Magnetic properties of iron-doped channels in H-Nb₂O₅

Abstract

H-Nb2 O5 (Nb28 O70 ) is a semiconductor whose structure is built of NbO6 octahedra, which share corners and edges to form blocks parallel to the basal ac plane of the structure. One unit cell contains two blocks of 3 × 4 and 3 × 5 octahedra displaced by 1/2 b -axis spacing, besides one further Nb atom located in tetrahedrally coordinated sites along channels parallel to the b axis. Such channels contain octahedral interstices which are the preferential sites for point defect segregation in this structure. The possibility of using the channels as a framework for obtaining oriented spin arrays has never been explored in the literature. To investigate which kind of magnetic interaction would arise we manufactured a sample of H-Nb2 O5 containing enough Fe to fill part of the octahedral interstices in the channels and measured the ac susceptibility response. The results were consistent with the formation of linear chains of spins, with variable coupling constants along the chains. The variable coupling can be understood as a consequence of the influence of the large number of possible arrangements of Nb and Fe atoms along the channels upon the sign and magnitude of superexchange interactions mediated by the oxygen atoms.

Magnetic impurities in HNb2O5

“…The magnetic properties measured in doped H-phase are related to magnetic moments localized on the dopants rather than the matrix, which is mostly non-magnetic since it is formed by d 0 Nb 5+ ions (and also by spin-paired d 1 Nb 4+ ions when reduced to Nb 2 O 5−x ). The present paper complements our previous study on the subject, hereafter referred to as part I [4]. In part I we carried out dc and ac magnetic susceptibility measurements in an Fe-doped sample of H-phase (here called sample Fe-I), which were consistent with the formation of one-dimensional arrays of Fe 2+ along the b-axis channels in the structure.…”

Electron diffraction by plasmon waves

“…Plasmons sustained by nanostructured conductors (a prototypical class of evanescent fields), can extend toward the surrounding vacuum and enable large interaction with free electrons. As a result of this interaction, electrons can absorb previously generated plasmons [13] and also excite plasmons that are subsequently outcoupled to cathodoluminescence light emission. The latter is widely used to spectrally and spatially map plasmons and other nanoscale optical modes [14,15].…”

Mixtures of anisotropic and spherical colloids: Phase behavior, confinement, percolation phenomena and kinetics

“…are concerned, one expects that simple hard spheres should be a very good model. However, the variation of the observed nucleation rates with the supersaturation of the colloidal suspension differs strongly from the corresponding simulation results [46][47][48][49][50][51]. The physical reason for this discrepancy hitherto has not been understood.…”

“…Thus nucleation rates measured in suspensions with different solvents cannot be straightforwardly compared, crystallization kinetics is affected by solvent hydrodynamics substantially. This shows already that the previous comparison of simulations [49][50][51] where hydrodynamics was ignored, with experiments (where it is inevitably present) presumably are not so meaningful. We note that also in phase separation kinetics of colloid-polymer mixtures the importance of hydrodynamic interactions could be demonstrated by simulations using the MPC method [20].…”

“…4b demonstrates that the actual value of the plateau must depend on the arbitrary parameter A/L used to define connectivity, but the qualitative behavior is the same for all A/L ≤ 1. One can understand this behavior qualitatively from a cell model argument, which states that each disk occupies an effective A particularly interesting problem which has found attention both from experiment [46][47][48] and from simulations [49][50][51] is the nucleation of crystals of hard-sphere like colloids from the fluid phase. As far as static properties (e.g.…”