0000000000260912
AUTHOR
C. Herbort
Epitaxy of thin films of the Heusler compound Co2Cr0.6Fe0.4Al
Epitaxial thin films of the highly spin polarized Heusler compound Co2Cr0.6Fe0.4Al are deposited by dc magnetron sputtering. It is shown by XRD and TEM investigations how the use of an Fe buffer layer on MgO(100) substrates supports the growth of highly ordered Co2Cr0.6Fe0.4Al at low deposition temperatures. The as grown samples show a relatively large ordered magnetic moment of mu = 3.0mu_B/f.u. providing evidence for a low level of disorder.
Epitaxy of thin films of the Heusler compound
Abstract Epitaxial thin films of the highly spin polarized Heusler compound Co 2 Cr 0.6 Fe 0.4 Al are deposited by DC magnetron sputtering. It is shown by XRD and TEM investigations how the use of an Fe buffer layer on MgO(1 0 0) substrates supports the growth of highly ordered Co 2 Cr 0.6 Fe 0.4 Al at low deposition temperatures. The as-grown samples show a relatively large ordered magnetic moment of μ ≃ 3.0 μ B / f . u . providing evidence for a low level of disorder.
Electronic properties of *-oriented thin films
Abstract To perform high precision measurements of the transport anisotropy, epitaxial, a *-oriented thin films of UPd 2 Al 3 have been prepared on LaAlO 3 (1 1 0) substrates. The critical temperature T c ≈ 1.75 K and the upper critical field B c 2 ≈ 3 T are comparable to typical bulk values. In contrast to UNi 2 Al 3 , we observed only a weak anisotropy in directional resistivity measurements, especially no dependence of the superconducting transition temperature on the direction of the applied current. Hall effect measurements show two characteristic minima at T = 16 K ≈ T N and T ≈ 6 K , which corresponds to features seen in earlier measurements on c *-oriented films.
Brillouin light scattering study of Co$_{2}$Cr$_{0.6}$Fe$_{0.4}$Al and Co$_{2}$FeAl Heusler compounds
The thermal magnonic spectra of Co$_{2}$Cr$_{0.6}$Fe$_{0.4}$Al (CCFA) and Co$_2$FeAl were investigated using Brillouin light scattering spectroscopy (BLS). For CCFA, the exchange constant A (exchange stiffness D) is found to be 0.48 $\mu$erg/cm (203 meV A$^2$), while for Co$_2$FeAl the corresponding values of 1.55 $\mu$erg/cm (370 meV A$^2$) were found. The observed asymmetry in the BLS spectra between the Stokes and anti-Stokes frequencies was assigned to an interplay between the asymmetrical profiles of hybridized Damon-Esbach and perpendicular standing spin-wave modes, combined with the optical sensitivity of the BLS signal to the upper side of the CCFA or Co$_2$FeAl film.
Magnetism of Co-doped ZnO thin films
We have investigated magnetic and transport properties of 5% Co-doped and undoped ZnO thin films deposited on $r$ plane ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ substrates by pulsed laser deposition. The Co doped films showed paramagnetic and ferromagnetic behavior as well as a high magnetoresistance and a small anomalous Hall effect. In a range of $0\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ at low temperatures we observed a double sign change of the magnetoresistance. For undoped ZnO films, prepared by the same conditions, only a negative MR was observed, but surprisingly also a very small anomalous Hall effect. We explain our results…
Effects of post-growth annealing on structural and compositional properties of the Co2Cr0.6Fe0.4Al surface and its relevance for the surface electron spin polarization
In this study we investigate the influence of post-growth annealing on different Co2Cr0.6Fe0.4Al samples. We find strong changes in the geometric surface structure as well as in the element specific concentrations during the annealing process. These irreversible changes go in hand with characteristic changes in the electron spin polarization (ESP) at the surface: as observed in Cinchetti et al (2007 J. Phys. D: Appl. Phys. 40 1544), the iron buffered sample shows the largest spin polarization at the Fermi level. The latter remains positive as a consequence of the reduced density of states for the minority carriers due to the predicted minority gap, which can be clearly seen for all samples …
Morphology and magnetoresistance of Co2Cr0.6Fe0.4Al-based tunnelling junctions
Some ferromagnetic Heusler compounds are theoretically predicted to be half metallic materials, i.e. to be characterized by a huge spin polarization at the Fermi energy. We investigate the correlations between junction preparation conditions, morphology and transport properties of planar MgO/Co2Cr0.6Fe0.4Al/AlOx/Co/CoOx/Pt tunnelling junctions. Epitaxial Co2Cr0.6Fe0.4Al thin films were deposited by dc and rf magnetron sputtering on different buffer layers (Cr, Fe, MgO) on MgO(1 0 0) substrates. By RHEED, LEED and in situ STM investigations different surface morphologies were observed. Atomically flat surfaces with Co2Cr0.6Fe0.4Al unit cell sized steps (B2 structure) were obtained by rf sput…
Spin-resolved unoccupied density of states in epitaxial Heusler-alloy films
We investigate the electronic properties of epitaxial ${\text{Co}}_{2}({\text{Fe}}_{x}{\text{Mn}}_{1\ensuremath{-}x})\text{Si}$, ${\text{Co}}_{2}\text{Fe}({\text{Al}}_{1\ensuremath{-}x}{\text{Si}}_{x})$, and ${\text{Co}}_{2}({\text{Cr}}_{0.6}{\text{Fe}}_{0.4})\text{Al}$ films on MgO(100) substrates using circular dichroism in x-ray absorption spectroscopy (XMCD). Considering final-state electron correlations, the spin-resolved partial density of states at the Co atom can be extracted from XMCD data. The experimental results corroborate the predicted half-metallic ferromagnetic properties of these alloys and reveal a compositional dependence of the Fermi energy position within the minority b…