Sm Atoms Research Articles

Exotic electronic structures of SmxCe3-xOy (x = 0-3; y = 2-4) clusters and the effect of high neutral density of low-lying states on photodetachment transition intensities.

Lanthanide (Ln) oxide clusters have complex electronic structures arising from the partially occupied Ln 4f subshell. New anion photoelectron (PE) spectra of SmxCe3-xOy- (x = 0-3; y = 2-4) along with supporting results of density functional theory (DFT) calculations suggest interesting x and y-dependent Sm 4f subshell occupancy with implications for Sm-doped ionic conductivity of ceria, as well as the overall electronic structure of the heterometallic oxides. Specifically, the Sm centers in the heterometallic species have higher 4f subshell occupancy than the homonuclear Sm3Oy-/Sm3Oy clusters. The higher 4f subshell occupancy both weakens Sm-O bonds and destabilizes the 4f subshell relative to the predominantly O 2p bonding orbitals in the clusters. Parallels between the electronic structures of these small cluster systems with bulk oxides are explored. In addition, unusual changes in the excited state transition intensities, similar to those observed previously in the PE spectra of Sm2O- and Sm2O2- [J. O. Kafader et al., J. Chem. Phys. 146, 194310 (2017)], are also observed in the relative intensities of electronic transitions to excited neutral state bands in the PE spectra of SmxCe3-xOy- (x = 1-3; y = 2, 4). The new spectra suggest that the effect is enhanced with lower oxidation states and with an increasing number of Sm atoms, implying that the prevalence of electrons in the diffuse Sm 6s-based molecular orbitals and a more populated 4f subshell both contribute to this phenomenon. Finally, this work identifies challenges associated with affordable DFT calculations in treating the complex electronic structures exhibited by these systems, including the need for a more explicit treatment of strong coupling between the neutral and PE.

Spatially-correlated site occupancy in the nonstoichiometric meta-stable [formula omitted]-Al60Sm11 phase during devitrification of Al-10.2 at.% Sm glasses

A metastable ε-Al60Sm11 phase appears during the initial devitrification of as-quenched Al-10.2 at.% Sm glasses. The ε phase is nonstoichiometric in nature since Al occupation is observed on the 16f Sm lattice sites. Scanning transmission electron microscopic images reveal profound spatial correlation of Sm content on these sites, which cannot be explained by the “average crystal” description from Rietveld analysis of diffraction data. Thermodynamically favorable configurations, established by Monte Carlo (MC) simulations based on a cluster-expansion model, also give qualitatively different correlation functions from experimental observations. On the other hand, molecular dynamics simulations of the growth of ε-Al60Sm11 in undercooled liquid show that when the diffusion range of Sm is limited to ∼4 Å, the correlation function of the as-grown crystal structure agrees well with that of the scanning transmission electronic microscopy (STEM) images. Our results show that kinetic effects, especially the limited diffusivity of Sm atoms plays the fundamental role in determining the nonstoichiometric site occupancies of the ε-Al60Sm11 phase during the crystallization process.

Room temperature ferromagnetic and optical properties of rare earth Sm-doped tris(8-hydroxyquinoline) gallium thin films

The development of room temperature organic magnets is long viewed as great challenge in chemistry, physics, materials science, and spintronics. Here, room temperature ferromagnetic properties of rare earth Sm-doped tris(8-hydroxyquinoline) gallium (GaQ3) molecular thin films prepared by thermally co-evaporating Sm metals and GaQ3 powders were reported. X-ray photoelectron spectrometer, Fourier transform infrared spectroscopy and density functional theory analysis suggest that the doped Sm atom bonds with N atoms on different hydroxyquinoline ligands. The room temperature ferromagnetism is attributed to the extremely large energy difference (594meV) between the ferromagnetic ground state and the antiferromagnetic state. Furthermore, photoluminescence experiments show that the films emit green light at room temperature. Our experiments may be helpful for the development of molecular ferromagnetic optoelectronic materials for the use of novel multifunctional optoelectronic and spintronic devices.

