Study On Exchange Bias Of IrMn/[Co/Pt] System With Ultra-thin Pt Layers And NiFe/FeMn System

The exchange bias in antiferromagnet/ferromagnet films,which has attracted a great deal of attentions in condensed matter physics,plays a key role for manipulating the spin orientation in magnetoelectronic devices such as spin valve and magnetic tunnel junction.In this dissertation,we have studied the exchange bias property of IrMn/[Co/Pt]and NiFe/FeMn film systems,and the relation of exchange bias to magnetic anisotropy and field cooling direction.The IrMn/[Co/Pt]multilayers with ultra thin Pt layers?⁵.0??were deposited.It is found that for as-deposited state,these samples have no perpendicular exchange bias and exhibit in-plane anisotropy.After perpendicular field cooling,perpendicular exchange bias is generated with the anisotropy axis rotating towards perpendicular direction.A well-defined perpendicular and large perpendicular exchange bias can be achieved by optimizing the thickness of Co layers,and the perpendicular anisotropy originating from IrMn/Co interface is found to be much larger than that of Co/Pt interfaces.By replacing Co in contact with IrMn with Co₆₀Fe₄₀/Co bilayer,the perpendicular exchange bias is enhanced twofold with the perpendicular anisotropy significantly weakened.The perpendicular exchange bias in this dissertation is much larger than that of previously reported counterparts which contain relatively thick Pt layers.It is also demonstrated that the value of perpendicular exchange bias is independent of the magnetic anisotropy of ferromagnet.In this dissertation,the exchange bias of NiFe/FeMn with no sufficient crystallization and texture was investigated,it is found that there is no exchange bias at room temperature.By field cooling to 2 K,the exchange bias can be established along both perpendicular and in-plane direction.The perpendicular exchange bias is highly identical with the in-plane one at the temperature of 2³0 K,which may be attributed to the absence of crystallization and texture which yields a random orientation of uncompensated spin of antiferromagetic phase in Fe Mn,but becomes larger than the in-plane bias at the temperature above 30 K.