The exchange coupling of a NiO/FeNi bilayer with interdiffused interface

A series of NiO(110 Angstrom)/FeNi(t(F) Angstrom)/Cu(24 Angstrom)/FeNi(t(F) Angstrom) spin-valve-structure samples were fabricated using ion beam sput tering. The exchange bias HE of the pinned FeNi layer increases as the FeNi thickness tF decreases. For t(F) < 70 Angstrom, however, H-E decreases wit h the decrease of t(F). The coercivity H-Cp varies as 1/t(F) at room temper ature. The M-H loops show that the magnetic moment of the pinned FeNi layer is smaller than that of the free FeNi layer, indicating that an FeNi layer of about 20 Angstrom is interdiffused with the NiO layer leading to a drop of the magnetic moment of the pinned FeNi layer. The interdiffusion betwee n the FeNi and NiO layers may account for the decrease of the exchange bias H-E for t(F) < 70 Angstrom.