A comparative study of Sm networks in Al-10 at.%Sm glass and associated crystalline phases

The Al–Sm system is selected as a model system to study the transition process from liquid and amorphous to crystalline states. In recent work, we have shown that, in addition to long-range translational periodicity, crystal structures display well-defined short-range local atomic packing motifs that transcends liquid, amorphous and crystalline states. In this paper, we investigate the longer range spatial packing of these short-range motifs by studying the interconnections of Sm–Sm networks in different amorphous and crystalline samples obtained from molecular dynamics simulations. In our analysis, we concentrate on Sm–Sm distances in the range ~5.0–7.2 Å, corresponding to Sm atoms in the second and third shells of Sm-centred clusters. We discover a number of empirical rules characterising the evolution of Sm networks from the liquid and amorphous states to associated metastable crystalline phases experimentally observed in the initial stages of devitrification of different amorphous samples. As direct simulation of glass formation is difficult because of the vast difference between experimental quench rates and what is achievable on the computer, we hope these rules will be helpful in building a better picture of structural evolution during glass formation as well as a more detailed description of phase selection and growth during devitrification.

Study of the Radiation Resistance of Endohedral Fullerenes of Rare-Earth Elements and Their Water-Soluble Derivatives

Endohedral metallofullerenes Me@C2n (n = 30–50), their hydroxylated derivatives Me@C2n(OH)38–40 (Me = Tm, Ho, Eu, Sm, Co), and fullerenol С60(OH)38 have been synthesized The radiation resistance of these structures under irradiation in reactor by thermal and fast neutron fluxes in the fluence range of 1018–1019 cm–2 (cadmium ratio of ~10) has been analyzed. Endofullerenols are shown to be more stable in comparison with initial endohedral fullerenes; the molecules containing Eu and Sm (atoms characterized by the largest slow-neutron absorption cross section) turned out to be most stable. The mechanism of the formation of secondary Eu and Sm endofullerenols is discussed taking into account the neutron capture and emission of γ quanta by excited nuclei, which acquire the recoil energy.

Crystal and Electronic Structure of (Y,Pr) x Sm1−x BO3 Oxide

The effects of Y and Pr substitution on the electronic and crystal structure of triclinic SmBO3 have been investigated using x-ray diffraction (XRD) analysis and x-ray absorption fine-structure spectroscopy. Polycrystalline structure was observed on substitution of Y3+ and Pr4+ ions with Sm3+ coordination. Yttrium-substituted samples were found to contain BO3 ligands around Sm atoms, while the crystal structure of YBO3 presented hexagonal geometry, not preserving the triclinic crystal structure. Also, praseodymium ions (Pr4+) formed isolated Pr2B5 crystal structure by distorting some BO3 ligands. Moreover, electronic structure studies revealed that 4f levels of Sm and Pr were inactive in bonding interaction and did not support strong coupling between neighboring Sm and Y/Pr atoms.

Evolution of magnetic phases inSmCrO3: A neutron diffraction and magnetometric study

The classical belief about the mechanism of spin reorientation phase transition (SRPT) and ground-state magnetic structure in ${\mathrm{SmCrO}}_{3}$ has become intriguing because of inconsistent bulk magnetization observations. The presence of highly neutron-absorbing Sm atom has so far evaded the determination of microscopic magnetic structure. In the present report, we have utilized very high-energy ``hot neutrons'' to overcome the Sm absorption and to determine the thermal evolution of magnetic configurations. Unambiguously, three distinct phases are observed: the uncompensated canted antiferromagnetic structure ${\mathrm{\ensuremath{\Gamma}}}_{4}({G}_{x},{A}_{y},{F}_{z};{F}_{z}^{R})$ occurring below the N\'eel temperature (${T}_{N}=191$ K), the collinear antiferromagnetic structure ${\mathrm{\ensuremath{\Gamma}}}_{1}({A}_{x},{G}_{y},{C}_{z};{C}_{z}^{R})$ occurring below 10 K, and a nonequilibrium configuration with cooccurring ${\mathrm{\ensuremath{\Gamma}}}_{1}$ and ${\mathrm{\ensuremath{\Gamma}}}_{4}$ phases in the neighborhood of the SRPT (10 K $\ensuremath{\le}T\ensuremath{\le}$ 40 K). In differing to the earlier predictions, we divulge the SRPT to be a discontinuous transition where chromium spins switch from the $a\ensuremath{-}b$ crystallographic plane to the $b\ensuremath{-}c$ crystallographic plane in a discrete manner with no allowed intermediate configuration. The canting angle of chromium ions in the $a\ensuremath{-}b$ plane is unusually not a thermal constant, rather it is empirically discerned to follow exponential behavior. The competition between magnetocrystalline anisotropy and free energy derived by isotropic and antisymmetric exchange interactions between different pairs of magnetic ions is observed to govern the mechanism of SRPT.

