.nife / Ptmn Exchange Bias Phenomenon In The System

Due to the key role in application of spin-valve structure giant magnetoresistance (GMR), exchange bias effect has become an international hotspot recently. In this thesis,the exchange bias effect of NiFe/PtMn has been studied .Ta/Ni₈₁Fe₁₉/[Pt(6A)/Mn(x A)]_n/Ta films with different Mn thickness were prepared by using DC magnetron sputtering and the effect of the Mn composition on the exchange bias effect of the bilayers has been investigated. The results show that the exchange bias reaches a maximum value at x ≈ 56.1%,then decreases as x increases. XRD results show that antiferromagnetic equiatomic PtMn layer could be formed with reduced thickness and much shortened annealing time if PtMn layer is prepared with suitable excess Mn.Ta/Ni₈₁Fe₁₉/[Pt(tA)/Mn(tA)]n/Ta films have also been prepared and the effect of Pt and Mn layer thickness on the exchange bias of the films has been studied. After being annealed at 270 ℃ for 2 hours in a vacuum chamber, the samples with t=2A have large exchange bias. But the samples with t=12A exhibit exchange bias after being annealed at 300℃ for 2 hours .XRD results show that the thinner PtMn layer will be easily transformed into uniform PtMn alloy film with L1₀ phase.At the same time, we introduced Pt layer in the interface of the ferromagnetic and antiferromagnetic layers, which was proved to be very efficient to prevent Mn from further intruding into the ferromagnetic layer. As a result, the ferromagnetic layer pinned by PtMn layer exhibited excellent performance.Lastly, the structural and magnetic properties of NiFe/PtMn bilayers with Ta or NiFeCr as the seed and cap layers were investigated. It was found that the NiFe/PtMn bilayer with NiFeCr as seed and cap layers has higher exchange bias than that with Ta.After annealing; the magnetization reduction of the films with NiFeCr seed and cap layers was less than that with Ta seed and cap layers. On the other hand, the grain size of the bilayers with NiFeCr seed layer was much larger than that of the films with Ta seed layer, which leads to a better thermal stability for the former. The present results indicate that NiFeCr can be promising seed and cap layers in spin valves based on Mn-alloyed antiferromagnets.