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1. 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.

    

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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. 

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3. The Growth of Polarization Domains in Ultrathin Ferroelectric Films Seeded by the Tip of an Atomic Force Microscope

   https://doi.org/10.1186/s11671-022-03688-2  

   Zamani-Alavijeh, Mohammad ; Morgan, Timothy A. ; Kuchuk, Andrian V. ; Salamo, Gregory J. ( May 2022 , Nanoscale Research Letters)

   Piezoresponse force microscopy is used to study the velocity of the polarization domain wall in ultrathin ferroelectric barium titanate (BTO) films grown on strontium titanate (STO) substrates by molecular beam epitaxy. The electric field due to the cone of the atomic force microscope tip is demonstrated as the dominant electric field for domain expansion in thin films at lateral distances greater than about one tip diameter away from the tip. The velocity of the domain wall under the applied electric field by the tip in BTO for thin films (less than 40 nm) followed an expanding process given by Merz’s law. The material constants in a fit of the data to Merz’s law for very thin films are reported as about 4.2 KV/cm for the activation field,$$E_{\mathrm{a}}$$$E_a$, and 0.05 nm/s for the limiting velocity,$$v_{\infty }$$$v_{\infty }$. These material constants showed a dependence on the level of strain in the films, but no fundamental dependence on thickness.

    

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4. 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.

    

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5. Nonvolatile Electric‐Field Control of Ferromagnetic Resonance and Spin Pumping in Pt/YIG at Room Temperature

   https://doi.org/10.1002/aelm.201800663  

   Yu, Rui ; He, Kang ; Liu, Qi ; Gan, Xucheng ; Miao, Bingfeng ; Sun, Liang ; Du, Jun ; Cai, Hongling ; Wu, Xiaoshan ; Wu, Mingzhong ; et al ( February 2019 , Advanced Electronic Materials)

   Electric‐field‐controlled magnetism is of importance in realizing energy efficient, dense and fast information storage and processing. Strain‐mediated converse magneto‐electric (ME) coupling between ferromagnetic and ferroelectric heterostructure shows promise for realizing electric‐controlled magnetism at room temperature and is attracting a number of recent investigations. However, such ME‐effect studies have mainly focus on magnetic metals. In this work, high quality yttrium iron garnet (Y₃Fe₅O₁₂(YIG)) films are deposited directly onto (100)‐oriented single‐crystal Pb (Mg_1/3Nb_2/3)_0.7Ti_0.3O₃(PMN‐PT) substrates by means of magnetron sputtering. The electric‐field‐induced polarization switching and lattice strain in the PMN‐PT substrate results in two distinct magnetization states in the YIG film that are nonvolatile and electrically reversible. Because of the direct contact between the YIG and the PMN‐PT substrate, an efficient ME coupling and an almost 90° rotation of the easy axis of the YIG film can be realized. Furthermore, the electric‐field‐controlled hysteresis loop‐like ferromagnetic resonance field shifts and spin pumping signals are observed in Pt/YIG/PMN‐PT heterostructures. Thus, the obstacle is overcome via growing high‐quality YIG thin films directly onto PMN‐PT substrates and an efficient manipulation of magnetism and pure spin current transport by electric field is thereby realized. These findings are instructive for future low‐power magnetic insulator‐based spintronic devices.

    

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