Surface electronic structure of SmB6(111)

Samarium hexaboride (SmB6) is the most extensively studied candidate of topological Kondo insulators. To clarify the topological origin of metallic surface states observed on the SmB6(001) surfaces, we studied the surface electronic structure of SmB6 on the other surface orientation, SmB6(111). Although the SmB6(111) surface cannot be obtained by cleaving, we successfully obtained the well-defined clean surface by high-temperature annealing of the mechanically polished single crystal of SmB6(111) in an ultra-high vacuum. The valence band spectra obtained by photoelectron spectroscopy with the bulk and surface-sensitive incident photon energies imply that the surface is covered with B6 cluster without Sm atoms.

Electronic states in the pressure-induced magnetically ordered phase in SmB6

We have carried out the high-pressure measurement of X-ray absorption spectroscopy on the intermediate valence compound SmB6 which shows magnetic ordering as well as an insulator-metal transition at critical pressure Pc ∼ 10 GPa. The valence of Sm atom at room temperature increases with increasing pressure, however it is far below a trivalent state at Pc. In contrast to cases of pressure-induced nonmagnetic-magnetic transition in Yb compounds, which mostly occurs in the scheme of well localized 4f electrons, the present observation suggests that electronic system in SmB6 still possesses strong delocalized characters at Pc.

Valence instability in the bulk and at the surface of the antiferromagnet SmRh2Si2

Using resonant angle-resolved photoemission spectroscopy and electron band-structure calculations, we explore the electronic structure and properties of Sm atoms at the surface and in the bulk of the antiferromagnet SmRh2Si2. We show that the Sm atoms reveal weak mixed-valent behavior both in the bulk and at the surface. Although trivalent 4f emission strongly dominates, a small divalent 4f signal near the Fermi energy can be clearly resolved for surface and bulk Sm atoms. This behavior is quite different to most other Sm-based materials which typically experience a surface valence transition to a divalent state of Sm atoms at the surface. This phenomenon is explained in analogy to the isostructural Ce compound, where strong 4f hybridization stabilizes mixed-valent ground state both in the bulk and at the surface, and which were described in the light of the single-impurity Anderson model. Implications for other RERh2Si2 (RE = rare-earth elements) compounds are discussed.

Electronic structure and optical properties of β-RbSm(MoO4)2 from spin polarization calculations: DFT+U

We explored the influence of the inclusion of spin polarization on the energy band gap of β-RbSm(MoO4)2. Calculations explored that the appearance of Sm-4f states at the conduction band minimum (CBM) of the spin-up case causes a significant influence on ground state properties of β-RbSm(MoO4)2. The total and partial densities of states confirm the existence of Sm-4f states in the CBM of the spin-up case. The partial densities of states exhibit a strong hybridization between some states which may lead to the formation of covalent bonds. The valence band maximum (VBM) and the CBM are located at the center of first Brillouin zone (Γ), resulting in a direct band gap for both of majority spin (↑) and minority spin (↓). The values of the band gap are 3.01 eV (↑) and 3.78 eV (↓). The all-electron full potential linear augmented plane wave (FPLAPW+lo) method within the generalized gradient approximation plus the Hubbard Hamiltonian (GGA+U) were used. We have applied U on 4f orbital of Sm atoms and 4d orbital of Mo atoms. We have taken a careful look at the electronic charge density distribution to visualize the charge transfer and the chemical bonding characters. The calculated bond lengths show very good agreements with the measured ones. The optical properties were calculated to seek a deep insight into the electronic structure. It has been found that below λ = 450 nm β-RbSm(MoO4)2 exhibits a positive uniaxial anisotropy, while at λ = 450 nm and above, the crystal exhibits a negative uniaxial anisotropy.

