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

   https://doi.org/10.3390/jcs5100268  

   Liu, Ying ; Zhou, Peng ; Ge, Bingfeng ; Liu, Jiahui ; Zhang, Jitao ; Zhang, Wei ; Zhang, Tianjing ; Srinivasan, Gopalan ( October 2021 , Journal of Composites Science)

   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 sensorsmore »and high-frequency device applications.« less
2. Strain-mediated magneto-electric interactions in hexagonal ferrite and ferroelectric coaxial nanofibers

   https://doi.org/10.1557/mrc.2020.30  

   Liu, Y. ; Zhou, P. ; Fu, J. ; Iyengar, M. ; Liu, N. ; Du, P. ; Xiong, Y. ; Moiseienko, V. ; Zhang, W. ; Zhang, J. ; et al ( June 2020 , MRS Communications)

   Abstract This report is on the synthesis by electrospinning of multiferroic core-shell nanofibers of strontium hexaferrite and lead zirconate titanate or barium titanate and studies on magneto-electric (ME) coupling. Fibers with well-defined core–shell structures showed the order parameters in agreement with values for nanostructures. The strength of ME coupling measured by the magnetic field-induced polarization showed the fractional change in the remnant polarization as high as 21%. The ME voltage coefficient in H-assembled films showed the strong ME response for the zero magnetic bias field. Follow-up studies and potential avenues for enhancing the strength of ME coupling in the core–shell nanofibers are discussed.
3. In-plane current induced nonlinear magnetoelectric effects in single crystal films of barium hexaferrite

   https://doi.org/10.1038/s41598-022-09363-x  

   Popov, Maksym ; Zavislyak, Igor ; Qu, Hongwei ; Balbashov, A. M. ; Page, M. R. ; Srinivasan, G. ( March 2022 , Scientific Reports)

   This report is on the observation and analysis of nonlinear magnetoelectric effects (NLME) for in-plane currents perpendicularly to the hexagonal axis in single crystals and liquid phase epitaxy grown thin films of barium hexaferrite. Measurements involved tuning of ferromagnetic resonance (FMR) at 56–58 GHz in the multidomain and single domain states in the ferrite by applying a current. Data on the shift in the resonance frequency with input electric power was utilized to estimate the variations in the magnetic parameter that showed a linear dependence on the input electric power. The NLME tensor coefficients were determined form the estimated changes in the magnetization and uniaxial anisotropy field. The estimated NLME coefficients for in-plane currents are shown to be much higher than for currents flowing along the hexagonal axis. Although the frequency shift of FMR was higher for the single domain resonance, the multi-domain configuration is preferable for device applications since it eliminates the need for a large bias magnetic field. Thus, multidomain resonance with current in the basal plane is favorable for use in electrically tunable miniature, ferrite microwave signal processing devices requiring low operating power.
4. Nonlinear magnetoelectric effects in Al-substituted strontium hexaferrite

   https://doi.org/10.1038/s41598-021-88203-w  

   Liu, Ying ; Popov, Maksym ; Zavislyak, Igor ; Qu, Hongwei ; Zhang, T. ; Zhang, Jitao ; Page, M. R. ; Balbashov, A. M. ; Srinivasan, G. ( April 2021 , Scientific Reports)

   This report is on the observation and theory of electric fieldEinduced non-linear magnetoelectric (NLME) effects in single crystal platelets of ferrimagnetic M-type strontium aluminum hexagonal ferrite. Using microwave measurement techniques, it was found that a DC electric field along the hexagonal c-axis results in significant changes in the saturation magnetization and uniaxial magneto-crystalline anisotropy field and these changes are proportional to the square of the applied static electric field. The NLME effects were present with or without an external bias magnetic field. TheE-induced variation in magnetic order parameters is attributed to weakening of magnetic exchange and spin–orbit interactions since conduction electrons in the ferrite are effectively excluded from both interactions while being in transit from one Fe ion to another. We present a phenomenological theory which considers magneto-bielectric effects characterized by a quadratic term in electric fieldEin the free energy density. The coefficients for the NLME coupling terms have been calculated from experimental data and they do show variations with the Al substitution level and the largest rates of change of the saturation magnetization and anisotropy constant change with the applied power were observed for x = 0.4. It was also clear from the study that strength of the NLME effectmore »does not depend on the amount Al substitution, but critically depends on the electrical conductivity of the sample with the highest NLME coefficients estimated for the sample with the highest conductivity. Results of this work are of importance for a new family of electric field tunable, miniature, high frequency ferrite devices.

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5. Y-type hexagonal ferrite-based band-pass filter with dual magnetic and electric field tunability

   https://doi.org/10.1038/s41598-023-28279-8  

   Popov, Maksym ; Xiong, Yuzan ; Zavislyak, Igor ; Chumak, Hryhorii ; Fedorchuk, Oleksandr ; Saha, Sujoy ; Bidthanapally, Rao ; Qu, Hongwei ; Page, Michael R. ; Srinivasan, Gopalan ( January 2023 , Scientific Reports)

   This work is on the design, fabrication and characterization of a hexagonal ferrite band-pass filter that can be tuned either with a magnetic field or an electric field. The filter operation is based on a straight-edge Y-type hexagonal ferrite resonator symmetrically coupled to the input and output microstrip transmission lines. The Zn₂Yfilter demonstrated magnetic field tunability in the 8–12 GHz frequency range by applying an in-plane bias magnetic fieldH₀provided by a built-in permanent magnet. The insertion loss and 3 dB bandwidth within this band were 8.6 ± 0.4 dB and 350 ± 40 MHz, respectively. The electric fieldEtunability of the pass-band of the device was facilitated by the nonlinear magnetoelectric effect (NLME) in the ferrite. TheE-tuning of the center frequency of the filter by (1150 ± 90) MHz was obtained for an input DC electric power of 200 mW. With efforts directed at a significant reduction in the insertion loss, the compact and power efficient magnetic and electric field tunable Zn₂Y band-pass filter has the potential for use in novel reconfigurable RF/microwave devices and communication systems.