The spin flop of synthetic antiferromagnetic films

The spin flop of synthetic antiferromagnetic pinned layers (SAF), under a magnetic field has been theoretically predicted and recently reported [J. G. Zhu and Y. Zheng, IEEE Trans. Magn. 34, 1063 (1998); J. G. Zhu, IEEE Trans. Magn. 35, 655 (1999)]. However, no experimental data have yet being reported to confirm the theoretical prediction. This article will provide direct experimental evidence to confirm the spin flop phenomenon in SAF layers. A spin valve, [CoFe/NiFe]/Cu/[CoFe(II)/Ru/CoFe(I)]/IrMn, was used to verify the spin flop in SAF layers. The exchange bias direction of CoFe(I)/IrMn was introduced by a magnetic annealing process at 225 degrees C with a field strength of H-an(10 kOe) and the exchange bias direction was found parallel to the magnetic field. These samples serve as the reference for the remaining experiments. By magnetic annealing the reference samples at 225 degrees C with lower magnetic fields, we found that the magnetic field threshold for SAF spin flop is about 1 kOe. When the field is further increased, the spins of CoFe(I) and CoFe(II) scissor toward the applied magnetic field axis and the moment of the SAF reaches saturation when the applied field is equal to or greater than 10 kOe. Thus the above experiments demonstrate the flop behavior of the SAF. It also provides direct evidence that the exchange bias direction between a ferro/antiferromagnetic interface is determined by the magnetization of the ferromagnetic layer, not by the magnetic annealing field. (C) 2000 American Institute of Physics. [S0021-8979(00)59308-6].