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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 bothmore »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-induced resonances in the dynamical quadratic magnetoelectric response of multiferroics

   https://doi.org/10.1038/s41524-020-0311-z  

   Sayedaghaee, S. Omid ; Paillard, Charles ; Prosandeev, Sergey ; Xu, Bin ; Bellaiche, Laurent ( May 2020 , npj Computational Materials)

   For the last few years, the research interest in magnetoelectric (ME) effect, which is the cross-coupling between ferroelectric and magnetic ordering in multiferroic materials, has experienced a significant revival. The extensive recent studies are not only conducted towards the design of sensors, actuators, transducers, and memory devices by taking advantage of the cross-control of polarization (or magnetization) by magnetic (or electric) fields, but also aim to create a clearer picture in understanding the sources of ME responses and the novel effects associated with them. Here we derive analytical models allowing to understand the striking and novel dynamics of MEmore »effects in multiferroics and further confirm it with atomistic simulations. Specifically, the role of strain is revealed to lead to the existence of electroacoustic magnons, a new quasiparticle that mixes acoustic and optical phonons with magnons, which results in resonances and thus a dramatic enhancement of magnetoelectric responses. Moreover, a unique aspect of the dynamical quadratic ME response under a magnetic field with varying frequencies, which is the second harmonic generation (SHG), has not been discussed prior to the present work. These SHGs put emphasis on the fact that nonlinearities should be considered while dealing with such systems.

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3. Hybrid conjugated polymer/magnetic nanoparticle composite nanofibers through cooperative non-covalent interactions

   https://doi.org/10.1039/D0NA00191K  

   Meng, Lingyao ; Watson, Brad W. ; Qin, Yang ( June 2020 , Nanoscale Advances)

   Hybrid organic–inorganic composites possessing both electronic and magnetic properties are promising materials for a wide range of applications. Controlled and ordered arrangement of the organic and inorganic components is key for synergistic cooperation toward desired functions. In this work, we report the self-assemblies of core–shell composite nanofibers from conjugated block copolymers and magnetic nanoparticles through the cooperation of orthogonal non-covalent interactions. We show that well-defined core–shell conjugated polymer nanofibers can be obtained through solvent induced self-assembly and polymer crystallization, while hydroxy and pyridine functional groups located at the shell of nanofibers can immobilize magnetic nanoparticles via hydrogen bonding and coordinationmore »interactions. These precisely arranged nanostructures possess electronic properties intrinsic to the polymers and are simultaneously responsive to external magnetic fields. We applied these composite nanofibers in organic solar cells and found that these non-covalent interactions led to controlled thin film morphologies containing uniformly dispersed nanoparticles, although high loadings of these inorganic components negatively impact device performance. Our methodology is general and can be utilized to control the spatial distribution of functionalized organic/inorganic building blocks, and the magnetic responsiveness and optoelectronic activities of these nanostructures may lead to new opportunities in energy and electronic applications.« less
4. Designing iridate-based superlattice with large magnetoelectric coupling

   https://doi.org/10.1039/C9TC04466C  

   Dasa, Tamene R. ; Hao, Lin ; Liu, Jian ; Xu, Haixuan ( October 2019 , Journal of Materials Chemistry C)

   The coupling between ferroelectric and magnetic order provides a powerful means to control magnetic properties with electric fields. In this study, we have investigated the magnetoelectric (ME) coupling in iridate-oxide based superlattices employing first-principles density functional theory (DFT) calculations. In particular, we have investigated several oxide superlattices, including (SrIrO 3 ) 1 –(CaTiO 3 ) 1 (SIO–CTO) and (SrIrO 3 ) 1 –(BaTiO 3 ) 1 (SIO–BTO), with an alternating single layer of SIO and CTO/BTO. We identify a very large ME coupling in SIO–BTO mediated by both lattice and electronic contributions. In comparison, moderate ME coupling constants are foundmore »in SIO–CTO. Further electronic and structural analyses reveal that the large ME coupling of SIO–BTO is caused by the large spin–orbit coupling of 5d iridium as well as the significant polarization induced in the SIO–BTO. Interestingly, we find that the ME coupling in SIO–BTO can further be enhanced by modulating epitaxial strain. These results suggest a route to significantly enhance the ME coupling effects, which might be applicable for other materials and practical applications.« less
5. Superparamagnetic Fe/Au Nanoparticles and Their Feasibility for Magnetic Hyperthermia

   https://doi.org/10.3390/app11146637  

   Sanad, Mohamed F. ; Meneses-Brassea, Bianca P. ; Blazer, Dawn S. ; Pourmiri, Shirin ; Hadjipanayis, George C. ; El-Gendy, Ahmed A. ( July 2021 , Applied Sciences)

   Today, magnetic hyperthermia constitutes a complementary way to cancer treatment. This article reports a promising aspect of magnetic hyperthermia addressing superparamagnetic and highly Fe/Au core-shell nanoparticles. Those nanoparticles were prepared using a wet chemical approach at room temperature. We found that the as-synthesized core shells assembled with spherical morphology, including face-centered-cubic Fe cores coated and Au shells. The high-resolution transmission microscope images (HRTEM) revealed the formation of Fe/Au core/shell nanoparticles. The magnetic properties of the samples showed hysteresis loops with coercivity (HC) close to zero, revealing superparamagnetic-like behavior at room temperature. The saturation magnetization (MS) has the value of 165more »emu/g for the as-synthesized sample with a Fe:Au ratio of 2:1. We also studied the feasibility of those core-shell particles for magnetic hyperthermia using different frequencies and different applied alternating magnetic fields. The Fe/Au core-shell nanoparticles achieved a specific absorption rate of 50 W/g under applied alternating magnetic field with amplitude 400 Oe and 304 kHz frequency. Based on our findings, the samples can be used as a promising candidate for magnetic hyperthermia for cancer therapy.« less