Electronic structure and spectroscopy of the quaternary Heusler alloy Co₂Cr_1−xFe_xAl

Abstract

Quaternary Heusler alloys Co2Cr1−xFexAl with varying Cr to Fe ratio x were investigated experimentally and theoretically. The electronic structure and spectroscopic properties were calculated using the full relativistic Korringa–Kohn–Rostocker method with coherent potential approximation to account for the random distribution of Cr and Fe atoms as well as random disorder. Magnetic effects are included using spin dependent potentials in the local spin density approximation.Magnetic circular dichroism in x-ray absorption was measured at the L2,3 edges of Co, Fe and Cr of the pure compounds and the x = 0.4 alloy in order to determine element specific magnetic moments. Calculations and measurements show an increase of the magnetic moments with increasing iron content. Resonant (560–800 eV) soft x-ray as well as high resolution–high energy (⩾3.5 keV) hard x-ray photo emission was used to probe the density of the occupied states in Co2Cr0.6Fe0.4Al.

Local formation of a Heusler structure in CoFe–Al alloys

“…Co 2 FeAl in the B2 type structure is predicted to conserve the high spin polarization [14][15][16] assumed for Co 2 FeAl in the L2 1 type structure and consequently, the bulk spin-scattering asymmetry in the CPP-GMR spin-valves.…”

Spin-dependent tunneling characteristics of fully epitaxial magnetic tunneling junctions with a full-Heusler alloy Co2MnSi thin film and a MgO tunnel barrier

“…Due to the existence of an energy gap at the Fermi level ͑E F ͒ for one spin direction, half-metallic ferromagnets are characterized by a complete spin polarization at E F , 1 so these are the most promising ferromagnetic electrode materials for spintronic devices. Co-based full-Heusler alloys have been extensively studied recently as candidates for use in half-metallic ferromagnetic electrodes 2,3 and regarding their application to magnetic tunnel junctions ͑MTJs͒. [4][5][6][7][8][9][10][11][12][13] This is because of the half-metallic ferromagnetic nature theoretically predicted for some of these alloys 14,15 and because of their high Curie temperatures, which are well above room temperature ͑RT͒.…”

Spectroscopy of the electronic states of the Heusler compounds Co2FeAl and Co2Cr0.6Fe0.4Al and the influence of oxidation

“…However, they are close and it cannot be excluded that feature D is related to beginning sample oxidation. At these energies, no peaks in the bulk densities of states were calculated for both compounds [18,17,9,30], but, as we will show in section V, these peaks could be generated by direct transitions into a free electron-like parabolic band.…”

“…However, ARPES is extremely surface sensitive and the preparation of Heusler compounds with clean and well ordered surface for such measurements poses a major challenge. Valence band spectroscopy is usually performed on bulk samples which are fractured or polished inside the spectroscopy chamber (e. g. [9,10,11]). Another approach is a sequence of sputter cleaning and annealing processes of a bulk or thin film sample (often capped with a protection layer) after ex-situ transfer into an analysis chamber [12,13].…”