Spin polarization and Gilbert damping of Co2Fe(GaxGe1−x) Heusler alloys

Abstract The spin polarization ( P ) of ferromagnetic Heusler alloys, Co 2 Fe(Ga x Ge 1− x ) ( x = 0, 0.25, 0.5, 0.75, and 1), is investigated by point contact Andreev reflection (PCAR) measurements. While the P values of the ternary Co 2 FeGe and Co 2 FeGa alloys are 0.58 and 0.59, respectively, the corresponding value for Co 2 Fe(Ge 0.5 Ga 0.25 ) is as high as 0.69. Co 2 Fe(Ge 0.5 Ga 0.5 ) alloy shows a strong tendency for L2 1 ordering and a high Curie temperature of 807 °C. Ab initio calculations indicate that the band structures of the Co 2 FeGe and Co 2 Fe(Ge 0.5 Ga 0.5 ) alloys with L2 1 or B2 structures are half-metallic. Thin films of the quaternary Co 2 Fe(Ge 0.5 Ga 0.5 ) alloy grown on MgO(0 0 1) substrates order to the L2 1 structure upon annealing at 500 °C, giving rise to a high P of 0.75. This is the highest P value reported for Heusler alloy thin films using the PCAR technique. Ferromagnetic resonance measurements show that the Gilbert damping constant of the film is ∼0.008. All these indicate that the Co 2 Fe(Ge 0.5 Ga 0.5 ) alloy is promising as a spin polarized current source for spintronics devices.