ON THE PHOTOFRAGMENTATION OF FE(CO)5 .1. INFRARED AND MOSSBAUER EVIDENCE FOR THE FORMATION OF FE(CO)4 IN POLYMER MATRICES

80273073

Quasiparticle dynamics in ferromagnetic compounds of the Co-Fe and Ni-Fe systems

We report a theoretical study of the quasiparticle lifetime and the quasiparticle mean free path caused by inelastic electron-electron scattering in ferromagnetic compounds of the Co-Fe and Ni-Fe systems. The study is based on spin-polarized calculations, which are performed within the $GW$ approximation for equiatomic and Co- and Ni-rich compounds, as well as for their constituents. We mainly focus on the spin asymmetry of the quasiparticle properties, which leads to the spin-filtering effect experimentally observed in spin-dependent transport of hot electrons and holes in the systems under study. By comparing with available experimental data on the attenuation length, we estimate the contribution of the inelastic mean free path to the latter.Comment: 10 pages, 10 figure

ELECTRONIC STRUCTURE AND MÖSSBAUER HYPERFINE INTERACTIONS IN RUTHENIUM COMPLEXES

Des calculs d'orbitales moléculaires par la méthode SCCC-MO (auto-consistante en charge et configuration) ont éte effectués avec six ions complexes de Ruthénium ; Ru(CN)4-6, Ru(NH3)2+6, Ru(NH3)3+6, Ru(CN)5NO2-, RuCl5NO2-, et Ru(NH3)5NO3+, dans le but d'étudier les effets de covalence dans les interactions hyperfines du Ruthénium. Les paramètres empiriques indispensables à la méthode SCCC-MO ont été choisis par l'ajustement des transitions électroniques calculées à partir de celles mesurées par spectroscopie optique des complexes en solution. Les populations électroniques ainsi obtenues ont été utilisées dans l'interprétation des déplacements isomériques Mössbauer (IS) et des interactions quadrupolaires (ΔEQ). Le tableau I reproduit les valeurs mesurées de IS avec les complexes de Ru. Ces valeurs sont comparées aux populations 5s et 4d du Ru, obtenues d'après les calculs d'orbitales moleculaires. On observe que la valeur de IS augmente avec la population 5s et avec la déroissance de la population 4d. Les ligands contenant des orbitales =-antiliantes de basse énergie conduisent à des populations 4d moins importantes. Le tableau II donne les valeurs de l'interaction quadrupolaire mesurée et calculée. Ces dernières ont été obtenues de l'expression : ΔEQ = 1/2 e2 Q 3/2 4/7 4d (ηdxy- ηdxz,yz)(1 - R) avec les valeurs Q3/2 (99Ru) = 0,29 barn, 4d = 5,19 a-30, (1 - R) = 0,68 ; ηdxy et ηdxz,yz représentent les populations obtenues des calculs MO. Ces calculs indiquent ΔEQ > 0 dans les trois complexes de ruthénium. ΔEQ a été aussi calculé pour Fe(CN)5NO2- en utilisant des résultats de calcul MO publiés et les valeurs Q3/2 (57Fe) = 0,2 barn, = 4,93 a-30. L'accord satisfaisant trouvé entre les valeurs experimentales et calculées de ΔEQ sont à l'appui de l'hypothèse selon laquelle les distortions des couches d, dues à la délocalisation des électrons vers les liantes, contribuent d'une façon majeure à la valeur du gradient de champ électrique.Molecular orbital calculations with the SCCC-MO method (self consistent charge and configuration) were performed for six Ruthenium complex ions, namely | Ru(CN)6 |-4, | Ru(NH3) 6 | +2, | Ru(NH3) 6 |+3, | Ru(CN)5NO |-2, | RuCl5NO |-2 and | Ru(NH3)5NO |+3, in order to study covalency effects in the Mossbauer hyperfine interactions of Ruthenium. Empirical parameters required in the calculations with the SCCC-MO method were chosen by approximately fitting calculated electronic transitions to those measured experimentally by optical spectroscopy of the complexes in solution. The electron populations obtained were then used to interpret Mössbauer isomer shifts (I.S.) and quadrupole splittings (ƊEQ). Table I reproduces the values of measured I. S. for the Ru complexes. These values are compared to the 5s and 4p populations of Ru, obtained with the M. O. calculations. It is seen that the I. S. value is increased both by increase of the 5s population and by decrease of the 4d population. Ligands containing low-energy π-antibonding orbitals to which back-donation can take place produce lower 4d populations. Table II shows measured and calculated quadrupole splitting values (ΔEQ) for Ru complexes ; calculated values are given by : ΔEQ = 1/2 e2 Q3/2 4/7 4d (ndxy - ndxz,yz) (1 - R) in which were used the values Q3/2(99Ru) = 0.29 barn, 4d = 5.19 a-30, (1 - R) = 0.68 : ndxy and ndxz,yz are 4d populations obtained with the M. O. calculations. These calculations predict ΔEQ > 0 in all three Ru complexes. ΔEQ value was also calculated for | Fe(CN)5NO |-2, using published M. O. results 2 and the values Q3/2(57Fe) = 0.2 barn, 3d = 4.93 a-30. The satisfactory agreement found between experimental and calculated ΔEQ values support the assumption that distortions of d shells due to back-donation provide the major contribution to the electric field gradient

On The Photofragmentation Of Fe(co)5. Ii. Molecular Orbital Studies Of Fe(co)n, 1≥n≥5

Self-consistent molecular orbital calculations were performed for Fe(CO)5 and its photofragments Fe(CO)n, 1≤n<5. The discrete variational method was employed, with the Xα local approximation for the exchange interaction. In the case of Fe(CO)5, photoelectron and optical spectra are analyzed, and photochemical behavior is discussed. The Mössbauer isomer shifts and quadrupole splittings are investigated. In the case of Fe(CO)5 and Fe(CO)4, the values derived for these hyperfine interactions are compared to experimental measurements reported in a polyethylene matrix. © 1984 American Institute of Physics.80273574

Symmetry-dependent Mn-magnetism in Al 69.8 Pd 12.1 Mn 18.1

We investigated the stability of magnetic moments in Al 69.8 Pd 12.1 Mn 18. 1 . This alloy exists in both, the icosahedral (i) and the decagonal (d) quasicrystalline form. The transition from the i- to the d-phase is achieved by a simple heat treatment. We present the results of measurements of the 27 Al NMR-response, the dc magnetic susceptibility, and the low-temperature specific heat of both phases. In the icosahedral compound, the majority of the Mn ions carries a magnetic moment. Their number is reduced by approximately a factor of two by transforming the alloy to its decagonal variety. For both compounds, we have indications for two different local environments of the Al nuclei. The first reflects a low density of states of conduction electrons and a weak coupling of the Al nuclei to the Mn-moments. The second type of environment implies a large d-electron density of states at the Fermi level and a strong coupling to the magnetic Mn moments. Spin-glass freezing transitions are observed at T deca f =12 K for the decagonal, and T ico f =19 K for the icosahedral phase. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005