The magnetoelectric effect of the CFO thin film by coupling a P(VDF- co -TrFE) piezoelectric layer

The CoFe₂O₄ (CFO) thin films are prepared by the sol-gel method combined with the spin-casting process, and the related SEM and XRD results show that a 9-layer spinning of the original sol together with an annealing temperature of 700 °C is the appropriate condition for obtaining this CFO film with an excellent magnetic performance. The CFO films are subsequently compounded with a ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-co-TrFE)]. After polarizing the obtained CFO/P(VDF-co-TrFE) double-layer composite film under a high electrical field of 275 MV/m, the P(VDF-co-TrFE) layer shows the character of normal ferroelectricity that has a large dielectric permittivity (ϵ₃₃/ϵ₀ = 9.5) and a high piezoelectric value (d₃₁ = 20 pC/N). Interestingly, we also find that the magnetization of this electrically poled CFO/P(VDF-co-TrFE) film increases from 85.58 to 99.15 emu/cm³ at a magnetic field of 1.8 T since the electrostrictive effect may lead to the re-orientation of magnetic domains and thereby resulting in a magnetization easy-axis reorientation effect in the out-of-plane direction of the CFO thin film. Consequently, a large magnetoelectric coupling coefficient (α_E31) of 508.5 MV/cm Oe is obtained through calculation provided the interfaces between CFO and P(VDF-co-TrFE) have an appropriate compatible coefficient of about 0.5. The results indicate that the CFO/P(VDF-co-TrFE) double-layer film is a potential multiferroic composite as an attractive candidate for memory storage and spintronic devices.