Enhanced blocking temperature in NiO spin valves: Role of cubic spinel ferrite layer between pinned layer and NiO

We compare the blocking temperature for simple permalloy (80% Ni)/Au/permal loy/NiO spin valves with and without an interfacial, oxidized Fe layer (Fe layer 12 Angstrom thick) inserted at the permalloy/NiO interface. We find a significantly increased blocking temperature and pinning field for spin va lves with the interfacial Fe-oxide layer, as a result of moderate (230 degr ees C/1 h) annealing of the Au/permalloy/Fe-oxide/NiO part of the spin valv e. High resolution transmission electron microscopy and electron energy los s microanalysis reveal that the Fe-oxide layer is converted to a cubic spin el ferrite (Ni0.8Fe2.2O4) layer by solid state reaction with the NiO. (C) 2 000 American Institute of Physics. [S0003-6951(00)04234-0].