The thermal stability of the MnIr/NiFe exchange couple in the pinned electrode of a magnetic tunnel junction was analyzed using Auger electron spectroscopy and X-ray photo-electron microscopy. When the Ta/AlOx/CoFe/MnIr/NiFe/Ta/SiO2/Si electrode was annealed at 350C, the magnetic properties of the electrode quickly deteriorated. Auger electron spectroscopic analysis indicated that there was a large diffusion of Ni into the MnIr layer accompanied by Ir migration into the NiFe layer above 350C. X-ray photo-electron microscopy of the annealed electrode revealed that the massive migration of Ni resulted in the formation of antiferromagnetic NixMn1–x within the MnIr layer. The presence of the AlOx tunnel barrier, which promoted the preferential migration of Mn, appears to be the cause of the massive migration of Ni via the formation of vacancies in the MnIr lattice.

Interdiffusion in MnIr/NiFe Exchange Biased Layer Annealed above 300C in the Pinned Electrode of a Magnetic Tunnel Junction. C.S.Yoon, J.H.Lee, C.K.Kim: Journal of Applied Physics, 2003, 93[11], 8910-3