646 research outputs found
Moment canting and domain effects in antiferromagnetic DyRhSi
A combined experimental and theoretical study of the layered
antiferromagnetic compound DyRhSi in the ThCrSi-type structure
is presented. The heat capacity shows two transitions upon cooling, the first
one at the N{\'e}el temperature and a second one at
. Using magnetization measurements, we study the canting
process of the Dy moments upon changing the temperature and can assign to the onset of the canting of the magnetic moments towards the
direction away from the axis. Furthermore, we found that the field
dependence of the magnetization is highly anisotropic and shows a two-step
process for . We used a mean-field model to determine the
crystalline electric field as well as the exchange interaction parameters. Our
magnetization data together with the calculations reveal a moment orientation
close to the direction in the tetragonal structure at low temperatures
and fields. Applying photoemission electron microscopy, we explore the (001)
surface of the cleaved DyRhSi single crystal and visualize Si- and
Dy-terminated surfaces. Our results indicate that the Si-Rh-Si surface protects
the deeper lying magnetically active Dy layers and is thus attractive for
investigation of magnetic domains and their properties in the large family of
LnTSi materials
Variation of the character of spin-orbit interaction by Pt intercalation underneath graphene on Ir(111)
Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).-- et al.The modification of the graphene spin structure is of interest for novel possibilities of application of graphene in spintronics. The most exciting of them demand not only high value of spin-orbit splitting of the graphene states, but non-Rashba behavior of the splitting and spatial modulation of the spin-orbit interaction. In this work we study the spin and electronic structure of graphene on Ir(111) with intercalated Pt monolayer. Pt interlayer does not change the 9.3×9.3 superlattice of graphene, while the spin structure of the Dirac cone becomes modified. It is shown that the Rashba splitting of the π state is reduced, while hybridization of the graphene and substrate states leads to a spin-dependent avoided-crossing effect near the Fermi level. Such a variation of spin-orbit interaction combined with the superlattice effects can induce a topological phase in graphene.The work was partially supported by grants of Saint Petersburg State University for scientific investigations (Grants No. 11.38.271.2014, No. 15.61.202.2015 and No.
11.37.634.2013) and Russian Foundation for Basic Research (RFBR) projects (No. 13-02-91327). We acknowledge the financial support of the University of Basque Country UPV/EHU (Grant No. GIC07-IT-756-13), the Departamento de Educacion del Gobierno Vasco, and the Spanish Ministerio de Ciencia e Innovacion (Grant No. FIS2010-19609-C02-01), the Spanish Ministry of Economy and Competitiveness
MINECO (Grant No. FIS2013-48286-C2-1-P), and the Tomsk State University Competitiveness Improvement Program.Peer Reviewe
Electron-phonon coupling in graphene placed between magnetic Li and Si layers on cobalt
Using angle-resolved photoemission spectroscopy (ARPES), we study the electronic structure and electron-phonon coupling in a Li-doped graphene monolayer decoupled from the Co(0001) substrate by intercalation of silicon. Based on the photoelectron diffraction measurements, we disclose the structural properties of the Si/Co interface. Our density functional theory calculations demonstrate that in the studied Li/graphene/Si/Co system the magnetism of Co substrate induces notable magnetic moments on Li and Si atoms. At the same time graphene remains almost nonmagnetic and clamped between two magnetically active atomic layers with antiparallel magnetizations. ARPES maps of the graphene Fermi surface reveal strong electron doping, which may lead to superconductivity mediated by electron-phonon coupling (EPC). Analysis of the spectral function of photoelectrons reveals apparent anisotropy of EPC in the
k space. These properties make the studied system tempting for studying the relation between superconductivity and magnetism in two-dimensional materials
Variation of the character of spin-orbit interaction by Pt intercalation underneath graphene on Ir(111)
