Increase In Isomer Shift Research Articles

Hydrogen in amorphous magnetic alloys

Iron-rich Y1−xFex amorphous alloys have been charged electrolytically with hydrogen to an H:Y ratio of approximately 3. The alloys are originally asperomagnetic, with spin freezing temperatures below 110 K, but they become soft ferromagnets on hydrogenation with Curie temperatures in excess of 400 K. The iron moment in a–Y12Fe88 changes from 1.96 to 2.24 μB in the hydride and the isomer shift increases by 0.15 mm/s. However, it appears that the main effect of the hydrogen is to shift a broad, mostly ferromagnetic exchange distribution with some antiferromagnetic interactions to an overwhelmingly ferromagnetic one. This is attributed to dilation of the iron–iron nearest-neighbour distances. By contrast, no significant effects on magnetic moment or exchange were detected on hydrogenating amorphous Fe40Ni38Mo4B18 (Metglas 2826 MB), but the in-plane anisotropy was modified and the soft magnetic properties degraded.

Magnetic properties and155Gd Mossbauer effect in GdCu2and its ternary hydride

The magnetic and crystallographic properties of GdCu2 and its ternary hydride GdCu2Hx have been investigated. Upon hydrogen absorption the crystal structure of GdCu2 changes from orthorhombic (CeCu2-type) to tetragonal (MoSi2-type), accompanied by a lattice expansion of 29%. The uncharged intermetallic compound GdCu2 orders antiferromagnetically (TN=37K). After H2 absorption it becomes ferromagnetic (TC=45K). There is a strong increase in the asymptotic Curie temperature (from theta p=7K to theta p=57K). Studies of the 155Gd Mossbauer effect in the uncharged and charged compounds show that the H2 absorption leads to an increase in isomer shift and in the absolute value of the hyperfine field at 4.2K. Both changes have been discussed in terms of a changing conduction electron concentration.

Experimental study of the amorphous phases of group-IV semiconductors by the119mSn M�ssbauer probe

The amorphous phases of silicon, germanium, and α-tin have been studied by Mossbauer emission spectroscopy on ion-implanted, radioactive119mSn. Amorphous samples have been produced by ion implantations of various elements and by vacuumevaporation techniques. The same well-defined type of complex spectrum is observed for all investigated amorphous samples. These spectra are characterized by an increase in average isomer shift of (0.15±0.03) mm/s, a line broadening of 20±2%, and the same Debye temperature as compared with spectra of substitutional Sn in the respective crystalline host lattices. The spectra are proposed to originate from Sn atoms incorporated substitutionally in the amorphous host with distorted local surroundings. The recrystallization of the amorphous phase upon thermal and laser annealing has been monitored. After appropriate annealing, spectra characteristic of crystalline materials are observed for most samples. An exception are high-dose, inert-gas implanted samples where different complex defects seem to be formed in the annealing process.

Calculation of the119Sn isomer shifts in complexes of tin tetrachloride with organic ligands

The CNDO/2 method in a sp-valence basis has been used to calculate the electronic structure of tin tetrachloride and four complexes of tin tetrachloride with organic ligands. The calculation has given the theoretical values of the /sup 119/Sn isomer shifts, which have been compared with the experimental values. It has been shown that the decrease in the isomer shift taking place on complex formation is due to the decrease in the 5s electron density on the tin atom. For complexes of the type SnCl/sub 4/L/sub 2/, a correlation is observed between the isomer shifts and the ionization potentials of the donor molecule, indicating an increase in the isomer shift with increase in the strength of the donor - acceptor interaction.

Mössbauer studies of LixFeV3O8 (0≤x≤2)

We have used the 57Fe Mössbauer effect to study the electronic spin configuration of Fe in LixFeV3O8 (0≤x≤2) as a function of x. The Mössbauer effect results show that the Fe is localized and in the Fe3+ high spin state for all x. At 4.2K the isomer shift increases from 0.55 mm/s for x = 0 no Li to 0.60 mm/s as the lithium content increases to x = 2, fully lithiated. The hyperfine field increases from 395 k0e for x = 0 to 468 k0e for x = 2 and reflects the change in the electronic structure of the host from V5+(3d0) and V4+(3d1) to V4+(3d1) and V3+(3d2) and an increase in ionicity as the lithium content increases.

Alkaloids as ligands. 2. Synthesis and characterization of iron(II) halide complexes containing l-sparteine

Iron(II) compounds of l-sparteine, sp, are four-coordinate, pseudotetrahedral complexes of the type Fe(sp)X 2, where X is Cl, Br, or I. The infrared spectra suggest that sp adopts an all-chair conformation in these complexes. Furthermore, the infrared spectra show four bands below 600 cm −1, two of which are halide sensitive. These absorptions have been assigned to iron-ligand stretching modes. X-ray powder patterns of Fe(sp)Cl 2 and Fe(sp)Br 2 are identical to the analogous pseudotetrahedral cobalt(II) compounds. These iron compounds have room temperature magnetic moments close to 5.3 μ B and display a characteristics low-intensity absorption near 4000 cm −1 which has been assigned to the 5E → 5T 2 ligand-field transition. Mössbauer effect spectral results indicate the quadrupole interaction is approximately 2.9 mm/s. The chemical isomer shift increases from 1.03 to0 1.25 to 1.29 mm/s (relative to α-iron foil) for the chloride, bromide, and iodide complexes respectively. The latter two values are among the highest observed for tetrahedral iron(II) complexes.

