Exchange coupling between an amorphous ferromagnet and a crystalline antiferromagnet

We have investigated the exchange bias effect in bilayers of an amorphous ferromagnet (CoFeB) and a crystalline antiferromagnet (IrMn) in a top-pinned configuration. When the crystalline IrMn layer was deposited on top of the amorphous CoFeB layer, no exchange bias was observed. On insertion of a thin crystalline ferromagnetic layer of NiFe between the amorphous CoFeB and the crystalline IrMn, exchange coupling appeared and it was dependent on the thickness of the NiFe layer. An enhancement in the blocking temperature of the CoFeB/NiFe/IrMn layers was observed on increasing the thickness of the NiFe layer. These effects were directly correlated with the (111) texture in the antiferromagnetic phase of the IrMn layer, which developed progressively with increasing thickness of the NiFe layer. The blocking temperature was found to vary linearly with the intensity under the (111) IrMn X-ray diffraction peak. A NiFe interlayer can be used to introduce an additional source of anisotropy in a giant magnetoresistance sensor, by exchange coupling the free ferromagnetic (FM) layer of CoFeB in an orthogonal direction to the anisotropy direction of the pinned FM layer.