Structural and antiferromagnetic properties of Sm-doped chrysene

The experimental discovery of superconductivity was reported in Sm-doped chrysene with Tc∼5 K, which provides vital material for exploring unique superconducting mechanism of rare-earth metal doped polycyclic aromatic hydrocarbons. Here the crystal, electronic structures and magnetic characteristics of Sm-doped chrysene have been investigated by the first-principles calculation using the generalized gradient approximation (GGA) plus U method, also including van der Waals correction. We find that Sm-doped chrysene with C2/c space group is the most stable where doped Sm atoms stay on the relative middle of chrysene molecules. This material is stabilized at antiferromagnetic ground-state with the metallic feature. The calculated spin magnetic moment of Sm atom indicates that there are two electrons transferring from Sm to chrysene molecule. Within the framework of GGA+U, the C-2p electronic states mainly contribute to the Fermi surface. Electronic correlation effects are significant to understand the superconductivity in Sm-doped chrysene.

The first-principles investigations on magnetic ground-state in Sm-doped phenanthrene

Based on the density functional theory plus the effective Coulomb repulsion U, we have investigated the crystal structure, electronic properties and magnetic characteristics in Sm-doped phenanthrene, recently characterized as a superconductor with Tc∼5−6 Kelvin. Calculated total energies of different magnetic states indicate that Sm-doped phenanthrene is stable at the ferromagnetic ground-state. Considered the strong electronic correlations effect due to the intercalation of Sm-4f electrons, we found that the Sm-4f contributes to the Fermi surface together with C-2p, which is different from K-doped phenanthrene. Compared with alkali-metal-doped phenanthrene, Sm atom has larger local magnetic moment, which suppresses the superconductivity in conventional superconductors. Our results indicate that the electron-electron correlations play an important role in superconductivity of Sm-doped phenanthrene.

First-principles study of Al 2 Sm intermetallic compound on structural, mechanical properties and electronic structure

Abstract The structural, thermodynamic, mechanical and electronic properties of cubic Al2Sm intermetallic compound are investigated by the first-principles method on the basis of density functional theory. In light of the strong on-site Coulomb repulsion between the highly localized 4f electrons of Sm atoms, the local spin density approximation approach paired with additional Hubbard terms is employed to achieve appropriate results. Moreover, to examine the reliability of this study, the experimental value of lattice parameter is procured from the analysis of the TEM image and diffraction pattern of Al2Sm phase in the AZ31 alloy to verify the authenticity of the results originated from the computational method. The value of cohesive energy reveals Al2Sm to be a stable in absolute zero Kelvin. According to the stability criteria, the subject of this work is mechanically stable. Afterward, elastic moduli are deduced by performing Voigt-Reuss-Hill approximation. Furthermore, elastic anisotropy and anisotropy of sound velocity are discussed. Finally, the calculation of electronic density of states is implemented to explore the underlying mechanism of structural stability.

Magnetic and Electronic Properties of Samarium-Doped Phenanthrene from First-Principles Study

Based on the van der Waals density functional theory (DFT), we have studied the crystal structure and magnetic and electronic properties of samarium-doped phenanthrene, a newly discovered aromatic superconductor. For Sm1phenanthrene, we found that the magnetism in the ground state is antiferromagnetic, in good agreement with the experimental measurement. When Hubbard U of 6 eV is considered, the Sm1-A structure becomes an atomic force microscopy (AFM) semiconductor with a gap of 0.12 eV. Including the spin–orbit coupling, the orbital moment of the Sm atom is 2.28 μB with the opposite direction to the spin moment of 5.99 μB. The total moment of 3.7 μB around Sm atoms in Sm-doped phenanthrene is quite distinct to the divalent and trivalent Sm ions in monochalcogenides and samarium hexaboride. The hybridization of Sm 5d and C 2d states results in a relatively strong interaction of metal and molecule in Sm-doped phenanthrene compared with the interaction in K-doped picene and phenanthrene. Our results provide...

