High precision ac susceptometer for measuring the temperature and magnetic field dependence of the penetration depth in superconductor single crystals

An ac susceptometer has been developed for very sensitive measurement of the magnetic moment of small samples as a function of temperature and applied dc field. The system was designed specifically for measurements on small single crystals of the high T-c superconductor YBa2Cu3O7-delta in the Meissner state. The natural platelet geometry of these crystals allows results to be easily transcribed into changes in the material's magnetic field penetration depth, Delta lambda, an important quantity in the exploration of the underlying physics of its superconductivity. The resolution of the technique is of the order of one tenth of an angstrom for a sample of area similar to 2 mm(2). (C) 2000 American Institute of Physics. [S0034-6748(00)00911-4].