Spin-valve giant magnetoresistance films with antiferromagnetic PtPdMn

The antiferromagnetic alloy Pt20Pd30Mn50 has demonstrated a high exchange coupling field to a coupled NiFe film as well as high corrosion resistance, making it a promising candidate for use as the pinning layer of a spin valve. In this work we have investigated the magnetic and structural properties of spin-valve films exchange biased by CoFe/PtPdMn as compared to CoFe/IrMn spin valves. A spin-valve film structure of Ta50 Å/NiFe50 Å/CoFe20 Å/Cu28 Å/CoFe22 Å/PtPdMn300 Å/Ta50 Å annealed at 250 °C for 10 h showed a giant magnetoresistance of 6.5% with an exchange field of 680 Oe. The blocking temperature of this film is about 350 °C, compared to 250 °C for IrMn based spin valves. The remnant blocking temperature was also measured, and showed that for PtPdMn spin valves the exchange field was constant up to a temperature of 300 °C, in contrast to 180 °C for an IrMn spin valve. Structural ordering of the PtPdMn in a face-centered-tetragonal (fct) phase after annealing has been observed using x-ray diffraction and transmission electron microscopy. The x-ray diffraction data exhibits a strong face-centered-cubic (111) and fct (111) out-of-plane orientation for as-deposited and annealed samples. Transmission electron micrographs show a smooth interface between the PtPdMn and CoFe layers, columnar growth structure, and fct ordering of the PtPdMn.