Sm Atoms Research Articles

Phase formation and magnetic properties of Co-rare earth magnetic films

Co–Sm and Co–Pr films were deposited by dc magnetron sputtering. Transmission electron microscopy and magnetic measurement were used to study the microstructure and magnetic property relationship. The nanostructure of the as-deposited Co 19 at. % Sm films consists of two phases: the amorphous phase and the crystallite phase. Upon annealing at 600 °C, the Co5Sm phase with the Cu5Ca structure, having grain size of about 20 nm, is obtained along with high coercivity (45 kOe). The as-deposited Co 22 at. % Sm films also have nanostructure similar to the Co 19 at. % films except the volume fraction of the crystallite is reduced. This is related to the concentration of Sm which promotes the formation of the amorphous phase. A new metastable phase Co3Sm is formed upon annealing of the Co 22 at. % Sm film at 500 °C. This phase has the DO19 structure in which the Sm atoms take ordered positions of a triangular pattern in the close-packed planes. A relatively high coercivity value of 29 kOe was obtained from this phase. The as-deposited Co–Pr films show mainly an amorphous phase. Upon annealing at 500 °C for 20 min, Co2Pr with the Mg2Cu-type structure was identified in the Co 35 at. % Pr film. Two phases were identified in the Co 16 at. % Pr films. Coercivities up to 3.1 kOe were achieved in these films.

Formation of modified TbCu 7 and Th 2Zn 17 type structures during annealing of mechanical-alloyed Sm–Fe powders

Compounds with the nominal composition near Sm 2Fe 17 were prepared by mechanical alloying starting from the elemental powders and subsequent annealing at temperatures, T A, between 600°C and 900°C. For crystal structure investigations of the non-equilibrium phases formed at various temperatures, XRD methods with following Rietveld analysis were applied. For T A between 600°C and 750°C a modified TbCu 7-type structure of space group P6/ mmm was found, in which the Fe(2 c) site is replaced by the partially (1/3) and randomly occupied Fe(6 l) site. Its approximate composition is SmFe 8.8–9.0. For T A between 800°C to 900°C a disordered modified Th 2Zn 17 structure (space group R 3 ̄ m) was found that is formed by introducing additional randomly occupied Fe (6 c) and Sm(3 a) positions, respectively. The degree of order of Sm atoms and Fe-dumbbells along the c-direction increases with increasing T A. A decrease in the Fe concentration in the cell is observed for increasing T A. The completely ordered stoichiometric Th 2Zn 17-type structure could not be reached by annealing samples prepared from the ball-milled elemental powders.

Magnetic Properties of (Y1-xSmx)2Co17 Compounds

The influence of Sm atoms on the magnetic properties of (Y1-xSmx)2Co17 has been studied by means of NMR and magnetic measurements. The easy direction of magnetization at 4.2 K changes from the c plane for x<0.1 to the c axis for x>0.15. The NMR study has shown that the change of the magnetic anisotropy is explained by the increased contribution to the magnetic anisotropy from Co atoms. In the analysis of the 59Co hyperfine fields at each site, we assumed that the Co moments at respective sites have the same magnitude and that the transferred hyperfine field from the Sm spins is proportional to the Sm concentration.

Novel, Highly Symmetrical Halogen-Centered Polynuclear Lanthanide Complexes: [Cp6Yb6Cl13]− and [Cp12Sm12Cl24

If THF is removed from the complexes [CpLnCl2(thf)3] (Cp=C5H5, Ln=Sm, Yb), halogen-centered polynuclear complexes are formed. [{CpSmCl2}12] displays an icosahedral arrangement of the 12 Sm atoms with 20 Cl atoms in the “outer envelope” and four further Cl atoms within the icosahedron (see structure on the right). The partially desolvated [CpYbCl2]⋅1/3 THF consists of trinuclear cations [Cp3Yb3Cl5(thf)3]+ and octahedral anions [Cp6Yb6Cl13]−.

