Field dependent alternating current susceptibility of metalorganically deposited YBa2Cu3O7−δ films

The field amplitude and frequency dependent complex alternating current susceptibility χ(Hm, f) of YBa2Cu3O7−δ films metalorganically deposited on different substrates with different processes has been measured at 77 K and studied in relation with their microstructures and some modeling results. It is shown that χ(Hm) for films with well aligned grains and a high Jc is of Bean type with a characteristic f dependence for a power-law E(J), so that thermally activated collective flux creep is the dominant dissipation mechanism. The Jc of these films may be well determined by χ(Hm, f) measurements. For films with misaligned grains and intermediate values of Jc, χ(Hm, f) is anomalous and able to be roughly simulated by a linear-exponential E(J). This phenomenon should be related to the presence of weak links and Josephson vortices, but to look for its physical mechanism is still challenging.