Dependence of Exchange Bias Field on Thickness of Antiferromagnetic Layer in NiFe/IrMn Structures

Magnetic properties of ferromagnetic/antiferromagnetic thin-films structures for spin-valve applications have been studied. Multilayer structures of Ta/Co/IrMn/Ta and Ta/FeNi/IrMn/Ta were deposited on Si substrate at room temperature by DC magnetron sputtering. Thickness of the antiferromagnetic layer changed from 10 to 50 nm. The coercive force was found to be non-monotonic function of the antiferromagnetic layer thickness. The exchange bias for 30-50 nm antiferromagnetic layers (73 Oe) is about 10 Oe larger than for 10-20 nm antiferromagnetic layers. Moreover, it was demonstrated that the alternative sequence of the deposition (antiferromagnetic layer on the top or below the ferromagnetic layer) leads to dramatic changes of structures magnetic properties.