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

Abstract

Magnetoelectric (ME) composite materials, in which the coupling between magnetostricitve and piezoelectric effects is achieved, are potential candidates for multifunctional devices where the interplay between electrical, magnetic and mechanical properties of these structures can be fully exploited. Nanostructured composites are particularly interesting due to the enhancement of ME coupling expected at the nanoscale. However, direct studies of ME coupling in nanocomposites by scanning probe techniques are rare due to the complex interplay of forces at play, including those arising from electrostatic, magnetic and electromechanical interactions. In this work, the ME coupling of coaxial nickel-polyvinylidene fluoride trifluoroethylene [Ni-P(VDF-TrFE)] composite nanowires, fabricated by a scalable template-wetting based technique, is studied using a systematic sequence of scanning probe techniques. Individual ME nanowires were subjected to an electric field sufficient for ferroelectric poling in piezoresponse force microscopy (PFM) mode, while magnetic force microscopy (MFM) was used 2 to measure localised changes in magnetization as a result of electrical poling. Kelvin probe force microscopy (KPFM) measurements of surface potential were conducted to eliminate for the effect of contact potential differences during these measurements. An inverse, static, magnetoelectric coupling coefficient of ~1 x 10-11 s m-1 was found in our coaxial nanocomposite nanowires, comparable to other types of planar composites studied in this work, despite having an inferior piezoelectric-to-magnetostrictive volume ratio. The efficient ME coupling in our coaxial nanowires is attributed to the larger surface-to-volume interfacial contact between Ni and P(VDF-TrFE), and is promising for future integration into ME composite devices such as magnetic field sensors or energy harvesters.

Magnetoelectric coupling in CoFe2O4‐Pb(Zr0.2Ti0.8)O3 coaxial nanofibers

“…Frequency shift Δf between peaks and troughs were used as an indication for the magnetization changes in the NFs, as developed by Boughey and Bai. 3,11 It is observed that Δf increases with the increase in poling voltage, indicating the high response of the ME coupling under high poling voltages. As shown in Figure 5C, the frequency shift (Δf 1 ) is about 0.6 kHz for non-poling NF (0 V), whereas after the NF was poled under 6 V, the frequency shift (Δf 2 ) was increased to 1.1 kHz, indicating the magnetization changed after an electric field poling in PFM mode.…”

“…As shown in Figure 5C, the frequency shift (Δf 1 ) is about 0.6 kHz for non-poling NF (0 V), whereas after the NF was poled under 6 V, the frequency shift (Δf 2 ) was increased to 1.1 kHz, indicating the magnetization changed after an electric field poling in PFM mode. According to the method used by Boughey 3 and Bai, 11 the magnetization (M i ) was considered to have a linear relation to the measured frequency shift (Δf i ) before and after electrical poling. This can be expressed by the following equation:…”

“…Figure 5C depicts the line profiles of the coaxial NF before and after applying the electric voltage of 6 V which is used to obtain the frequency signal from the MFM images. Frequency shift Δ f between peaks and troughs were used as an indication for the magnetization changes in the NFs, as developed by Boughey and Bai 3,11 . It is observed that Δ f increases with the increase in poling voltage, indicating the high response of the ME coupling under high poling voltages.…”

“…1 The effective ME coupling emerges multi-functionality to design low-power, ultra-fast, and multi-functional electronic devices. Compared with bulk and thin film, nanocomposites exhibit improved elastic, piezoelectric, and ME properties, 2,3 due to their large specific surface area and the increased interfacial surface area in connection with two phases. This special interfacial structure increases the stress transfer efficiency and thus the ME coupling response.…”

“…Most of the previous reports focused on the magnetic field control of the polarization in ME NFs by detecting the piezoelectric response change under an external magnetic field, indicating magnetic-field induced ferroelectric polarization switching. 2,[8][9][10] While seldom works has focused on the magnetic-field induced electric order change, 3,11 especially in nanoscale though the converse ME effect also provide the opportunity to realize novel devices in electric field-tunable radiofrequency/microwave signal processing, magnetic field sensor, and ultralow power logic-memory, etc. [12][13][14] Therefore, it is of significance to qualitatively and quantitatively estimate the converse ME coefficients at nanometer length scale.…”