The modification of the graphene spin structure is of interest for novel possibilities of application of graphene in spintronics. The most exciting of them demand not only high value of spin-orbit splitting of the graphene states, but non-Rashba behavior of the splitting and spatial modulation of the spin-orbit interaction. In this work we study the spin and electronic structure of graphene on Ir(111) with intercalated Pt monolayer. Pt interlayer does not change the 9.3×9.3 superlattice of graphene, while the spin structure of the Dirac cone becomes modified. It is shown that the Rashba splitting of the π state is reduced, while hybridization of the graphene and substrate states leads to a spin-dependent avoided-crossing effect near the Fermi level. Such a variation of spin-orbit interaction combined with the superlattice effects can induce a topological phase in graphene
Observation of a universal donor-dependent vibrational mode in graphene
Electron-phonon coupling and the emergence of superconductivity in intercalated graphite have been studied extensively. Yet, phonon-mediated superconductivity has never been observed in the 2D equivalent of these materials, doped monolayer graphene. Here we perform angle-resolved photoemission spectroscopy to try to find an electron donor for graphene that is capable of inducing strong electron-phonon coupling and superconductivity. We examine the electron donor species Cs, Rb, K, Na, Li, Ca and for each we determine the full electronic band structure, the Eliashberg function and the superconducting critical temperature Tc from the spectral function. An unexpected low-energy peak appears for all dopants with an energy and intensity that depend on the dopant atom. We show that this peak is the result of a dopant-related vibration. The low energy and high intensity of this peak are crucially important for achieving superconductivity, with Ca being the most promising candidate for realizing superconductivity in graphene
Native and graphene-coated flat and stepped surfaces of TiC
Titanium carbide attracts growing interest as a substrate for graphene growth and as a component of the composite carbon materials for supercapacitors, an electrode material for metal-air batteries. For all these applications, the surface chemistry of titanium carbide is highly relevant and being, however, insufficiently explored especially at atomic level is a subject of our studies. Applying X-ray photoelectron spectroscopy (XPS) to clean (111) and (755) surfaces of TiC, we were able to obtain the detailed spectroscopic pattern containing information on the plasmon structure, shake up satellite, the peak asymmetry and, finally, surface core level shift (SCLS) in C 1s spectra. The latter is essential for further precise studies of chemical reactions. Later on, we studied interface between TiC (111) and (755) and graphene and found the SCLS variation due to strong chemical interaction between graphene and substrate. This interaction is also reflected in the peculiar band structure of graphene probed by angle-resolved photoelectron spectroscopy (ARPES). Based on LEED data the structure is close to (7√3 × 7√3)R30°, with graphene being slightly corrugated. We found that similarly to the graphene on metals, the chemical interaction between graphene and TiC can be weakened by means of intercalation of oxygen atoms underneath graphene.We thank Helmholtz-Zentrum Berlin (HZB) for the allocation of synchrotron radiation beamtimes at the Russian-German and UE112-PGM2 beamlines. The work was financially supported by the Russian Science Foundation (project 16-42-01093). DFT calculations were performed at “Lomonosov” MSU supercomputer.Peer reviewe
Classical and cubic Rashba effect in the presence of in-plane 4f magnetism at the iridium silicide surface of the antiferromagnet GdIr2Si2
We present a combined experimental and theoretical study of the two-dimensional electron states at the iridium-silicide surface of the antiferromagnet GdIr2Si2 above and below the Ned temperature. Using angle-resolved photoemission spectroscopy (ARPES) we find a significant spin-orbit splitting of the surface states in the paramagnetic phase. By means of ab initio density-functional-theory (DFT) calculations we establish that the surface electron states that reside in the projected band gap around the (M) over bar point exhibit very different spin structures which are governed by the conventional and the cubic Rashba effect. The latter is reflected in a triple spin winding, i.e., the surface electron spin reveals three complete rotations upon moving once around the constant energy contours. Below the Ned temperature, our ARPES measurements show an intricate photoemission intensity picture characteristic of a complex magnetic domain structure. The orientation of the domains, however, can be clarified from a comparative analysis of the ARPES data and their DFT modeling. To characterize a single magnetic domain picture, we resort to the calculations and scrutinize the interplay of the Rashba spin-orbit coupling field with the in-plane exchange field, provided by the ferromagnetically ordered 4f moments of the near-surface Gd layer
