Epitaxial Co2Cr0.6Fe0.4Al thin films and magnetic tunnelling junctions

Epitaxial thin films of the theoretically predicted half metal Co2Cr0.6Fe0.4Al were deposited by dc magnetron sputtering on different substrates and buffer layers. The samples were characterized by x-ray and electron beam diffraction (RHEED) demonstrating the B2 order of the Heusler compound with only a small fraction of disorder on the Co sites. Magnetic tunnelling junctions with Co2Cr0.6Fe0.4Al electrode, AlOx barrier and Co counter electrode were prepared. From the Jullière model a spin polarization of Co2Cr0.6Fe0.4Al of 54% at T = 4 K was deduced. The relation between the annealing temperature of the Heusler electrodes and the magnitude of the tunnelling magnetoresistance effect was investigated and the results are discussed in the framework of morphology and surface order based on in situ scanning tunnelling microscopy (STM) and RHEED investigations.