5 research outputs found
Reversible Tuning of Collinear versus Chiral Magnetic Order by Chemical Stimulus
The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction mediates collinear
magnetic interactions via the conduction electrons of a non-magnetic spacer,
resulting in a ferro- or antiferromagnetic magnetization in magnetic
multilayers. The resulting spin-polarized charge transport effects have found
numerous applications. Recently it has been discovered that heavy non-magnetic
spacers are able to mediate an indirect magnetic coupling that is non-collinear
and chiral. This Dzyaloshinskii-Moriya-enhanced RKKY (DME-RKKY) interaction
causes the emergence of a variety of interesting magnetic structures, such as
skyrmions and spin spirals. Applications using these magnetic quasi-particles
require a thorough understanding and fine-tuning of the balance between the
Dzyaloshinskii-Moriya interaction and other magnetic interactions, e.g., the
exchange interaction and magnetic anisotropy contributions. Here, we show by
spin-polarized scanning tunneling microscopy that the spin structure of
manganese oxide chains on Ir(001) can reproducibly be switched from chiral to
collinear antiferromagnetic interchain interactions by increasing the oxidation
state of MnO while the reverse process can be induced by thermal reduction.
The underlying structural change is revealed by low-energy electron diffraction
intensity data (LEED-IV) analysis. Density functional theory calculations
suggest that the magnetic transition may be caused by a significant increase of
the Heisenberg exchange upon oxidation.Comment: 6 pages, 3 figure
Epitaxial Cobalt Oxide Films with Wurtzite Structure on Au(111)
Several-nanometer-thick, closed, and epitaxial cobalt(II) oxide films with wurtzite crystal structure (w-CoO) are grown on Au(111) and their structural and electronic properties analyzed. The structural quality of the (Formula presented.) oriented, oxygen-terminated, and unreconstructed films allow the application of surface-science methods to unravel the properties of this unusual polymorph of CoO and may pave the way for future thin-film applications. An experimental structural analysis by low-energy electron diffraction (LEED-IV) is presented with an excellent agreement between measured and calculated intensity spectra expressed by a Pendry R-factor of (Formula presented.) and few-picometer error bounds in the parameter values. Using scanning tunneling spectroscopy (STS) the bandgap of the semiconducting films is found to be 1.4 ± 0.2 eV. Ultraviolet photoelectron spectroscopy (UPS) confirms the presence of a gap and the position of the Fermi level (E F). The structural results of density functional theory calculations using (hybrid) functionals to treat electron correlations and van der Waals forces agree well with the experimentally determined structure of the antiferromagnetic w-CoO films. In contrast to generalized gradient approximation (GGA)+U calculations, the Heyd–Scuseria–Ernzerhof hybrid functional reproduces the semiconducting nature correctly and predicts surface states in the gap which might pin E F in agreement with STS and UPS
Orbital-driven Rashba effect in a binary honeycomb monolayer AgTe
The Rashba effect is fundamental to the physics of two-dimensional electron
systems and underlies a variety of spintronic phenomena. It has been proposed
that the formation of Rashba-type spin splittings originates microscopically
from the existence of orbital angular momentum (OAM) in the Bloch wave
functions. Here, we present detailed experimental evidence for this OAM-based
origin of the Rashba effect by angle-resolved photoemission (ARPES) and
two-photon photoemission (2PPE) experiments for a monolayer AgTe on Ag(111).
Using quantitative low-energy electron diffraction (LEED) analysis we determine
the structural parameters and the stacking of the honeycomb overlayer with
picometer precision. Based on an orbital-symmetry analysis in ARPES and
supported by first-principles calculations, we unequivocally relate the
presence and absence of Rashba-type spin splittings in different bands of AgTe
to the existence of OAM
Surface structure and stacking of the commensurate charge density wave phase of
By quantitative low-energy electron diffraction (LEED) we investigate the extensively studied commensurate charge density wave (CDW) phase of trigonal tantalum disulphide (1T−TaS2), which develops at low temperatures with a (13×13)R13.9∘ periodicity. A full-dynamical analysis of the energy dependence of diffraction spot intensities reveals the entire crystallographic surface structure, i.e., the detailed atomic positions within the outermost two trilayers consisting of 78 atoms as well as the CDW stacking. The analysis is based on an unusually large data set consisting of spectra for 128 inequivalent beams taken in the energy range 20–250 eV and an excellent fit quality expressed by a best-fit Pendry R factor of R=0.110. The LEED intensity analysis reveals that the well-accepted model of star-of-David-shaped clusters of Ta atoms for the bulk structure also holds for the outermost two TaS2 trilayers. Specifically, in both layers the clusters of Ta atoms contract laterally by up to 0.25 Å and also slightly rotate within the superstructure cell, causing respective distortions as well as heavy bucklings (up to 0.23 Å) in the adjacent sulfur layers. Most importantly, our analysis finds that the CDWs of the first and second trilayers are vertically aligned, while there is a lateral shift of two units of the basic hexagonal lattice (6.71 Å) between the second and third trilayers. The results may contribute to a better understanding of the intricate electronic structure of the reference compound 1T−TaS2 and guide the way to the analysis of complex structures in similar quantum materials