Studies in Mössbauer spectroscopy. Part 11. Antimony-121 spectra of some complexes of palladium(II) and platinum(II) with tertiary stibines

Antimony-121 Mössbauer spectra have been obtained for 23 complexes of the type [MX2L2][L = SbPh3, Sb(C6H4Me-p)3, Sb(C6H4Me-o)3, SbEt3, or Sb(C6H11)3; M = Pd or Pt; X = Cl, I, or NO2], for the five-co-ordinate [Ptl2L3](L = SbMePh2 or SbMe2Ph), for [RhCl3(SbPh3)3], and for the free triarylstibines. In each case co-ordination results in a large increase in isomer shift and a decrease in quadrupole coupling constant, as expected for substantial removal of electron density from the lone pair on the antimony atom. In conjunction with far-i.r. data, configurations are assigned to the square-planar complexes, which are cis unless the stibine is sterically demanding. The cis and trans influences of the halides on the electron density on the antimony atom are shown to be opposed.

Electronic configuration of samarium sulphide and related compounds: Mössbauer-effect measurements and a model

$^{149}\mathrm{Sm}$ M\"ossbauer spectra have been measured at room temperature for SmS under applied pressures $P=0\ensuremath{-}11$ kbar and for ${\mathrm{Sm}}_{1\ensuremath{-}x}{\mathrm{Y}}_{x}\mathrm{S}$, $0\ensuremath{\le}x\ensuremath{\le}0.34$. There is a sharp increase in isomer shift at $P=6$ kbar and $x=0.15$, respectively, accompanying the transformation from the black to the gold phase, but there is no corresponding increase in linewidth. The samarium configuration, assumed to be a mixture of $4{f}^{6}$ and $4{f}^{5}5{d}^{1}$, is deduced as a function of $P$ or $x$. The results suggest that the $5d$ electron in the intermediate valence configuration is rather localized, but they are insensitive to whether the lattice is rigid or relaxed. Any fluctuations between the two configurations are more rapid than ${10}^{\ensuremath{-}9}$ sec. Caculations have been made with a Falicov Hamiltonian in which a term for $4f\ensuremath{-}5d$ hybridization is included. The model accounts for the observed variations of the samarium electron configuration. It is demonstrated, both theoretically and experimentally, that yttrium doping is not simply equivalent to pressure.

Electronic configuration mixing in Sm 1− xY xS

149Sm Mössbauer experiments have been performed at room temperature for different yttrium doped SmS samples. The discontinuous jconcentration-dependent electronic phase transition is accompanied by a sharp increase in isomer shift while the linewidth remains unchanged. The samarium configuration considered as a mixture of 4f 6 and 4f 5 5d 1 configurations, is derived as a function of yttrium concentration. Results are analysed in terms of the delocalization character of the 5d electrons. The electronic transition is accounted for by a Falicov type model including the hybridization between the localized 4f states and extended 5d states. The configurations deduced from the model are in good agreement with experimental results.

Metallkomplexe mit anionischen Liganden von Elementen der 4. Hauptgruppe, X Diskussion der Bindungsverhältnisse in Trihalogenstannidometallat(O)-Komplexen anhand der Ergebnisse von 119mSn-Mößbauer-Untersuchungen / Metal Complexes with Anionic Ligands of Elements of the Main Group IV, X 119mSn-Mössbauer-Spectroscopic Investigations and Bonding Properties of Trihalogenostannido Metalate(0) Complexes

The 119mSn and 57Fe Mößbauer spectra of the complexes [M(CO)6-n(SnX3)2]n- (n = 1,2,3,6) and [Fe(CO)4SnX3]- are reported. With increasing substitution of CO by [SnX3]-the isomer shift increases, reflecting also the π-acceptor strength of [SnX3]-. The π-back-bonding ability especially of [SnCl3]⁻ is similar to PCl3. A direct relationship between the isomer shift and the electronegativity of the halogen atoms of [SnX3]- and an inverse correlation between δ and Δ is observed.

Mössbauer Studies of Iron Organometallic Complexes. I. Iron Tetracarbonyl Complexes

Mössbauer absorption spectra at 78°K have been obtained for a series of compounds of the form R:Fe(CO)4, where R includes triphenylphosphine, triethylphosphite, acenaphthalene, trans-cinnamaldehyde, maleic anhydride, syn-syn-1,3-dimethyl-π-allyl cation, syn-1-methyl-π-allyl cation, π-allyl cation, and I2. The isomer shift increases and the electric quadrupole splitting decreases regularly through this series. The effect is explained in terms of the extent of forward coordination of the ligands, and so forms a basis for measuring Lewis basicity of ligands. The compound I2:Fe(CO)4 unexpectedly follows the trend, suggesting there remains appreciable bonding between iodine atoms.