Effects of Mn corrosion on the magnetic properties of Ni81Fe19/Ir20Mn80 exchange biased thin films

The effects of antiferromagnetic corrosion on the magnetic properties of exchange biased thin films were studied. A Ni81Fe19/Ir20Mn80 bilayer was grown using DC sputtering. The crystal structure, microstructure, and magnetic properties of the samples were examined using x-ray diffraction (XRD), scanning electron microscope along with energy dispersive spectrometer, and resonance-vibrating sample magnetometer, respectively. XRD patterns revealed that the crystalline structure was (111) for both IrMn and NiFe layers. After magnetic field cooling, the room-temperature exchange bias field and coercive field were determined from hysteresis loops and no training effect was observed during the remagnetization process. The magnetic properties of the exchange biased bilayer strongly depended on the level of Mn corrosion in deionized (DI) water. A step-like magnetization curve was observed in the bilayer after soaking in DI water for 10 min. A detailed analysis of the magnetic moment response indicated an increase in the depth and area of corroded Mn with increasing soaking time. Trace amounts of Mn2+ in DI water, detected by a spectrophotometric technique using 1-(2-pyridylazo)-2-naphthol as an indicator, confirmed increasing Mn corrosion with increasing soaking time.