37 research outputs found
Preparation and structural properties of thin films and multilayers of the Heusler compounds Cu2MnAl, Co2MnSn, Co2MnSi and Co2MnGe
We report on the preparation of thin films and multilayers of the
intermetallic Heusler compound CuMnAl, Co2MnSn, Co2MnSi and Co2MnGe by
rf-sputtering on MgO and Al2O3 substrates. Cu2MnAl can be grown epitaxially
with (100)-orientation on MgO (100) and in (110)-orientation on Al2O3 a-plane.
The Co based Heusler alloys need metallic seedlayers to induce high quality
textured growth. We also have prepared multilayers with smooth interfaces by
combining the Heusler compounds with Au and V. An analysis of the ferromagnetic
saturation magnetization of the films indicates that the Cu2MnAl-compound tends
to grow in the disordered B2-type structure whereas the Co-based Heusler alloy
thin films grow in the ordered L21 structure. All multilayers with thin layers
of the Heusler compounds exhibit a definitely reduced ferromagnetic
magnetization indicating substantial disorder and intermixing at the
interfaces.Comment: 21 pages, 8 figure
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 . While the substitution of the transition metal
atoms may preserve the half-ferromagnetic character, substituting the 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
Half-metallicity and Slater-Pauling behavior in the ferromagnetic Heusler alloys
Introductory chapter for the book "Halfmetallic Alloys - Fundamentals and
Applications" to be published in the series Springer Lecture Notes on Physics,
P. H. Dederichs and I. Galanakis (eds). It contains a review of the theoretical
work on the half-metallic Heusler alloys.Comment: Introductory chapter for the book "Halfmetallic Alloys - Fundamentals
and Applications" to be published in the series Springer Lecture Notes on
Physics, P. H. Dederichs and I. Galanakis (eds
Electrical, morphological and structural properties of RF magnetron sputtered Mo thin films for application in thin film photovoltaic solar cells
Molybdenum (Mo) thin films were deposited using radio frequency magnetron sputtering, for application as a metal back contact material in ‘‘substrate configuration’’ thin film solar cells. The variations of the electrical, morphological, and structural properties of the deposited films with sputtering pressure, sputtering power and post-deposition annealing were determined. The electrical conductivity of the Mo films was found to increase with decreasing sputtering pressure and increasing sputtering power. X-ray diffraction data showed that all the films had a (110) preferred orientation that became less pronounced at higher sputtering power while being relatively insensitive to process pressure. The lattice stress within the films changed from tensile to compressive with increasing sputtering power and the tensile stress increased with increasing sputtering pressure. The surface morphology of the films changed from pyramids to cigar-shaped grains for a sputtering power between 100 and 200 W, remaining largely unchanged at higher power. These grains were also observed to decrease in size with increasing sputtering pressure. Annealing the films was found to affect the resistivity and stress of the films. The resistivity increased due to the presence of residual oxygen and the stress changed from tensile to compressive. The annealing step was not found to affect the crystallisation and grain growth of the Mo films