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The magnetic flux structure in type-II superconductors was predicted in 1957 by Abrikosov [5.1]. According to that theoretical work the magnetic field penetrates into a superconductor in the form of individual magnetic lines (vortices) each carrying one magnetic flux quantum Ф0 = hc/2e = 2.07.10−7 G.cm2. The idea of a vortex state proved to be extremely valuable in explaining electrodynamic properties of type-II superconductors. The most convincing evidence of the validity of this theory was the direct observation of the Abrikosov vortices using the high-resolution technique of decoration with dispersed ferromagnetic particles. This technique was developed in 1966 by Traumble and Essmann in Stuttgart [5.2]. Their works marked the beginning of magnetic structure investigations in conventional low-Tc type-II superconductors; the results have been summarized in reviews and monographs [5.3,5].