Initial stages in the Sm-Si(111) interface formation

The initial stages in the formation of the Sm-Si(111) interface have been studied by thermal desorption, atomic beam modulation, and low-energy-electron-diffraction spectroscopy. The structure of adsorbed films and samarium silicide films, as well as the Sm atom desorption kinetics have been investigated within a broad range of surface coverages and temperatures. The activation energy of desorption from the thermally most stable 3×2 submonolayer structure, as well as the binding energy of a single samarium atom with the substrate, have been measured. The temperature of the onset of silicide decomposition and the activation energy of this process have been determined. It is shown that the Sm-Si(111) interface forms by a mechanism close to that of Stransky-Krastanov.

Structural investigation of Ba6−3xLn8+2xTi18O54 (x = 0.27, Ln = Sm) by single crystal x-ray diffraction in space group Pnma(No. 62)

Single crystals of barium samarium titanium oxide Ba6−3xSm8+2xTi18O54 (x = 0.27) have been synthesized and studied using x-ray diffraction. Superstructure reflections, which cause a doubling of the cell along the short axis, were taken into account and the refinement was conducted in the orthorhombic space group Pnma. Unit cell parameters from single crystal x-ray diffraction were a = 22.289(1), b = 7.642(1), and c = 12.133(1) Å. Refinement on F resulted in R1 = 5.37% for 1410 Fo &gt; 4σ with the thermal parameters of the Sm and Ba atoms refined anisotropically and the thermal parameters of the Ti and O atoms refined isotropically. The structure is made up of a network of corner sharing TiO6−2 octahedra creating rhombic (perovskite-like) and pentagonal channels. The two pentagonal channels are fully occupied by Ba atoms. The refinement suggests that one rhombic channel is fully occupied by Sm atoms (Sm3/Sm4), one rhombic channel is partially occupied by Sm atoms (100% Sm1/86.25% Sm5), and one rhombic channel is shared by BaySm atoms (59.25% Ba3/40.75% Sm2), resulting in a formula of Ba10.38Sm17.08Ti36O108 with Z = 1. The above site occupancies differ from the site occupancies previously reported in the literature for refinements conducted with the short axis approximately equal to 3.8 Å.

A dinuclear cyano-bridged complex based on hexacyanoferrate(III) and samarium(III) nitrate: synthesis and crystal structure

A new complex, [Sm(DMF)4(H2O)4Fe(CN)6]·H2O (DMF = N, N-dimethylformamide), has been synthesized and characterized by X-ray single crystal structure and thermogravimetric analyses. The complex crystallizes in the P21/n space group, with lattice parameters a = 17.583(4) A, b = 8.870(2) A, c = 19.845(6) A, β = 95.98(3)°, V = 3078(1) A3, D x = 1.679 Mg m−3, D m = 1.65(1) Mg m−3, Z = 4. The molecular structure shows that a cyano-bridged bimetallic structure is obtained. The Sm atom is coordinated by eight oxygen atoms of four water molecules and four DMF molecules and one nitrogen atom of the bridging cyanide ligand. The iron atom assumes approximately an octahedral environment surrounded by six CN ligands. The hydrate water molecule is hydrogen-bonded to one of the O atoms bound to Sm. Each terminal CN ligand of the Fe(CN) 6 3− entity is hydrogen-bonded to some O atoms of water molecules. An infrared spectrum is also reported.

Coadsorption of Carbon Monoxide and Samarium on the Ru(001) Surface

The effect of preadsorbed Sm atoms on CO adsorption has been studied over the Ru(001) surface, employing temperature-programmed desorption and photoemission spectroscopy. It was found that the presence of Sm atoms yields more tightly bound CO species compared with CO molecules adsorbed on clean Ru sites. The tightly bound CO species interact attractively with coadsorbed Sm atoms, and this attractive interaction leads to a formation of two-dimensional Sm + CO coadsorption islands on the surface. It seems that the Sm + CO coadsorption island gives additional adsorption sites, which interact very weakly with CO located upon the island. Upon heating the Sm + CO coadsorbed layer, the tightly bound CO located inside the Sm + CO island subsequently dissociated and oxidized Sm to form two-dimensional compounds.

