Strain-Mediated Magneto-Electric Effects in Coaxial Nanofibers of Y/W-Type Hexagonal Ferrites and Ferroelectrics

Ying Liu,Wei Zhang,Peng Zhou,Jiahui Liu,Tianjing Zhang,Gopalan Srinivasan,Jitao Zhang,Bingfeng Ge

doi:10.3390/jcs5100268

Abstract

Nanofibers of Y- or W-type hexagonal ferrites and core–shell fibers of hexagonal ferrites and ferroelectric lead zirconate titanate (PZT) or barium titanate (BTO) were synthesized by electrospinning. The fibers were found to be free of impurity phases, and the core–shell structure was confirmed by electron and scanning probe microscopy. The values of magnetization of pure hexagonal ferrite fibers compared well with bulk ferrite values. The coaxial fibers showed good ferroelectric polarization, with a maximum value of 0.85 μC/cm2 and 2.44 μC/cm2 for fibers with BTO core–Co2W shell and PZT core–Ni2Y shell structures, respectively. The magnetization, however, was much smaller than that for bulk hexaferrites. Magneto-electric (ME) coupling strength was characterized by measuring the ME voltage coefficient (MEVC) for magnetic field-assembled films of coaxial fibers. Among the fibers with Y-type, films with Zn2Y showed a higher MEVC than films with Ni2Y, and fibers with Co2W had a higher MEVC than that of those with Zn2W. The highest MEVC of 20.3 mV/cm Oe was measured for Co2W–PZT fibers. A very large ME response was measured in all of the films, even in the absence of an external magnetic bias field. The fibers studied here have the potential for use in magnetic sensors and high-frequency device applications.

Highlights

The magneto-electric (ME) effects in ferromagnetic–ferroelectric composites have been a topic of fundamental and technological interests in recent years [1,2,3,4,5]
Two types of ME effects are studied in such composites. These are the direct ME effect (DME), i.e., the response of the composite to an applied magnetic field that is measured as variations in the ferroelectric order parameters, and the converse ME effect (CME), which is the response of the composite to an applied electric field and measured in terms of changes in magnetic parameters [5]
We have previously reported on ME effects in coaxial fibers of ferrites and ferroelectric lead zirconate titanate (PZT) and barium titanate (BTO) [15,16]

Summary

Introduction

The magneto-electric (ME) effects in ferromagnetic–ferroelectric composites have been a topic of fundamental and technological interests in recent years [1,2,3,4,5]. Two types of ME effects are studied in such composites. These are the direct ME effect (DME), i.e., the response of the composite to an applied magnetic field that is measured as variations in the ferroelectric order parameters, and the converse ME effect (CME), which is the response of the composite to an applied electric field and measured in terms of changes in magnetic parameters [5]. Measurement techniques for the strength of DME effects include the ME voltage coefficient and variations in the ferroelectric polarization and dielectric constant under an applied magnetic field H. For CME effects, one may measure the changes in the magnetization or the magnetic anisotropy field under an applied electric field E. Use of the composites as magnetic sensors, multiple-states memory devices, low-power spintronics, energy harvesting, and microwave devices has recently been investigated [6,7,8,9]

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Conclusion