe_0.98Zr_0.02O₃ shows enhanced magnetic and magnetoelectric behaviors compared to other samples.