Coaxial Nickel–Poly(vinylidene fluoride trifluoroethylene)\nNanowires for Magnetoelectric Applications

Abstract

Magnetoelectric\n(ME) composite materials, in which a coupling between\nmagnetostrictive and piezoelectric effects is achieved, are potential\ncandidates for multifunctional devices where the interplay between\nthe electrical, magnetic, and mechanical properties of these structures\ncan be fully exploited. Nanostructured composites are particularly\ninteresting because of the enhancement of ME coupling expected at\nthe nanoscale. However, direct studies of ME coupling in nanocomposites\nby scanning probe microscopy (SPM) techniques are rare because of\nthe complex interplay of forces at play, including those arising from\nelectrostatic, magnetic, and electromechanical interactions. In this\nwork, the ME coupling of coaxial nickel–poly­(vinylidene fluoride\ntrifluoroethylene) [Ni–P­(VDF-TrFE)] composite nanowires (NWs),\nfabricated by a scalable template-wetting-based technique, is studied\nusing a systematic sequence of SPM techniques. Individual ME NWs were\nsubjected to an electric field sufficient for ferroelectric poling\nin piezoresponse force microscopy (PFM) mode, while magnetic force\nmicroscopy (MFM) was used to measure localized changes in magnetization\nas a result of electrical poling. Kelvin probe force microscopy measurements\nof the surface potential were conducted to eliminate for the effect\nof contact potential differences during these measurements. An inverse,\nstatic, ME coupling coefficient of ∼1 × 10^–11 s m^–1 was found in our coaxial nanocomposite NWs,\ncomparable to other types of planar composites studied in this work,\ndespite having an inferior piezoelectric-to-magnetostrictive volume\nratio. The efficient ME coupling in our coaxial NWs is attributed\nto the larger surface-to-volume interfacial contact between Ni and\nP­(VDF-TrFE) and is promising for future integration into ME composite\ndevices such as magnetic field sensors or energy harvesters.