Structural, magnetic, and transport properties of full-Heusler alloy Co2(Cr1−xFex)Al thin films

Abstract

The structural, magnetic, and transport properties are investigated for full-Heusler alloy Co2(Cr1−xFex)Al (CCFA) thin films sputtered on thermally oxidized Si substrates at room temperature (RT). X-ray diffraction reveals that the films possess the B2 structure for x=0, decrease the atomic site ordering by substituting Fe for Cr(0.4≦x≦0.6), and form the A2 structure for x=1. Both the magnetic moment and the Curie temperature of the films increase with increasing Fe content (x), although the moment for x<1 is significantly smaller than that of the calculated value for the L21 structure. Magnetic tunnel junctions (MTJs) with CCFA films as either upper or bottom ferromagnetic layers are also fabricated by using metal masks. The maximum tunneling magnetoresistance (TMR) at RT for the MTJ was observed to be 19.1% for x=0.4 with the CCFA film as an upper ferromagnetic layer, despite the atomic disorder of the CCFA film. This is consistent with our previous TMR observation with the CCFA film as a bottom ferromagnetic layer, indicating that the CCFA film even with the B2 structure is a good candidate for future spintronic devices due to its disorder tolerance, high reproducibility, and large spin polarization.