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/cm(2) 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 Angstrom down to 10 Angstrom. 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.