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

Abstract

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, Hex, 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 Å)/NiMn(500 Å)] bilayer with a high blocking temperature around 430 °C. Most important is that the coupling field was able to sustain its strength up to almost 270 °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.