Co-Based Heusler Alloys for CPP-GMR Spin-Valves With Large Magnetoresistive Outputs

We studied various Heusler alloy compositions for the ferromagnetic layers of current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) spin-valves (SVs) to obtain large MR outputs for the read sensor applications. The exchange biased SV with Co
₂
Fe(Al
_0.5
Si
_0.5
) alloy showed a resistance change-area product (ΔRA) of 6 m Ωμm
²
and an MR ratio of 21% at room temperature when the Co
₂
Fe(Al
_0.5
Si
_0.5
) layer was well-B2-ordered by a high temperature annealing at 500°C. The critical bias current density for the spin torque effect on the reduction of ΔRA was ~ 3 × 10
⁷
A/cm
²
. Based on the high spin polarization directly measured by the point contact Andreev reflection method, Co
₂
(Cr
_0.1
Fe
_0.9
)Si, Co
₂
Mn(Ga
_0.5
Sn
_0.5
), and Co
₂
Fe(Ge
_0.5
Ga
_0.5
) alloy thin films were investigated for CPP-GMR SVs. Among them, the Co
₂
Fe(Ge
_0.5
Ga
_0.5
) alloy showed a high CPP-GMR ratio in the pseudo SVs exceeding 40% at RT and 120% at 10 K.