A. Szajek

The electronic and magnetic properties of Yn+1Co3n+5B2n (n = 0, 1, 2, 3, and ∞) systems

Abstract The compounds of the R n +1 Co 3 n +B 2 n family crystallize in a hexagonal structure having the P6/mmm space group. They were generally studied in connection with their possible use as permanent magnets. The ab initio spin-polarized TB LMTO-ASA band structure calculations have been performed for the following five representative of the family: YCo 5 , YCo 4 B, Y 3 Co 11 B 4 , Y 2 Co 7 B 3 and YCo 3 B 2 . The cobalt atoms occupying distinct sites have different types and numbers of neighbouring atoms and as a consequence the magnetic moments are different. The calculated values are compared with the bulk measurements.

The electronic and electrochemical properties of the LaNi5, LaNi4Al and LaNi3AlCo systems

Abstract Nanocrystalline LaNi 5 -type materials have been prepared by mechanical alloying (MA) followed by annealing. The amorphous phase forms directly from the starting mixture of elements, without formation of other phases. The LaNi 5 , LaNi 4 Al and LaNi 3 AlCo systems crystallize in the hexagonal CaCu 5 type structure ( P6/mmm ). The electrochemical properties of these type of materials, in which there has been a partial substitution of Ni by Al and Al–Co, have been investigated and discharge capacity enhancement has been observed. The electronic structure has been studied by the tight binding version of the linear muffin-tin orbital method in the atomic sphere approximation (TB-LMTO ASA). Total energy calculations showed that the Al and Co impurities prefer 3g positions.

X-ray photoemission spectra of La0.7Sr0.3MnO3 perovskite

Abstract X-ray photoemission (XPS) measurements of the core levels and valence electronic structure of La0.7Sr0.3MnO3 are presented. The ferromagnetic phase La0.7Sr0.3MnO3 is half-metallic, which is important in the relation to colossal magnetoresistance properties of this compound. Comparing XPS measurements, and the LMTO band-structure calculations for La0.75Sr0.25MnO3, one concludes that the electronic structure of La0.7Sr0.3MnO3 compound consists mainly Mn 3d and O 2p states. In addition, the Mn 3d and O 2p states are hybridized over whole valence band. States of 3d character localized in Mn site predominate near the top of the valence band.

The influence of partial substitution of Co by Al atoms on the magnetic properties of DyCo2 compound

Abstract New results of experimental investigations of the physical properties of Dy(Co 1− x Al x ) 2 compounds, where x = 0.0, 0.1 and 0.2, are presented. These systems crystallize in the whole range of the concentration x in the Laves-phase MgCu 2 crystal structure. The zero field cooled (ZFC) and field cooled (FC) magnetization measurements were performed on the pseudobinary Dy(Co 1− x Al x ) 2 cubic compounds. The composition dependence of the Curie temperature is discussed on the basis of electronic structure calculations.

Electronic structure of superconducting non-oxide perovskite MgCNi3

The recently discovered superconductor MgCNi3 crystallizes in the classical cubic perovskite structure. The electronic structures of the MgCNi3-xMx (M = Co, Cu; x = 0, 0.5, 1.0) system have been calculated using the self-consistent tight-binding linear muffin-tin orbital method. The calculations showed that the Fermi level for MgCNi3 is located in the slope descending from a sharp peak originating from d states of Ni atoms. Electron (Cu) and hole (Co) doping of MgCNi3 reconstructs its band structure but does not lead to magnetic order.

Magnetic properties and electronic structures of intermediate valence systems CeRhSi2 and Ce2Rh3Si5

The crystal structures and the physical (magnetic, electrical transport and thermodynamic) properties of the ternary compounds CeRhSi(2) and Ce(2)Rh(3)Si(5) (orthorhombic CeNiSi(2)- and U(2)Co(3)Si(5)-type structures, respectively) were studied over wide ranges of temperature and magnetic field strength. The results revealed that both materials are valence fluctuating systems, in line with previous literature reports. Direct evidence for valence fluctuations was obtained by means of Ce L(III)-edge x-ray absorption spectroscopy and Ce 3d core-level x-ray photoelectron spectroscopy. The experimental data were confronted with the results of ab initio calculations of the electronic band structures in both compounds.

Spin wave spectrum and magnetization of ferromagnetic modulated films

Abstract A system of localized spins interacting by periodically modulated exchange interaction is considered. The spin wave spectrum is determined by solving numerically equations of motion for the magnon Green function. The magnon densities of states projected on the direction of modulation and the total 3-d one are calculated. Results are applied to calculate the low temperature dependence of magnetization. The Bloch law of magnetization is obeyed by the model with coefficients weakly depending on the modulation wave vector.

X-ray photoemission spectra and electronic structure of GdCo4B

Abstract New results on the electronic properties of GdCo 4 B are reported. This compound crystallizes in the hexagonal CeCo 4 B type structure. The electronic structure has been studied by X-ray photoemission spectroscopy (XPS). The valence band (VB) of the X-ray photoemission spectra is determined mainly by the Co(3d) and Gd(4f) bands. The VB spectrum is compared with ab initio electronic structure calculations performed with the linearized muffin-tin orbital (LMTO) method. The calculated magnetic moment of 3.276 μ B /f.u. is in good agreement with the experimental value, 2.96 μ B /f.u., of the saturation magnetization.

Electronic structure of La0.65Pb0.35MnO3 perovskite studied by X-ray photoemission spectroscopy

Abstract The electronic structure of La 0.65 Pb 0.35 MnO 3 has been studied by X-ray photoemission spectroscopy (XPS). The valence band spectrum is compared with ab-initio electronic structure calculations using linearized muffin–tin orbital (LMTO) method. The XPS measurements, and the theoretical band-structure calculations for La 0.75 Pb 0.25 MnO 3 , show that the electronic structure of La 0.65 Pb 0.35 MnO 3 compound consists mainly of Mn 3d and O 2p states. In addition, the Mn 3d and O 2p states are hybridized over the whole valence band. States of 3d characters localized in Mn site predominate near the top of the valence band. We have found a good agreement between the experimental valence band spectra and theoretical calculations.

Electronic structure of doped LaMnO3 perovskite studied by x-ray photoemission spectroscopy

The electronic structure of La2/3Sr1/6Pb1/6MnO3 has been studied by x-ray photoemission spectroscopy (XPS). The valence band spectrum is compared with ab initio electronic structure calculations using a linearized muffin-tin orbital (LMTO) method. The XPS measurements and the theoretical band structure calculations for La1/2Sr1/4Pb1/4MnO3 show that the electronic structure consists mainly of Mn(3d) and O(2p) states. In addition, the Mn(3d) and O(2p) states are hybridized over the whole valence band. States of 3d character localized on Mn sites predominate near the top of the valence band. It was found that the doping, both with the Pb and the Sr ions, increases the spin polarization by up to 48%.