New ternary ferromagnetic phase induced by annealing at the FeMn/Co/FeMn interfaces

The thermal stability of the antiferromagnetic FeMn pinning layer is invest igated. High-vacuum annealing treatments at different temperatures on the T a/Cu/FeMn/Co/FeMn/Ta thin films, prepared at room temperature on silicon su bstrate, have been performed. The most interesting result is observed after annealing at 280 degreesC. A strong decrease in the interfacial exchange a nisotropy is observed together with a strong increase (about 50%) of the sa turation magnetization. Nuclear magnetic resonance measurements performed o n the as-deposited and annealed sandwiches have shown that the observed cha nge is due to the formation of a new ferromagnetic FeMnCo phase at the FeMn /Co interfaces. (C) 2001 Elsevier Science B.V. All rights reserved.