Interface tailoring effect for Heusler based CPP-GMR with an L1₂-Type Ag₃Mg spacer

Current perpendicular-to-plane (CPP) giant magnetoresistance (GMR) effects are of interest in a possible application of magnetic sensor elements, such as read-head of hard disk drives. To improve the junction performance, the interface tailoring effects were investigated for the Heulser alloy, Co₂Fe_0.4Mn_0.6Si (CFMS), based CPP-GMR junctions with an L1₂-Ag₃Mg ordered alloy spacer. Ultra-thin Fe or Mg inserts were utilized for the CFMS/Ag₃Mg interfaces, and CPP-GMR at low bias current density, J and the J dependence were evaluated for the junctions. Although, at low bias J, MR ratio decreased with increasing the inserts thickness, the device output at high bias J exhibited quite weak dependence on the insert thickness. The output voltages of the order of 4 mV were obtained for the junctions regardless of the insert at an optimal bias J for each. The critical current density J_c was evaluated by the shape of MR curves depending on J. J_c increased with the insert thicknesses up to 0.45 nm. The enhancement of J_c suggests that spin-transfer-torque effect may reduce in the junctions with inserts, which enables a reduction of noise and can be an advantage for device applications.