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The preparation of magnetic nanotubes opens new avenues in nanobiotechnology as a consequence of their multiple properties embedded within the same moiety. Here, we report on synthesis and characterization of titanate nanotubes and their Fe-/Co-doped by means of X-ray diffraction, high-resolution transmission electron microscopy, and magnetic studies. Although the absence of 3d elements in Na2Ti3O7 nanotubes, our data for the first time, exhibits room temperature M−H hysteresis. Furthermore, our results show that the magnetization increased with Fe doping, while Co doping enhanced the coercivity. This behaviour was expected from the magnetic character of Fe and the positive magnetocrystalline anisotropy of Co. These results give access to the doping effect on tuning the properties of Na2Ti3O7 nanotubes.

Static and dynamic magnetic properties of P$\overline{3}$1$m$-phase ${\mathrm{MnSb}}_{2}{\mathrm{O}}_{6}$ have been studied by means of muon-spin relaxation ($\ensuremath{\mu}\mathrm{SR}$), high-frequency electron-spin resonance (HF-ESR), specific heat, and magnetization studies in magnetic fields up to 25 T. The data imply onset of long-range antiferromagnetic order at ${T}_{\mathrm{N}}$ = 8 K and a spin-flop-like transition at ${B}_{\mathrm{SF}}$ $\ensuremath{\approx}$ 0.7--1 T. Below ${T}_{\mathrm{N}}$, muon asymmetry exhibits well-defined oscillations indicating a narrow distribution of the local fields. A competing antiferromagnetic phase appearing below ${T}_{\mathrm{N}2}$ = 5.3 K is evidenced by a step in the magnetization and a slight kink of the relaxation rate. Above ${T}_{\mathrm{N}}$, both $\ensuremath{\mu}\mathrm{SR}$ and HF-ESR data suggest short-range spin order. HF-ESR data show that local magnetic fields persist up to at least $12{T}_{\mathrm{N}}\ensuremath{\approx}100$ K. Analysis of the antiferromagnetic resonance modes and the thermodynamic spin-flop field suggest zero-field splitting of $\mathrm{\ensuremath{\Delta}}\ensuremath{\approx}18$ GHz which implies small but finite magnetic anisotropy.

We review the features of the charge density wave (CDW) conductor $\mathrm{Nb}{\mathrm{S}}_{3}$ (phase II) and include several additional results from transport, compositional, and structural studies. Particularly, we highlight three central results: (1) In addition to the previously reported CDW transitions at ${T}_{\mathrm{P}1}=360\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${T}_{\mathrm{P}2}=150\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, a third CDW transition occurs at a much higher temperature ${T}_{\mathrm{P}0}\ensuremath{\approx}620\ensuremath{-}650\phantom{\rule{0.16em}{0ex}}\mathrm{K}$; evidence for the nonlinear conductivity of this CDW is presented. (2) We show that the CDW associated with the ${T}_{\mathrm{P}2}$ transition arises from S vacancies acting as donors. Such a CDW transition has not been observed before. (3) We demonstrate the exceptional coherence of the ${T}_{\mathrm{P}1}$ CDW at room temperature. The effects of uniaxial strain on the CDW transition temperature and transport are reported.

Elucidating the microscopic origin of nematic order in iron-based superconducting materials is important because the interactions that drive nematic order may also mediate the Cooper pairing. Nematic order breaks fourfold rotational symmetry in the iron plane, which is believed to be driven by either orbital or spin degrees of freedom. However, as the nematic phase often develops at a temperature just above or coincides with a stripe magnetic phase transition, experimentally determining the dominant driving force of nematic order is difficult. Here, we use neutron scattering to study structurally the simplest iron-based superconductor FeSe, which displays a nematic (orthorhombic) phase transition at $T_s=90$ K, but does not order antiferromagnetically. Our data reveal substantial stripe spin fluctuations, which are coupled with orthorhombicity and are enhanced abruptly on cooling to below $T_s$. Moreover, a sharp spin resonance develops in the superconducting state, whose energy (~4 meV) is consistent with an electron boson coupling mode revealed by scanning tunneling spectroscopy, thereby suggesting a spin fluctuation-mediated sign-changing pairing symmetry. By normalizing the dynamic susceptibility into absolute units, we show that the magnetic spectral weight in FeSe is comparable to that of the iron arsenides. Our findings support recent theoretical proposals that both nematicity and superconductivity are driven by spin fluctuations., Comment: 19 pages, 8 figures