5 - Magnetic Properties

Abstract

This chapter discusses the magnetic properties of the superconductors. A material in the mixed state of a Type II superconductor contains magnetic flux in vortices that are embedded in a superconducting matrix. This chapter analyzes the parallel geometry case of a superconductor in the shape of a long cylinder located in an applied field directed along its axis. It is found that the hysteresis loops are thin and linear when the scan range is much less than the lower-critical field and when the temperature is close to critical temperature. The chapter also examines magnetic properties of a perfectly diamagnetic material with a hole that is either open or closed to the outside. It is found that for field cooling, the magnetic field is trapped in the open hole, while surface currents shield the superconductor itself and the enclosed cavity from this field, which gives for the magnetic moment. The magnetic properties of high-temperature superconductors are highly anisotropic, with magnetization and susceptibility depending on the angle that the applied field makes with the c-axis. When the transition is sharp, resistivity can drop sharply to zero at a temperature slightly above the onset of the susceptibility or magnetization transition.