Colossal magnetoresistance in EuZnP and its electronic and magnetic structure
We investigate single crystals of the trigonal antiferromagnet EuZnP
() by means of electrical transport, magnetization
measurements, X-ray magnetic scattering, optical reflectivity, angle-resolved
photoemission spectroscopy (ARPES) and ab-initio band structure calculations
(DFT+U). We find that the electrical resistivity of EuZnP increases
strongly upon cooling and can be suppressed in magnetic fields by several
orders of magnitude (CMR effect). Resonant magnetic scattering reveals a
magnetic ordering vector of , corresponding to an
-type antiferromagnetic (AFM) order, below . We
find that the moments are canted out of the plane by an angle of about
degrees and tilted away from the [100] - direction
by . We observe nearly isotropic magnetization
behavior for low fields and low temperatures which is consistent with the
magnetic scattering results. The magnetization measurements show a deviation
from the Curie-Weiss behavior below , the temperature below
which also the field dependence of the material's resistivity starts to
increase. An analysis of the infrared reflectivity spectrum at
allows us to resolve the main phonon bands and intra-/interband transitions,
and estimate indirect and direct band gaps of
and ,
respectively, which are in good agreement with the theoretically predicted
ones. The experimental band structure obtained by ARPES is nearly
-independent above and below . The comparison of the theoretical
and experimental data shows a weak intermixing of the Eu 4 states close to
the point with the bands formed by the phosphorous 3 orbitals
leading to an induction of a small magnetic moment at the P sites
Magnetic Dirac semimetal state of (Mn,Ge)BiTe
For quantum electronics, the possibility to finely tune the properties of
magnetic topological insulators (TIs) is a key issue. We studied solid
solutions between two isostructural Z TIs, magnetic MnBiTe and
nonmagnetic GeBiTe, with Z invariants of 1;000 and 1;001,
respectively. For high-quality, large mixed crystals of
GeMnBiTe, we observed linear x-dependent magnetic
properties, composition-independent pairwise exchange interactions along with
an easy magnetization axis. The bulk band gap gradually decreases to zero for
from 0 to 0.4, before reopening for , evidencing topological phase
transitions (TPTs) between topologically nontrivial phases and the semimetal
state. The TPTs are driven purely by the variation of orbital contributions. By
tracing the x-dependent contribution to the states near the fundamental
gap, the effective spin-orbit coupling variation is extracted. As varies,
the maximum of this contribution switches from the valence to the conduction
band, thereby driving two TPTs. The gapless state observed at closely
resembles a Dirac semimetal above the Neel temperature and shows a magnetic gap
below, which is clearly visible in raw photoemission data. The observed
behavior of the GeMnBiTe system thereby demonstrates an
ability to precisely control topological and magnetic properties of TIs
Site- and spin-dependent coupling at the highly ordered h-BN/Co(0001) interface
Using photoelectron diffraction and spectroscopy, we explore the structural and electronic properties of the hexagonal boron nitride (h-BN) monolayer epitaxially grown on the Co(0001) surface. Perfect matching of the lattice parameters allows formation of a well-defined interface where the B atoms occupy the hollow sites while the N atoms are located above the Co atoms. The corrugation of the h-BN monolayer and its distance from the substrate were determined by means of R-factor analysis. The obtained results are in perfect agreement with the density functional theory (DFT) predictions. The electronic structure of the interface is characterized by a significant mixing of the h-BN and Co states. Such hybridized states appear in the h-BN band gap. This allows to obtain atomically resolved scanning tunneling microscopy (STM) images from the formally insulating 2D material being in contact with ferromagnetic metal. The STM images reveal mainly the nitrogen sublattice due to a dominating contribution of nitrogen orbitals to the electronic states at the Fermi level. We believe that the high quality, well-defined structure and interesting electronic properties make the h-BN/Co(0001) interface suitable for spintronic applications.L.V.Ya. acknowledges the RSF (Grant No. 16-42-01093). A.V.T., V.O.S., K.A.B., O.Yu.V., and D.Yu.U. acknowledge St. Petersburg State University for research Grant No. 11.65.42.2017. M.V.K. and I.I.O. acknowledge the RFBR (Grant No. 16-29-06410). C.L. acknowledges the DFG (Grant Nos. LA655-17/1 and LA655-19/1).Peer reviewe
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