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

The compositional dependence on spin polarization of Co100-x Fex alloys has been studied by point contact Andreev reflection (PCAR) and tunneling magnetoresistance (TMR) measurements. The intrinsic spin polarization for bcc Co75 Fe25 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 Co75 Fe25 (110) textured polycrystalline electrode and (001) epitaxially grown electrode was estimated to be PT =0.5±0.01 and PT =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.