Characterization of magnetic thin films used in magnetic random access memory

Exchange-biased magnetic layers, consisting of a ferromagnetic (FM) layer coupled to an antiferromagnetic (AFM) biasing layer, form an integral part of storage devices based on spin valves and magnetic tunnel junctions. Many attempts have been made to develop a satisfactory theory of exchange bias (EB), but these theories do not enable satisfactory predictions to be made about either the EB shift or the enhanced FM coercivity. A better model of exchange-coupled bilayers based on more comprehensive experimental results is needed.; The combined effect of several key variables on the structural, and especially magnetic, properties of exchange-coupled bilayers has been investigated here using a Design of Experiments (DOE) approach. Nickel Oxide (NiO) and Nickel Manganese (NiMn) AFMs deposited on Permalloy (Py − Ni₈₁Fe ₁₉), were used to evaluate the DOE study.; The AFM material and orientation were shown to be critical in determining the exchange field and coercive field. The presence of 7% Nitrogen partial pressure during Py deposition induced textured <200> growth, but <111> in its absence. Since the preferred orientation for AFM NiO is <111>, the highest exchange fields were measured for NiO/Py bilayers having this texture. Lorentz electron microscopy revealed that the primary magnetization reversal mechanism in <111>-textured NiO/Py EB bilayers was a domain wall sweeping across the field of view. In <200>-textured films, local areas had strong exchange coupling, and these acted as nucleation sites for domain reversal.; Reduced exchange fields were observed in NiO/Py EB bilayers as annealing temperatures were increased. Small probe microanalysis revealed interdiffusion at the Py/NiO interface, which most likely caused the exchange field reduction. There was also evidence for a magnetically dead layer at the Py/Ta interface, which reduced the magnetic moment, corresponding to reduction in the coercive field.; Lorentz electron microscopy and high resolution electron microscopy were used to measure magnetic domain wall widths and to observe the microstructure of Cobalt-Iron/native oxide multilayers. The effect of a Copper buffer layer on Iron (70%)-Cobalt (30%) domain-reversal mechanisms was investigated using Lorentz electron microscopy. Reduction in domain sizes due to the presence of the Cu buffer layer was observed.