Temperature dependence of the magnetic field penetration depth in YBa2Cu3O7−δ measured on ultra fine powder

Abstract The temperature dependence of the magnetic field penetration depth λ( T ) in superconducting YBa 2 Cu 3 O 7−δ has been determined by measuring the AC susceptibility of fine powder at the frequency 10 5 Hz. The reason for noticeable changes in λ at low temperatures has been found out: strong scattering of carriers by low-frequency excitations. The coupling constant which controls the superconductivity has been estimated. At low temperatures a paramagnetic signal superimposed to the superconductivity one has been observed. It is probably due to alteration in the interaction of the magnetic moments near the surface of the particles.