Adsorption of CO on Sm-modified Ru(001): formation of unusual adsorption states of CO

The adsorption behavior of CO over a Sm-preadsorbed Ru(001) surface was studied using photoemission spectroscopy. In addition to the usual CO adsorption upon Ru(001), both more tight and very weak adsorption states of CO appeared at about 105 K. The weakly bound CO was found to yield exceedingly high binding energy (BE) emissions in both core and valence regions compared to CO adsorption on metal surfaces. It is likely that the tightly bound CO attractively interacts with the Sm atom, resulting in the formation of Sm + CO islands over the Ru(001) substrate. This two-dimensional Sm + CO composite produces an adsorption site for the weakly bound state of the CO molecule.

Novel Heteroleptic Samarium(II) Complexes Bearing both Aryloxide and Pentamethylcyclopentadienide Ligands

Reaction of (C5Me5)2Sm(THF)2 with 1 equiv of ArOH (Ar = C6H2tBu2-2,6-R-4, R = H, Me, tBu) or Sm(OAr)2(THF)3 in toluene gave almost quantitatively the corresponding heteroleptic unsolvated dimeric Sm(II) complexes [(C5Me5)Sm(μ-OAr)]2 (Ar = C6H2tBu2-2,6-R-4, R = H (1a), Me (1b), tBu (1c)). These heteroleptic complexes are stable in toluene solution and did not undergo ligand redistribution. Addition of 4 equiv of hexamethylphosphoric triamide (HMPA) to a THF solution of 1a−c afforded the corresponding HMPA-coordinated monomeric complexes (C5Me5)Sm(OAr)(HMPA)2 (2a−c) in 90−94% isolated yields. Air-oxidation of 1c yielded an orange-red Sm(III) complex, (C5Me5)2Sm(OAr) (3, Ar = C6H2tBu3-2,4,6), in which an agostic interaction between the central Sm(III) ion and an ortho-tBu methyl group was observed. Reaction of 1a−c with 2 equiv of C5Me5K in THF yielded the polymeric Sm(II) complexes [(μ,η5-C5Me5)Sm(OAr)(μ,η5-C5Me5)K(THF)2]∞ (4a−c), in which the “(C5Me5)K(THF)2” unit acted as a neutral coordination ligand. Metathesis reaction of (ArO)2Sm(THF)3 with C5Me5K or (C5Me5)2Sm(THF)2 with ArOK also gave 4a−c in excellent yields. In the solid state, the ArO ligand of 4b (Ar = C6H2tBu2-2,6-Me-4) was severely bent toward the central Sm atom (∠Sm−O−Ar 126.7(5)°) and an agostic interaction between the Sm atom and an ortho-tBu methyl group of the ArO ligand was observed. Reaction of 4a−c with 2 equiv of HMPA in THF yielded 2a−c in 90−95% isolated yields.

Influence of parity-forbiddenness in the onset of mixed valence state in Sm1−x GdxS

The electronic structure of Sm and Gd in Sm1−xGdxS has been experimentally studied by the x-ray shift method. Besides the well known strong increase of Sm valence at x≈0.15 (associated with the electronic transition to the mixed valence state), a decrease of Sm valence for x⩾0.9 has been observed for the first time. This phenomenon is explained as due to the 4f-5d hybridization on neighboring Sm atoms involved in the onset of the mixed valence state, and is interpreted as a manifestation of parity violation forbiddenness.

In Situ EXAFS Characterisation of the Synthesis of Polynuclear Chloroniobates from Sm Atom Reactions with Niobium Pentachloride

A new method to prepare solid state chlorometallates by reductive dechlorination of solvated niobium pentachloride with vaporisation of nominally free atoms of samarium is described. Products were prepared in an original set-up by evaporation of samarium into a mixed toluene solution of NbCl 5 , at 180 K. The local order around the Nb atoms was probed by EXAFS spectroscopy at the Nb K edge, using an in situ cryostat coupled to the metal vapour oven, in order to better understand the condensation mechanisms. These in situ measurements confirm our previous ex situ EXAFS studies with solid state products obtained by Sm vaporisation: condensation of NbCl 5 by face-sharing octahedra.