Giant effect of Sm atoms on time stability of (NdDy)(FeCo)B magnet

Small amount of Sm additives (∼ 1 -3 at.%) slow down two times relaxation of magnetization of (NdDy)(FeCo)B alloys. Effective freezing of spontaneous relaxation of magnetization is caused by the enhancement of potential barriers of the domain walls. Easy plane single-ion anisotropy of Sm strongly disturbs the potential relief of the domain walls. The experimental results can be used to stabilize hard magnets.

Atomistic simulation of trivalent ions doped in the hexagonal LuMnO3 ferroelectric phase

The interatomic potentials for multiferroic hexagonal LuMnO3 (h-LMO) in its ferroelectric (FE) phase was obtained for empirical fitting procedure and applied to study the effects of a series of trivalent metal and rare-earth dopants on its structural and ferroelectric distortions. The potential parameters found accurately reproduce lattice parameters (error below 0.3%), interatomic distances, pressure effect on the lattice parameters, and tilting angles of the MnO5 polyhedron. We investigated doping at Mn, Lu1 and Lu2 atom sites. It was found that the doped Mn atom site is the most energetically advantageous site for both the metal (Al, Ga, Fe and Cr) and rare-earth (La, Nb, Sm, Eu, Gd, Ho, Er, Yb, Y and Sc) atoms studied. The M-O3/O4 distances decrease when the Mn3+ ion site is doped by trivalent metal ions. The effects on the FE distortion of the material under doping and changes in the tilting angle of the M/MnO5 polyhedron were analyzed.

Structural Stability and Deformation of Solvated Sm@C2(42)-C90 under High Pressure

Solvated fullerenes recently have been shown to exhibit novel compression behaviors compared with the pristine fullerenes. However, less attention has been focused on the large cage endohedral metallofullerenes. Here, we have firstly synthesized solvated Sm@C90 microrods by a solution drop-drying method, and then studied the transformations under high pressure. The pressure-induced structural evolutions of Sm@C90 molecules both undergo deformation and collapse. The band gaps of both samples decrease with increasing pressure. The trapped Sm atom plays a role in restraining the compression of the adjacent bonds. The solvent plays a role in protecting Sm@C90 against collapse in the region of 12–20 GPa, decreasing and postponing the change of band gap. Above 30 GPa, the carbon cages collapse. Released from 45 GPa, the compressed solvated Sm@C90 forms a new ordered amorphous carbon cluster (OACC) structure with metal atoms trapped in the units of amorphous carbon clusters, which is different from the OACC structure formed by compressing solvated C60 and C70. This discovery opens the door for the creation of new carbon materials with desirable structural and physical properties when suitable starting materials are selected.

Structural ordering at solid-liquid interfaces in Al-Sm system: A molecular-dynamics study

The structural ordering at solid-liquid interfaces far from equilibrium is studied with molecular dynamics simulations for the Al-Sm system. Using the van-Hove self-correlation function as the criterion to identify attachment/detachment events that occur at the interface, we are able to determine the time-dependent interface position, and characterize the detailed interfacial structure ordering surrounding the attached atoms. For the interface between an undercooled Al90Sm10 liquid and a metastable cubic structure, the solid induces the crystalline order of the cubic phase in the liquid layers, promoting the continuous growth of the crystal phase. When the same liquid is put in contact with f.c.c. Al, Sm from the liquid can still attach to the solid interface despite its insolubility in the Al lattice. Non-f.c.c. order is revealed surrounding the attached Sm atoms. We show that the local structure ordering at interface is highly correlated to solid packing and liquid ordering.

Intercalation of graphene on iridium with samarium atoms

Intercalation of graphene on Ir (111) with Sm atoms is studied by methods of thermal desorption spectroscopy and thermionic emission. It is shown that adsorption of samarium at T = 300 K on graphene to concentrations of N ≤ 6 × 1014 atoms cm–2 followed by heating of the substrate leads to practically complete escape of adsorbate underneath the graphene layer. At N > 6 × 1014 atoms cm–2 and increasing temperature, a fraction of adsorbate remains on graphene in the form of two-dimensional “gas” and samarium islands and are desorbed in the range of temperatures of 1000–1200 K. Samarium remaining under the graphene is desorbed from the surface in the temperature range 1200–2150 K. Model conceptions for the samarium–graphene–iridium system in a wide temperature range are developed.