Of Mram With Perpendicular Magnetic Anisotropy Spin Valve Performance Optimization Study

Spin valves with perpendicular magnetic anisotropy (PMA) have attracted intense interests as a promising candidate for applications in the magnetoresistive random access memory (MRAM). In this thesis, we put forward two methods to improve the performance of spin valves with PMA. Firstly, we took advantage of a synthetic antiferromagnet (SAF) structure with perpendicular anisotropy. Then, we made use of a perpendicularly exchange-coupled composite structure, consisting of a [Co/Ni]N multilayer and a ferrimagnetic TbCo layer.The main results in this thesis are as follows:Firstly, we successfully prepared perpendicularly magnetized synthetic antiferromagnet (SAF) in a structure of [Co/Ni]N/Ru/[Co/Ni]3. We studied the dependence of magnetic properties on layer repetition number and Ru thicknesses. The optimum SAF structure with strong antiferromangetic coupling field and large switching field of the net magnetization have been determined and was utilized as the reference layer in the pseudo spin valves. Compared with the rapid drop of GMR signal in the normal [Co/Ni]-based pseudo spin valves after annealing at low temperature of 150℃, the spin valve with SAF reference layer exhibits much stable thermal stability due to the large switching field difference between the free and reference layers which avoids the simultaneous magnetization rotation. The GMR signal of the SAF spin valve sample is 6.0% at room temperature, it decreases very gradually with further increasing Ta. We attribute the slow GMR reduction observed in the SAF spin valve to the effects of domain formation and perpendicular anisotropy deterioration caused by high temperature anneals.Secondly, we have investigated the exchange coupling interactions between the perpendicularly magnetized [Co/Ni]N and TbCo layers for various TbCo compositons. Perpendicular spin valves with Tb-rich [Co/Ni]N/TbCo reference layer are fabricated, which displays specific features. By slightly raising the TbCo thickness, the coercivity of the coupled structure greatly increases, thereby giving an effective way to widen the difference in switching fields for the free and reference layers, and making it possible to manipulate magnetization parallel or antiparallel for a wide range of fields. Such composite reference layer can not only retain a high perpendicular GMR ratio, but it also minimizes the field offset in the minor GMR curves due to the negligible stray field generated by the antiferromagnetically aligned moments in the reference layer.