Structural and magnetic properties of Fe/ZrO2 continuous and discontinuous multilayers

Fe/ZrO2 multilayers have been studied mainly by EXAFS and Moessbauer spectroscopy with the aim of understanding the low-magnetoresistance (MR) amplitude of this system compared with Co/ZrO2 multilayers. As-deposited thin iron layers (0.6-0.9 nm) are found to be amorphous or ill-ordered with Fe-Fe bond lengths slightly larger than in BCC iron. The discontinuity of the layers brings about a superparamagnetic contribution which is increased by annealing at 500 deg. C. Thick iron layers (>1.2 nm) are continuous whatever the annealing temperature. Non-magnetic Fe2+, Fe3+ sites account for at least 20% of the iron atoms in the as-deposited thin iron layers and up to 62% after annealing at 600 deg. C. The presence of these ions located near the interfaces can have drastic consequences on the spin-dependent tunnelling mechanism, that is, on the MR properties of the system