Enhanced exchange biasing in ion-beam sputtered bottom spin-valve films

IrMn exchange biased bottom spin-valve films of structure Ta/underlayer/IrMn/CoFe/Cu/CoFe/NiFe/Ta were prepared using ion beam deposition techniques. The exchange bias field exhibits strong underlayer thickness dependence. For the first time, a large exchange energy of 0.29 erg/cm² was measured in spin-valve films exchange biased by a disordered antiferromagnet, comparable to the values usually obtained in spin valve films exchange biased by an ordered antiferromagnet. We have conducted a comparative study on both bottom and top exchange biased spin-valve and ferromagnetic/antiferromagnetic bilayer films. The results indicate that the exchange field obeys very well the inverse pinned layer thickness law over a thickness range from 200 Å down to 10 Å. The exchange energy for bottom spin-valve films is, however, a factor of two larger than that for top spin-valve films. When normalized, the exchange field exhibits the same temperature dependence for both bottom and top spin valve films. The enhancement in exchange biasing is mainly attributed to an enhanced texture for fcc (111) crystallographic orientation of the IrMn layer in bottom spin-valve films