Levitation Forces Acting on an HTS Sample in the Field of a Permanent Magnet.

Using the Monte Carlo method, the vertical z-component of levitation force acting on a thin HTS film in a field simulating the inhomogeneous field of a permanent magnet is calculated within the framework of a two-dimensional model of a layered HTS. The dependences of the vertical component of the levitation force on the distance to the magnet are obtained at different concentrations of pinning centers and at temperatures ranging from 1 to 50 K. A case is simulated in which a superconducting sample starts moving towards a magnet from infinity and then moves away from the magnet. The change of sign of the levitation force corresponds to the movement away from the magnet when trapped magnetic flux is present in the sample. The presence of hysteresis of the levitation force is demonstrated. It is also shown that the levitation force does not change its sign in a defect-free sample and in a sample with a large number of defects. This is due to the peculiarities of the distribution of vortex density and currents in the sample during magnetization process. [ABSTRACT FROM AUTHOR]