ABSTRACT
Thin flakes of Cr1/3NbS2 are fabricated successfully via microexfoliation techniques. Temperature-dependent and field-dependent magnetizations of thin flakes with various thicknesses are investigated. When the thickness of the flake is around several hundred nanometers, the softening and eventual disappearance of the bulk soliton peak is accompanied by the appearance of other magnetic peaks at lower magnetic fields. The emergence and annihilation of the soliton peaks are explained and simulated theoretically by the change in spin spiral number inside the soliton lattice due to dimensional confinement. Compared to the conventional magnetic states in nanoscale materials, the stability and thickness tunability of quantified spin spirals make Cr1/3NbS2 a potential candidate for spintronics nanodevices beyond Moore's law.
ABSTRACT
We report the synthesis of single-crystal iron germanium nanowires via chemical vapor deposition without the assistance of any catalysts. The assembly of single-crystal FeGe2 nanowires with tetragonal C16 crystal structure shows anisotropic magnetic behavior along the radial direction or the growth axial direction, with both antiferromagnetic and ferromagnetic orders. Single FeGe2 nanowire devices were fabricated using e-beam lithography. Electronic transport measurement in these devices show two resistivity anomalies near 250 K and 200 K which are likely signatures of the two spin density wave states in FeGe2.
ABSTRACT
A metastable phase α-FeSi_{2} was epitaxially stabilized on a silicon substrate using pulsed laser deposition. Nonmetallic and ferromagnetic behaviors are tailored on α-FeSi_{2} (111) thin films, while the bulk material of α-FeSi_{2} is metallic and nonmagnetic. The transport property of the films renders two different conducting states with a strong crossover at 50 K, which is accompanied by the onset of a ferromagnetic transition as well as a substantial magnetoresistance. These experimental results are discussed in terms of the unusual electronic structure of α-FeSi_{2} obtained within density functional calculations and Boltzmann transport calculations with and without strain. Our finding sheds light on achieving ferromagnetic semiconductors through both their structure and doping tailoring, and provides an example of a tailored material with rich functionalities for both basic research and practical applications.
ABSTRACT
Particularly in Sr2IrO4, the interplay between spin-orbit coupling, bandwidth and on-site Coulomb repulsion stabilizes a J(eff) = 1/2 spin-orbital entangled insulating state at low temperatures. Whether this insulating phase is Mott- or Slater-type, has been under intense debate. We address this issue via spatially resolved imaging and spectroscopic studies of the Sr2IrO4 surface using scanning tunneling microscopy/spectroscopy (STM/S). STS results clearly illustrate the opening of an insulating gap (150 ~ 250 meV) below the Néel temperature (TN), in qualitative agreement with our density-functional theory (DFT) calculations. More importantly, the temperature dependence of the gap is qualitatively consistent with our DFT + dynamical mean field theory (DMFT) results, both showing a continuous transition from a gapped insulating ground state to a non-gap phase as temperatures approach TN. These results indicate a significant Slater character of gap formation, thus suggesting that Sr2IrO4 is a uniquely correlated system, where Slater and Mott-Hubbard-type behaviors coexist.
ABSTRACT
The crystal and magnetic structures of single-crystalline hexagonal LuFeO(3) films have been studied using x-ray, electron, and neutron diffraction methods. The polar structure of these films are found to persist up to 1050 K; and the switchability of the polar behavior is observed at room temperature, indicating ferroelectricity. An antiferromagnetic order was shown to occur below 440 K, followed by a spin reorientation resulting in a weak ferromagnetic order below 130 K. This observation of coexisting multiple ferroic orders demonstrates that hexagonal LuFeO(3) films are room-temperature multiferroics.
ABSTRACT
Self-assembled monolayers are the basis for molecular nanodevices, flexible surface functionalization, and dip-pen nanolithography. Yet self-assembled monolayers are typically created by a rather inefficient process involving thermally driven attachment reactions of precursor molecules to a metal surface, followed by a slow and defect-prone molecular reorganization. Here we demonstrate a nonthermal, electron-induced approach to the self-assembly of phenylacetylene molecules on gold that allows for a previously unachievable attachment of the molecules to the surface through the alkyne group. While thermal excitation can only desorb the parent molecule due to prohibitively high activation barriers for attachment reactions, localized injection of hot electrons or holes not only overcomes this barrier but also enables an unprecedented control over the size and shape of the self-assembly, defect structures, and the reverse process of molecular disassembly from a single molecule to a mesoscopic length scale. Electron-induced excitation may therefore enable new and highly controlled approaches to molecular self-assembly on a surface.
