Magnetic properties of antiferromagnetically coupled CoFeB/Ru/CoFeB
  This work reports on the thermal stability of two amorphous CoFeB layers coupled antiferromagnetically via a thin Ru interlayer. The saturation field of the artificial ferrimagnet which is determined by the coupling, J, is almost independent on the annealing temperature up to more than 300 degree C. An annealing at more than 325 degree C significantly increases the coercivity, Hc, indicating the onset of crystallization. 
N. Wiese, T. Dimopoulos, M. Ruhrig, J. Wecker, H. Bruckl, G. Reiss