Spin polarization of Co-Fe alloys estimated by point contact Andreev reflection and tunneling magnetoresistance

The compositional dependence on spin polarization of Co(100-x)Fe(x) alloys has been studied by point contact Andreev reflection (PCAR) and tunneling magnetoresistance (TMR) measurements. The intrinsic spin polarization for bcc Co(75)Fe(25) alloy is P = 0.58 + 0.03 at 4.2 K contrary to the pure Fe (P = 0.46 + 0.03) and Co (P = 0.45 + 0.03). The tunneling spin polarization values of Co(75)Fe(25) (110) textured polycrystalline electrode and (001) epitaxially grown electrode was estimated to be P(T) = 0.5 + 0.01 and P(T) = 0.57 + 0.01 at 8 K from the TMR ratios using Julliere's model for the MTJs prepared on oxidized Si and MgO (001) substrates. The spin polarization obtained from the tunneling junctions and PCAR experiments have been discussed. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3058699]