Converse magneto-electric effects in a core-shell multiferroic nanofiber by electric field tuning of ferromagnetic resonance

This report is on studies directed at the nature of magneto-electric (ME) coupling by ferromagnetic resonance (FMR) under an electric field in a coaxial nanofiber of nickel ferrite (NFO) and lead zirconate titanate (PZT). Fibers with ferrite cores and PZT shells were prepared by electrospinning. The core-shell structure of annealed fibers was confirmed by electron- and scanning probe microscopy. For studies on converse ME effects, i.e., the magnetic response of the fibers to an applied electric field, FMR measurements were done on a single fiber with a near-field scanning microwave microscope (NSMM) at 5-10 GHz by obtaining profiles of both amplitude and phase of the complex scattering parameter S₁₁ as a function of bias magnetic field. The strength of the voltage-ME coupling A_v was determined from the shift in the resonance field H_r for bias voltage of V = 0-7 V applied to the fiber. The coefficient A_v for the NFO core/PZT shell structure was estimated to be - 1.92 kA/Vm (- 24 Oe/V). A model was developed for the converse ME effects in the fibers and the theoretical estimates are in good agreement with the data.