Infrared transmission study of lanthanide füllendes SmxC60 prepared by metal vapor synthesis

Lanthanide füllende SmxC60 films were prepared by metal vapor synthesis and the valence state of the C60 cage in the films was investigated by infrared transmission spectroscopy. Three films with different doping contents of Sm showed red-shift frequencies of Fiu(4) at 1347, 1362 and 1392 (1411) cm−1, respectively, indicating that the major phase with corresponding valence state n≈ −5, −3 and −1 might exist in the films. The other major additional feature of activated pentagonal pinch mode Ag(2) was observed at 1445 or 1448 cm−1 in the films, which suggested that the Sm atoms might bond to the five-membered ring of the C60 cage and ferrocene-like SmxC60 complexes might be formed.

Photoelectron spectroscopy and scanning tunneling microscopy studies of the initial growth of the Sm-on-Pt(100) interface.

The Sm-on-Pt(100) overlayer system has been studied by photoelectron spectroscopy, scanning tunneling microscopy (STM), and low-energy electron diffraction (LEED) at room temperature. As Sm overlayers were evaporated onto the Pt(100)-hex-R0.7\ifmmode^\circ\else\textdegree\fi{} reconstructed single-crystal surface, the initial growth of the interface was studied. Photoelectron spectroscopy and LEED indicate that Sm and Pt has formed an intermixed, disordered phase in the surface. The Pt 4f core-level spectra indicate the existence of an unresolved surface component that disappears with Sm deposition. For all Sm coverages (0.3--20 \AA{}), trivalent Sm was observed. Some divalent Sm was seen after \ensuremath{\sim}20 \AA{} Sm deposition, and was believed to stem from Sm atoms at the surface. LEED and STM show that Sm adsorption induces a local lifting of the hexagonal reconstruction. The first monolayer of the Sm-Pt compound grows as long (100--1000 \AA{}), narrow (30--50 \AA{}) islands directed along the direction of longest periodicity of the reconstructed structure. At the same time, the uncovered areas display the hexagonally reconstructed structure. The Sm-Pt islands are seen to be centered on the elevated ridges of the reconstruction. There are no indications of preferential nucleation centers, such as steps or defects. Two effects are discussed to contribute simultaneously to the observed island shape: (1) an anisotropic Sm diffusion, favoring diffusion along the reconstruction ridges, and (2) lifting of the reconstruction along the elevated ridges is the energetically favorable process, due to lower Pt-Pt coordination in these on-top sites. \textcopyright{} 1996 The American Physical Society.

Synthesis and x-ray structure of the first lanthanide 2-mercaptopyridine n-oxide complex, tris-(1-hydroxy-2(1H)-pyridinethionato-o, s) bis [sulfinylbis (methane)] samarium(III)

The first crystallographically characterized 2-mercaptopyridine N-oxide (HPT) complex of samarium was obtained by the reaction of Sm(OAc)3 with NaPT in dimethyl sulfoxide (DMSO). The 2-mercaptopyridine N-oxide ligand generates an eight-coordinate complex, Sm(PT)3(DMSO)2, in which the solvent molecules, DMSO, take part in coordination to Sm. The Sm atom has a distorted dodecahedron with the Sm-S and Sm-O bond distances of 2.878(2)-2.916(2) and 2.359(5)-2.440(4) A, respectively. Copyright © 1996 Elsevier Science Ltd

A synchrotron X-ray study of the electron density in SmFeO3

Structure factors for small, hydrothermally grown samarium orthoferrite, SmFeO3, were measured with focused λ = 0.7 Å synchrotron radiation. Approximate high symmetry in the Δρ images indicates that cations deform the electron density far more strongly than the O atoms. The most obvious effect is on distribution of the Fe atoms. The influence of the nearest low-symmetry (Cs ) O coordination on the electron density of the Sm cation is weak by comparison with that of the Sm–Fe interactions, as is illustrated by the high symmetry of the Δρ map near the Sm atom. The Sm–Fe interactions appear to affect the magnetic ordering and spin configuration of the Fe atoms. Space group Pnma, orthorhombic, Mr = 254.20, a = 5.6001 (3), b = 7.7060 (7), c = 5.3995 (6) Å, V = 233.01 (4) Å3, Z = 4, Dx = 7.246 Mg m−3, μ 0.7 = 28.5 mm−1, F(000) = 448, T = 293 K, R = 0.017, wR = 0.021, S = 3.83 (8) for 1329 unique reflections.

