Corrigendum: Electrospun, Oriented, Ferromagnetic Ni 1-x Fe x Nanofibers.

[This corrects the article DOI: 10.3389/fchem.2020.00047.].

Electrospun, Oriented, Ferromagnetic Ni 1-x Fe x Nanofibers.

Electrospinning has been used to fabricate ferromagnetic Ni0.47Fe0.53 nanofiber mats that were composed of individual, orientated Ni0.47Fe0.53 nanofibers. The key steps were processing a polyvinylpyrrolidone nanofiber template containing ferric nitrate and nickel acetate metal precursors in Ar at 300°C and then 95% Ar: 5% H2 at 600°C. The Ni0.47Fe0.53 fibers were nanostructured and contained Ni0.47Fe0.53 nanocrystals with average diameters of ~14 nm. The Ni0.47Fe0.53 ferromagnetic mats had a high saturation magnetic moment per formula unit that was comparable to those reported in other studies of nanostructured Ni1-x Fe x . There is a small spin-disordered fraction that is typically seen in nanoscale ferromagnets and is likely to be caused by the surface of the nanofibers. There was an additional magnetic contribution that could possibly stem from a small Fe1-z Ni z O phase fraction surrounding the fibers. The coercivity was found to be enhanced when compared with the bulk material.

Unusual 209Bi NMR quadrupole effects in topological insulator Bi2Se3.

Three-dimensional topological insulators are an important class of modern materials, and a strong spin-orbit coupling is involved in making the bulk electronic states very different from those near the surface. Bi2Se3 is a model compound, and 209Bi NMR is employed here to investigate the bulk properties of the material with focus on the quadrupole splitting. It will be shown that this splitting measures the energy band inversion induced by spin-orbit coupling in quantitative agreement with first-principle calculations. Furthermore, this quadrupole interaction is very unusual as it can show essentially no angular dependence, e.g., even at the magic angle the first-order splitting remains. Therefore, it is proposed that the magnetic field direction is involved in setting the quantization axis for the electrons, and that their life time leads to a new electronically driven relaxation mechanism, in particular for quadrupolar nuclei like 209Bi. While a quantitative understanding of these effects cannot be given, the results implicate that NMR can become a powerful tool for the investigation of such systems.

Electrically modulated diffraction gratings in organic chromophore thin films.

An electrically modulated diffraction grating has been demonstrated in poled polymer thin films containing the organic nonlinear optical chromophore, PYR-3 (2-{3-Cyano-4-[3-(1-decyl-1 H-pyridin-4-ylidene)-propenyl]-5,5-dimethy l-5 H-furan-2-ylidene}-malononitrile), and amorphous polycarbonate. A dc electric field induced change in the diffraction efficiency of up to 9% was observed. The diffraction efficiency modulation was likely due to an electric field induced change in the film thickness via a piezoelectric effect rather than via an electronic linear electro-optic effect.

75As NMR study of overdoped CeFeAsO0.8F0.2.

We report on the results from a (75)As nuclear magnetic resonance (NMR) study of the overdoped iron pnictide superconductor CeFeAsO0.8F0.2. We find two As sites with different shifts at temperatures as high as 100 K, which is above the superconducting transition temperature of 39 K, and hence they cannot be attributed to the effect of vortices in the superconducting state as previously suggested (Ghoshray et al 2009 Phys. Rev. B 79 144512). The much larger spin-lattice relaxation rate compared with that found in other pnictides without magnetic rare earth ions, and the temperature dependence of the (75)As NMR shifts for the two central lines, are consistent with the hyperfine coupling from magnetic Ce to As. The low temperature spectra indicate that there are As ions with two different quadrupole splittings. Our findings appear to be consistent with an electronic phase segregation into regions with two different F dopings or the presence of a correlated spatial charge and spin density variations.

Synthesis, alignment, and magnetic properties of monodisperse nickel nanocubes.

This Communication describes the synthesis of highly monodispersed 12 nm nickel nanocubes. The cubic shape was achieved by using trioctylphosphine and hexadecylamine surfactants under a reducing hydrogen atmosphere to favor thermodynamic growth and the stabilization of {100} facets. Varying the metal precursor to trioctylphosphine ratio was found to alter the nanoparticle size and shape from 5 nm spherical nanoparticles to 12 nm nanocubes. High-resolution transmission electron microscopy showed that the nanocubes are protected from further oxidation by a 1 nm NiO shell. Synchrotron-based X-ray diffraction techniques showed the nickel nanocubes order into [100] aligned arrays. Magnetic studies showed the nickel nanocubes have over 4 times enhancement in magnetic saturation compared to spherical superparamagnetic nickel nanoparticles.