We investigated the relation between the background pressure (PB.G.) of the sputtering chamber and the unidirectional anisotropy field (Hua) of spin-valve films with PdPtMn antiferromagnetic layers fabricated by an ultrahigh vacuum (UHV) sputtering process. Hua increased with decreasing PB.G. until PB.G. reached 2 × 10-7 Pa. The UHV sputtering process helped to reduce the PdPtMn thickness from 25 nm, which was needed in the conventional high-vacuum (HV) sputtering process, to under 15 nm while preserving the magnitude of Hua. We fabricated a spin-valve structure with total thickness of 26.5 nm exhibiting a large MR ratio over 8.0%, sufficient Hua (>500 Oe), and large sheet resistance change (Δρ/ttotal = 1.6 Ω).
