More Like this

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 sensors and high-frequency device applications. 

   more » « less
2. 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.

    

   more » « less
3. Redox Ladder of Ni 3 Complexes with Closed‐Shell, Mono‐, and Diradical Triphenylene Units: Molecular Models for Conductive 2D MOFs

   https://doi.org/10.1002/anie.202109304  

   Yang, Luming ; Dincă, Mircea ( September 2021 , Angewandte Chemie International Edition)

   We report the isolation and characterization of a series of trinickel complexes with 2,3,6,7,10,11‐hexaoxytriphenylene (HOTP), [(Me₃TPANi)₃(HOTP)](BF₄)_n(Me₃TPA=N,N,N‐tris[(6‐methyl‐2‐pyridyl)methyl]amine) (n=2, 3, 4 for complexes1,2,3). These complexes comprise a redox ladder whereby the HOTP core displays increasingly quinoidal character as its formal oxidation state changes from −4, to −3, and −2 in1,2, and3, respectively. No formal oxidation state changes occur on Ni, allowing the isolation of singlet diradical, monoradical, and closed‐shell configurations for HOTP in1,2, and3, respectively, with a concomitant decrease in the spin coupling strength upon oxidation. Because the three complexes can be considered models of the smallest building blocks of 2D conductive metal‐organic frameworks such as Ni₉HOTP₄, these results serve as possible inspiration for the construction of extended materials with targeted electric and magnetic properties.

    

   more » « less
4. Redox Ladder of Ni 3 Complexes with Closed‐Shell, Mono‐, and Diradical Triphenylene Units: Molecular Models for Conductive 2D MOFs

   https://doi.org/10.1002/ange.202109304  

   Yang, Luming ; Dincă, Mircea ( September 2021 , Angewandte Chemie)

   We report the isolation and characterization of a series of trinickel complexes with 2,3,6,7,10,11‐hexaoxytriphenylene (HOTP), [(Me₃TPANi)₃(HOTP)](BF₄)_n(Me₃TPA=N,N,N‐tris[(6‐methyl‐2‐pyridyl)methyl]amine) (n=2, 3, 4 for complexes1,2,3). These complexes comprise a redox ladder whereby the HOTP core displays increasingly quinoidal character as its formal oxidation state changes from −4, to −3, and −2 in1,2, and3, respectively. No formal oxidation state changes occur on Ni, allowing the isolation of singlet diradical, monoradical, and closed‐shell configurations for HOTP in1,2, and3, respectively, with a concomitant decrease in the spin coupling strength upon oxidation. Because the three complexes can be considered models of the smallest building blocks of 2D conductive metal‐organic frameworks such as Ni₉HOTP₄, these results serve as possible inspiration for the construction of extended materials with targeted electric and magnetic properties.

    

   more » « less
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.

    

   more » « less