Magnetic-decoration imaging of structural transitions induced in vortex matter

During the last two decades, vortex structural transitions in type-II superconductors have been the subject of a considerable amount of theoretical and experimental studies. This article presents an exhaustive review of reports on real-space imaging of vortex structural transitions induced by introduced pinning potentials. The focus is set on the application of the magnetic-decoration technique to image structural transformations in three-dimensional vortex matter. Technical details, open issues and selected results in the paradigmatic high-and low-T-c materials Bi2Sr2CaCu2O8 and NbSe2 are presented. The role played by substrate disorder, nucleation and growth dynamics of the vortex solid, elastic properties and anisotropy of vortex matter is analysed.