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.
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Colossal Magnetoelectric Effect in Core–Shell Magnetoelectric Nanoparticles
Magnetoelectric coefficient values of above 5 and 2 V cm–1 Oe–1 in 20 nm CoFe2O4–BaTiO3 and NiFe2O4–BaTiO3 core–shell magnetoelectric nanoparticles were demonstrated. These colossal values, compared to 0.1 V cm–1 Oe–1 commonly reported for the 0–3 system, are attributed to (i) the heterostructural lattice-matched interface between the magnetostrictive core and the piezoelectric shell, confirmed through transmission electron microscopy, and (ii) in situ scanning tunneling microscopy nanoprobe-based ME characterization. The nanoprobe technique allows measurements of the ME effect at a single-nanoparticle level which avoids the charge leakage problem of traditional powder form measurements. The difference in the frequency dependence of the ME value between the two material systems is owed to the Ni-ferrite cores becoming superparamagnetic in the near-dc frequency range. The availability of novel nanostructures with colossal ME values promises to unlock many new applications ranging from energy-efficient information processing to nanomedicine and brain–machine interfaces.
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- Award ID(s):
- 1935841
- NSF-PAR ID:
- 10181001
- Date Published:
- Journal Name:
- Nano Letters
- ISSN:
- 1530-6984
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.nanolett.0c01588
