Spin polarization of magnetoresistive materials by point contact spectroscopy

Abstract

In the strive to find a straightforward method for determining the spin polarization, the analysis of the Andreev reflection process in point contact junctions has attracted much interest. However, the prerequisite for an evaluation of the transport spin polarization in this scheme is the existence of elastic (ballistic or diffusive) transport, which cannot be assumed a priori. We therefore also include inelastic processes in our analysis and exemplify that thermal effects can have a significant effect on data evaluation. As ferromagnetic samples with a predicted half metallic behavior and comparably low conductivity we used thin films of the double perovskite Sr2FeMoO6 and bulk material of the Heusler compound Co2Cr0.6Fe0.4Al

Electronic structure and spectroscopy of the quaternary Heusler alloy Co2Cr1−xFexAl

“…Very recently, Marukame et al [31] reported a TMR ratio of 74% at 55K for a Co 2 Cr 0.6 Fe 0.4 Al-MgO-CoFe magnetic tunnel junction. A spin polarisation of only less than 49% was found for polycrystalline samples by means of Andreev reflections [32]. The observation of an incomplete spin polarisation may not only be caused by the model used to interpret the data [32,33] but also by the properties of the sample.…”

Spintronics: Fundamentals and applications

“…Conversely, at a fixed exchange energy, an increase in Fermi velocity mismatch could increase the subgap conductance. 100 In a typical interpretation of a measured conductance, complications can then arise in trying to disentangle the influence of parameters Z, P G , and Fermi velocity mismatch from the nature of the point contacts (Kikuchi et al, 2002) and the role of inelastic scattering (Auth et al, 2003). Detection of P in a high-temperature superconductor is even possible with a large barrier or a vacuum between the F and S regions, as proposed by Wang and Hu (2002) using resonant Andreev reflection and a d-wave superconductor.…”

Epitaxial growth of Co2Cr0.6Fe0.4Al Heusler alloy thin films on MgO (0 0 1) substrates by magnetron

“…Cobalt-based full-Heusler alloys have been considered potential candidates for showing HMF properties. Their structural and magnetic properties have been intensively investigated experimentally [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] and theoretically [19][20][21][22][23] because they have comparatively high Curie temperatures T C . In particular, Co 2 Cr 1−x Fe x Al (CCFA) is expected to have suitable electro-magnetic properties for injecting a spinpolarized current [16,22].…”