Crystal structure of Serratia protease, a zinc-dependent proteinase from Serratia sp. E-15, containing a beta-sheet coil motif at 2.0 A resolution.

The crystal structure of Serratia protease from Serratia sp. E-15 was solved by the single isomorphous replacement method supplemented with anomalous scattering effects from both the Zn atom in the native crystal and the Sm atom in the derivative crystal, and refined at 2.0 A resolution to a crystallographic R-factor of 0.194. The enzyme consists of N-terminal catalytic and C-terminal beta-sandwich domains, as observed in alkaline protease from Pseudomonas aeruginosa IFO3080. The catalytic domain with a five-stranded antiparallel beta-sheet and five alpha-helices shares a basically common folding topology with those of other zinc metalloendoproteases. The catalytic zinc ion at the bottom of the active site cleft is ligated by His176, His180, His186, Tyr216, and a water molecule in a distorted trigonalbipyramidal manner. The C-terminal domain is a beta-strand-rich domain containing eighteen beta-strands and a short alpha-helix, and has seven Ca2+ ions bound to calcium binding loops. An unusual beta-sheet coil motif is observed in this domain, where the beta-strands and calcium binding loops are alternately incorporated into an elliptical right-handed spiral so as to form a two-layer untwisted beta-sandwich structure. The Ca2+ ions in the C-terminal domain seem to be very important for the folding and stability of the beta-sheet coil structure.

Photoemission study of the Sm/Si(100)2×1 interface

The behavior of interface formed by growing thin Sm film on the Si(100)2×1 substrate at room temperature and its temperature evolution has been investigated by core-level and valence-band photoemission using synchrotron radiation. The experimental results show the existence of distinct stages corresponding to chemisorption and agglomeration of Sm atoms(coverage ϑ<0.5ML), reactive interdiffusion(0.5< ϑ<4–6ML), and growth of metallic Sm. Compared to Si(111)7×7 the reactivity of Sm on the Si(100)2×1 substrate is enhanced and a greater tendency for interdiffusion of Sm and Si is observed. Like on Si(111), a multiphase interface is formed but less stable. After being annealed, this phase disappears gradually. When the annealing temperature gets up to 1000 °C, an original 2×1 LEED patterns appear again on the surface. Together with a model, the interface formation and the interface profile is discussed in detail in the text.

SRPES STUDY OF THE Sm/Si(100) INTERFACE FORMATION AND ELECTRONIC STRUCTURES

The behavior of interface formed by growing this Sm film on the Ｓｉ（１００）２×１ substrate at room temperature has been investigated by cove level and valence band photoemission using synchrotron radiation. The experimental results show the existence of distinct stages corresponding to chemisorption and agglomeration of Sm atoms（coverage Θ＜０.５ＭＬ）,reactive interdiffusion （０.５ＭＬ≤Θ≤４—６ＭＬ）, and growth of metallic Sm. Compared to Ｓｉ（１１１）７×７ the reactivity of Sm on the Ｓｉ（１００）２×１ substrate is enhanced and a greater tendency for interdiffusion of Sm and Si is observed. Also we have discussed the interface formation and the interface profile carefully.

Phase equilibria at 1150°C in the Co-rich alloys SmCoZr and structure of the 1:7 phase

In the concentration range 75–100 at.% Co, the isothermal section at 1150°C of the system SmCoZr is determined experimentally. The following features are evidenced: a very small Sm solubility in Co, Zr2Co11, and Zr6Co23, an extended Zr for Sm substitution rate in SmCo3, Sm2Co7 and Sm5Co19, and a significant Zr solubility in SmCo5 and Sm2Co17 that induces the existence of a continuous ternary single phase 1:7. On the basis of the lattice parameter data, the formation of this phase by the substitution of Co dumbbells and/or Sm atoms for Zr atoms is proposed.