Atomic engineering of giant magnetoresistance spin valves using surfactants.

摘要

Giant magnetoresistance (GMR) magnetic multilayers have been one of the most attractive research topics with the most intense research efforts around the world.; In the present study, effects of various coupling mechanisms in GMR spin valves (SV) were studied. Switching dynamics of spin valves and each permutation which make up a spin valve, were systematically and intensively investigated by real time domain structure analysis. Magnetic behavior and dynamics of domain structure were intensively studied by applying the interference-contrast colloid (ICC) technique. A complete set of the coupling mechanism system was thus established for a GMR SV to explain the enhanced coercivity qualitatively and the strength of exchange coupling quantitatively. To control the microstructure, and in order to modify magnetic properties of spin valves, atomic engineering using surfactants was introduced and the efficiency of surfactants was investigated. Ag and Pb-Ag were selected as the surfactants to significantly alter the interfacial characteristics and to improve the GMR effect dramatically. In plane magnetization and GMR loops were measured for both surfactant free and surfactant containing samples. Conventional transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), and in-situ scanning tunneling microscopy (STM) were employed to analyze the relationship between characteristics of crystal, surfaces, interfaces and magnetic properties, such as GMR ratio, coercivity, H_c, and exchange coupling, H _E. Roughness induced pinholes were discovered, especially in surfactant free GMR spin valves. A new statistical model that takes into account topographic characteristics of the spacer was developed to evaluate the strength of pinhole coupling quantitatively. The effectiveness of the statistical model was discussed and compared to the experimental data that were obtained from spin valves with different interfacial characteristics. (Abstract shortened by UMI.)