nano - oxide based current - perpendicular - to - plane magnetoresistive sensor stacks are provided , together with methods for forming such stacks . such stacks have increased resistance and enhanced magnetoresistive properties relative to cpp stacks made entirely of metallic layers . said enhanced properties are provided by the insertion of magnetic nano - oxide layers between ferromagnetic layers and non - magnetic spacer layers , whereby said nano - oxide layers increase resistance and exhibit spin filtering properties . cpp sensor stacks of various types are provided , all having nano - oxide layers formed therein , including the spin - valve type and the synthetic antiferromagnetic pinned layer spin - valve type . said stacks can also be formed upon each other to provide laminated stacks of different types .