Magnetization Characterization of Superconductors

The superconducting state occurs for many elements, alloys, and compounds when cooled to sufficiently low temperatures, specifically, below the critical temperature, Tc. The initial discoveries by Onnes in 1911 and 1914 were of the loss of electrical resistance at very low temperatures and of its reestablishment by applying a strong enough magnetic field or a high enough current. A further discovery by Meissner and Ochsenfeld in 1933 was that a magnetic field could be expelled from a superconducting material as it was cooled through its Tc. This perfect diamagnetic behavior coupled with perfect conductivity led to the derivation of London equations describing the superconducting state in 1935. At present, there are many known superconducting materials ranging from pure elements such as lead, that are superconducting at liquid helium temperatures, to complex ceramics such as YBaCuO7-x operating at liquid nitrogen temperatures. Also, uses of superconductors vary enormously ranging from sensitive magnetic field detectors to electric power cables. Certain engineered superconducting materials and composites can carry very high transport currents in high magnetic fields and much research at this time is being devoted to the development of commercial and also power utility applications. The characterization of these technological materials is a very important part of these activities. Here, we present some basic features of magnetization characterization of superconductors, in particular high temperature superconductors. Keywords: superconductors; magnetism; magnetization; flux line pinning; critical currents; type II superconductors