Magnetic behavior of atomically engineered NiO–Co–Cu-based giant magnetoresistance spin valves using Pb as a surface modifier Original Research Article

The present study illustrates the efficacy of using surface modifiers, or simply surfactants, to alter, modify, or control the nature of interfaces and film morphology in order to control physical properties in magnetic multilayers. In particular, the magnetic properties of giant magnetoresistive NiO–Co–Cu-based symmetric spin valves are discussed in relation to the modification of interfaces and nanostructure using surface modifier Pb. Results show that a ML of Pb deposited on the first Co/Cu bilayer of the symmetric spin valve leads to reduced in-plane magnetic anisotropy and coupling. In the presence of Pb, the coherent growth mode of Co–Cu layers is disrupted, leading to a fine grain size (≈1–5 nm) in the metal layers. Although this grain size corresponds to the critical wavelength for maximum coupling due to Néel’s so-called “orange-peel” effect, the absence of topographical correlation between various interfaces prevent the occurrence of this form of coupling. At the same time, averaging of exchange interactions over such a fine grain size, which is much lower than the characteristic exchange length for Co (≈25–45 nm), precludes the display of local magnetocrystalline easy axes, thereby leading to low switching fields. The nature of magnetization reversal in the “free” Co layer of the Pb-free spin valve is highly local in nature and occurs by nucleation, growth and coalescence together of irregular micron or sub-micron sized domains.