Development of new type nano TOx-MgO (T=V, Ti) tunnel barrier for spin valve systems

This thesis involves the fabrication and characterization of MgO based spin valve (SV) systems for magnetic memory and position sensor applications. Magnetron sputtering (MS) method was used to deposit the layers of IrMn based exchange bias spin valve (EB-SV) systems and pseudo spin valve (P-SV) systems which have stacking structure without antiferromagnetic pinning layer. In the EB-SV systems, effect of buffer and seed layer on the structure and magnetic properties were investigated, and optimum stacking structure of EB systems were obtained. For the barrier layer, single layers were produced using different MS methods and a proper production technique was developed for that purpose. Having deposited the EB-SV systems, uni directional magnetic annealing (UDA) experiments were performed on the EB-SV systems, and optimum UDA temperature was found by investigation of structural and magnetic properties of the annealed EB-SV systems. The microfabrication of EB-SV systems were done using shadow masks. Optimized EB systems and barrier layer were integrated into an EB-SV system, and a TMR values of 98% was achieved at 1.8nm MgO thickness. As a complementary study, new generation and high performance MgO based P-SV systems were produced. Structural, magnetic, electrical and magnetoresistance properties of P-SV systems were systematically investigated to obtain the best performance in these systems. The Rowell criteria, are met for the P-SV which were microfabricated using lithography techniques. Additionally, dependence of P-SV on barrier thickness and resistance area was examined. As a result, microfabricated P-SV systems having 2 nm MgO thickness and resistance area about 25×25µm2shows 508% TMR value at room temperature. Moreover, effect of tunneling mechanism on the bias dependent TMR was found, and the Fowler Nordheim (FN) Tunneling effect was observed for the first time in P-SV systems, which may indicate that FN tunnelling represents the physical intersection between TMR and Giant magnetoresistance (GMR) effects which has nonmagnetic metalic spacer.