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1. 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.
2. 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
3. Effect of manganese substitution of ferrite nanoparticles on particle grain structure

   https://doi.org/10.1039/D2NA00200K  

   Yan, Zichun ; Chaluvadi, Anish ; FitzGerald, Sara ; Spence, Sarah ; Bleyer, Christopher ; Zhu, Jiazhou ; Crawford, Thomas M. ; Getman, Rachel B. ; Watt, John ; Huber, Dale L. ; et al ( August 2022 , Nanoscale Advances)

   To investigate the influence of manganese substitution on the saturation magnetization of manganese ferrite nanoparticles, samples with various compositions (MnxFe3−xO4,x = 0, 0.25, 0.5, 0.75, and 1) were synthesized and characterized. The saturation magnetization of such materials was both calculated using density functional theory and measured via vibrating sample magnetometry. A discrepancy was found; the computational data demonstrated a positive correlation between manganese content and saturation magnetization, while the experimental data exhibited an inverse correlation. X-ray diffraction (XRD) and magnetometry results indicated that the crystallite diameter and the magnetic diameter decrease when adding more manganese, which could explain the loss of magnetization of the particles. For 20 nm nanoparticles, with increasing manganese substitution level, the crystallite size decreases from 10.9 nm to 6.3 nm and the magnetic diameter decreases from 15.1 nm to 3.5 nm. Further high resolution transmission electron microscopy (HRTEM) analysis confirmed the manganese substitution induced defects in the crystal lattice, which encourages us to find ways of eliminating crystalline defects to make more reliable ferrite nanoparticles.
4. Converse magneto-electric effects in a core–shell multiferroic nanofiber by electric field tuning of ferromagnetic resonance

   https://doi.org/10.1038/s41598-020-77041-x  

   Liu, Ying ; Sreenivasulu, G. ; Zhou, P. ; Fu, J. ; Filippov, D. ; Zhang, W. ; Zhou, T. ; Zhang, T. ; Shah, Piyush ; Page, M. R. ; et al ( November 2020 , Scientific Reports)

   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 parameterS₁₁as a function of bias magnetic field. The strength of the voltage-ME couplingA_vwas determined from the shift in the resonance fieldH_rfor bias voltage ofV = 0–7 V applied to the fiber. The coefficientA_vfor 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.
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.