Existence of a second A3 phase in B2 epitaxial Co2Cr1−xFexAl thin films

The Heusler alloy Co2Cr1−xFexAl, predicted to be half-metallic for low x, has recently shown relatively large giant and tunnel magnetoresistances in thin film structures. However, the saturation magnetic moment and spin polarization for low x films has been found to fall significantly short of the theoretical half-metallic values. Using transmission electron microscopy and X-ray diffraction, we have observed the presence of a second hcp A3 phase in B2 epitaxial thin films of Heusler alloy Co2Cr1−xFexAl with x<1. Assuming this second phase to have a lower magnetic moment and spin polarization than the B2 phase explains the reduction in magnetic moments and spin polarizations observed in this class of compounds.