Magnetic, temperature, and corrosion properties of the NiFe/IrMn exchange couple

Abstract

Exchange biasing properties of the NiFe/IrMn exchange couple were investigated by varying the IrMn composition and sputtering conditions. At a composition of Ir20Mn80 an exchange field of ∼60 Oe and a coercivity of 8 Oe were obtained for the structure Si/Ta-75 Å/NiFe-250 Å/IrMn-500 Å. The maximum exchange field obtained was similar for rf diode, rf magnetron, and dc magnetron sputtering of the IrMn. X-ray diffraction measurements showed that the crystalline texture was (111) for both the NiFe and IrMn, but a strong crystalline texture did not necessarily correspond to a large exchange field. The interfacial exchange energy, Jk, was evaluated to be 0.145 erg/cm2 and the minimum thickness of IrMn needed to support an exchange field was 75 Å. The blocking temperature was measured to be a function of the IrMn thickness and was in the range of 220–250 °C for thicknesses >200 Å. Below this, the blocking temperature rapidly decreased to a value of 130 °C at 75 Å of IrMn. Corrosion testing was done in a Battelle Class II type corrosive environment. Using the exchange field as a figure of merit, it was found that the IrMn corrosion properties were only slightly better than FeMn, and significantly worse than NiMn and CoNiO. We were also able to successfully fabricate NiFe based spin-valves pinned with IrMn and they show good magnetic properties. Our results show than IrMn is a good alternative to FeMn.