Magnetic field-induced degradation of magnetic properties in molecular beam epitaxy grown FeMn/NiFe exchange-coupled bilayers

Degradation of magnetic properties has been observed in molecular beam epitaxy grown Si(111)/Cu 2 nm/NiFe 6 nm/FeMn (2–12)nm/Cu 5 nm exchange-biased bilayers during magnetic field sweeping. When the samples are subjected to several magnetic field sweeps, there is blister-shaped deterioration of the film surface quality and the magnetometry data suggest an increasing fraction of the NiFe moments become unpinned from the FeMn layer. Comprehensive characterization using high resolution electron microscopy and electron probe microanalysis revealed that this degradation has been initiated by delamination between the NiFe and FeMn layers and crack formation as a result of magnetostrictive stress buildup during the magnetic field sweeps. Further degradation can then be attributed to the formation of the nonmagnetic FeMn oxide by oxidation of the bare FeMn around the delaminated area.