Enhanced tunneling spin polarization from ultrathin layers of amorphous CoFe

The tunneling spin polarization of CoFe alloys is directly compared in their amorphous (<∼25-30 Å) and crystalline states using superconducting tunneling spectroscopy measurements of Al95Si 5/Al2O3/CoFe junctions. Ultrathin layers of normally crystalline CoFe are made amorphous by sandwiching them between amorphous alumina tunnel barriers and amorphous ferromagnetic CoFeB electrodes. The results show that the tunneling spin polarization is significantly enhanced when the CoFe alloy is made amorphous compared to when it is crystalline. We also show that a postdeposition atomic oxygen treatment of the alumina tunnel barrier significantly enhances the thermal stability of the junctions. © 2009 American Institute of Physics.