MxTiSe2 (M = Cr, Mn, Cu) electronic structure study by methods of resonant X-ray photoemission spectroscopy and X-Ray absorption spectroscopy

Electronic structure and chemical bonding in TiX2 (X=S, Se, Te), TMxTiSe2 (TM=Cr, Mn, Cu) and CrxTi1-xSe2 were studied by x-ray resonance photoemission and absorption spectroscopy. These methods are detected to be strong sensitive to chemical bonding. Charge transfer from the intercalated atoms to Ti 3d band is detected. Narrow Ti 3d and Cu 3d bands are observed under Fermi level in CuxTiSe2.Comment: 7 pages, 4 figeres, ISIC 16 conferenc

Magnetic circular dichroism in X-ray fluorescence of Heusler alloys at threshold excitation

The results of fluorescence measurements of magnetic circular dichroism (MCD) in Mn L_2,L_3 X-ray emission and absorption for Heusler alloys NiMnSb and Co2MnSb are presented. Very intense resonance Mn L_3 emission is found at the Mn 2p_3/2 threshold and is attributed to a peculiarity of the threshold excitation in materials with the half-metallic character of the electronic structure. A theoretical model for the description of resonance scattering of polarized x-rays is suggested.Comment: 3 pages, 2 figures. Discussed at conferences, submitting process in progres

Origin and Properties of the Gap in the Half-Ferromagnetic Heusler Alloys

We study the origin of the gap and the role of chemical composition in the half-ferromagnetic Heusler alloys using the full-potential screened KKR method. In the paramagnetic phase the C1_b compounds, like NiMnSb, present a gap. Systems with 18 valence electrons, Z_t, per unit cell, like CoTiSb, are semiconductors, but when Z_t > 18 antibonding states are also populated, thus the paramagnetic phase becomes unstable and the half-ferromagnetic one is stabilized. The minority occupied bands accommodate a total of nine electrons and the total magnetic moment per unit cell in mu_B is just the difference between Z_t and $2 \times 9$. While the substitution of the transition metal atoms may preserve the half-ferromagnetic character, substituting the $sp$ atom results in a practically rigid shift of the bands and the loss of half-metallicity. Finally we show that expanding or contracting the lattice parameter by 2% preserves the minority-spin gap.Comment: 11 pages, 7 figures New figures, revised tex

Nonquasiparticle states in half-metallic ferromagnets

Anomalous magnetic and electronic properties of the half-metallic ferromagnets (HMF) have been discussed. The general conception of the HMF electronic structure which take into account the most important correlation effects from electron-magnon interactions, in particular, the spin-polaron effects, is presented. Special attention is paid to the so called non-quasiparticle (NQP) or incoherent states which are present in the gap near the Fermi level and can give considerable contributions to thermodynamic and transport properties. Prospects of experimental observation of the NQP states in core-level spectroscopy is discussed. Special features of transport properties of the HMF which are connected with the absence of one-magnon spin-flip scattering processes are investigated. The temperature and magnetic field dependences of resistivity in various regimes are calculated. It is shown that the NQP states can give a dominate contribution to the temperature dependence of the impurity-induced resistivity and in the tunnel junction conductivity. First principle calculations of the NQP-states for the prototype half-metallic material NiMnSb within the local-density approximation plus dynamical mean field theory (LDA+DMFT) are presented.Comment: 27 pages, 9 figures, Proceedings of Berlin/Wandlitz workshop 2004; Local-Moment Ferromagnets. Unique Properties for Moder Applications, ed. M. Donath, W.Nolting, Springer, Berlin, 200

Electron correlation effects in band structure of magnetic clusters Mn-12 and Fe-8

Contains fulltext : 60381.pdf (publisher's version ) (Closed access)We present calculations of electronic structure and local magnetic moment of 3d metals in [Mn12O12(CH3COO)(16)(H2O)(24)].2CH(3)COOH.4H(2)O and I(C6H15N3)(6)Fe8O2(OH)(12)]Br-7(H2O)Br.8H2O, abbreviated Mn-12 and Fe8Br8, respectively. The comparison of calculated and experimental soft X-ray spectra shows that p-d mixing is very sensitive to the value of the local Coulomb repulsion parameter U. This result is found to be in agreement with experimental resonant inelastic X-ray scattering spectra (RIXS) and X-ray photoelectron spectra (XPS), which have been used to study electron correlation effects in magnetic clusters. The O 2p-Me 3d separation found in the experiment, is well reproduced by LDA + U band structure calculations, which include on-site Coulomb interactions. The 3d metal L-2,L-3 RIXS behaviour reflects the presence of the local magnetic moment and confirms the existence of the energy gap in the 3d band of the metal. (C) 2004 Elsevier B.V. All rights reserved

Ion irradiation induced reduction of Fe3+^{3+} to Fe2+^{2+} and Fe0^0 in triethoxysilane films

Silica gel films prepared from mixtures of triethoxysilane (TH) and Fe nitrate Fe(NO)3·9H2O were irradiated with various fluences of 3 MeV Au ions. Silicon 2p x-ray absorption (XAS) and L2,3 x-ray emission spectra of irradiated TH:Fe films are found to be very similar to those of SiO2, providing direct evidence of the formation of a glassy matrix. Fe L2,3 XAS shows the reduction of Fe3+ ions at low fluence, initially attributed to the formation of Fe metallic nanoparticles. Mössbauer spectra of films irradiated with higher ion fluences are well fitted by a singlet associated with superparamagnetic Fe particles and a doublet associated with Fe2+ ions in Fe–Si–O complexes