Modification of magnetoelectric properties of thin film composite multiferroics of Fe10Ni90/PVDF type with using nanostructured Fe10Ni90 layer

Abstract

In this work, we study the effectiveness of using nanostructuring of a magnetostrictive Fe10Ni90 layer in a film composite multiferroic of the [Fe10Ni90/Cu]p/Fe10Ni90/PVDF type in order to obtain the maximum magnetoelectric effect (ME) while maintaining the high magnetosensitivity characteristic of thin Fe10Ni90 films. In this case, such nanostructuring parameters as the number of periods p and the thickness LFeNi of the Fe–Ni sublayers were varied. The analysis of the dependences of the ME coefficient αE on the indicated parameters carried out in this work made it possible to identify the optimal configuration of the multiferroic. Thus, the work shows that in the non-resonant mode the highest ME coupling coefficient (αE = 4.2 V/cm∙Oe) is achieved for a structure with p = 4 and LFeNi = 200 nm in a saturation field of ∼50 Oe, and a close to linear change in αE is realized in the field range 6–15 Oe. At the same time, this structure retains a low coercive field Hc ∼ 4–5 Oe and pronounced uniaxial magnetic anisotropy in the film plane. These facts indicate the absence in the magnetic component of the multiferroic structure of an undesirable “supercritical” magnetic state, which appears in unstructured Fe10Ni90 films with equivalent thicknesses of the ferromagnetic layer and sharply worsens its magnetosensitivity. Thus, in the case of a homogeneous magnetic layer, the thickness of which is equivalent to the total thickness of the magnetic phase of a nanostructured multiferroic (1000 nm), a significantly lower value of αE = 1.6 V/cm∙Oe is achieved. The totality of the data obtained indicates the validity of using the nanostructuring method when optimizing the properties of film composite multiferroics. A detailed analysis of the dependences αE(p) and αE (LFeNi) together with the results of computer modeling made it possible to determine the main factors influencing the value of αE. In particular, it is shown that an increase in αE is primarily caused by an increase in the total volume of the magnetostrictive phase in the composite, as well as a weakening of the damping effect of the substrate, which occurs with an increase in the number of periods and the thickness of individual sublayers in the structure.