Exchange coupling of radio frequency sputtered NiMn/NiFe and NiFe/NiMn bilayers

Exchange coupling of radio frequency sputtered NiMn/NiFe (NiMn on top) and NiFe/NiMn (NiMn at bottom) bilayers have been investigated. It was found that the exchange coupling field, H-ex, is not only directly related with the annealing temperature and time, but also is greatly influenced by the thin film deposition conditions. It was demonstrated that successful antiferromagnetic-ferromagnetic bilayer preparation should avoid interfacial contamination, which could destroy the spin coupling at the interface. The NiFe/NiMn bilayers show a high exchange coupling field [307 Oe for NiFe(200 Angstrom)/NiMn(500 Angstrom)] bilayer with a high blocking temperature around 430 degrees C. Most important is that the coupling field was able to sustain its strength up to almost 270 degrees C before starting to decrease. X-ray diffraction reveals that the diffraction intensity of NiMn in as-deposited bilayers does not seem important to achieve a high exchange coupling field. Furthermore, the NiMn thickness dependence of the magnetic properties of NiMn/NiFe bilayer and the NiFe thickness dependence of magnetic properties of NiFe/NiMn bilayers have been investigated and explored. (C) 1999 American Institute of Physics. [S0021-8979(99)33708-7].