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

The present study illustrates the efficacy of using surface modifiers, or s imply surfactants, to alter, modify, or control the nature of interfaces an d film morphology in order to control physical properties in magnetic multi layers. In particular, the magnetic properties of giant magnetoresistive Ni O-Co-Cu-based symmetric spin valves are discussed in relation to the modifi cation of interfaces and nanostructure using surface modifier Pb. Results s how that a ML of Pb deposited on the first Co/Cu bilayer of the symmetric s pin valve leads to reduced in-plane magnetic anisotropy and coupling. In th e presence of Pb, the coherent growth mode of Co-Cu layers is disrupted, le ading to a fine grain size (approximate to 1-5 nm) in the metal layers. Alt hough this grain size corresponds to the critical wavelength for maximum co upling due to Neel's so-called "orange-peel" effect, the absence of topogra phical correlation between various interfaces prevent the occurrence of thi s form of coupling. At the same time, averaging of exchange interactions ov er such a fine grain size, which is much lower than the characteristic exch ange length for Co (approximate to 25-45 nm), precludes the display of loca l magnetocrystalline easy axes, thereby leading to low switching fields. Th e nature of magnetization reversal in the "free" Co layer of the Pb-free sp in valve is highly local in nature and occurs by nucleation, growth and coa lescence together of irregular micron or sub-micron sized domains. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reser ved.