Spin-Valve GMR Films Based on Antiferromagnetic NiMn

Abstract

ABSTRACTIn this work we have investigated the magnetic and structural properties of spin-valve films exchange biased by CoFe/NiMn compared to CoFe/lrMn spin valves. A spin-valve film of structure Ta/NiFe/CoFe/Cu/CoFe/NiMnITa showed a giant-magnetoresistance of 5.5% with a Hex∼850 Oe after annealing. Structural ordering of the NiMn in an fct phase after annealing has been observed using x-ray diffraction, with the data exhibiting pure fct(111) texture. The thermal stability of both the exchange pinning and magnetoresistance of NiMn spin-valves was evaluated. The blocking temperature (Tb) of this film is 400°C, compared to 225°C for IrMn based spin-valve films (IrMn thickness ∼50 Å). Blocking temperature distribution and remnant blocking temperature measurements also suggest that NiMn based spin-valves have far superior pinning stability with temperature than IrMn based spin-valves. Magnetoresistance measurements show a linear decrease with temperature due to electron-phonon scattering with the ∆R/R being reduced by 33% at 150°C (as compared to a 50% decrease for IrMn based spinvalves). Extended annealing at 150°C did not effect spin-valve performance, with ∆R/R and R being constant over 60 hours, suggesting that no appreciable interdiffusion is occurring.