Influence of columnar defects on magnetic relaxation of microwave nonlinearity in superconducting YBCO resonator devices

•Distortion of the microwave signal in a high temperature superconducting microwave resonator relaxes upon removal of an external magnetic field.•The relaxation corresponds to flux relaxation with a rapid exponential expulsion of excess fluxons followed by a slow logarithmic thermally activated decay over the surface barrier.•Introduction of columnar pinning centers by heavy ion beam irradiation eliminates the rapid expulsion process with the remaining slow logarithmic process likely influenced by flux hopping. Intermodulation distortion (IMD) of microwave signals incident upon a superconducting YBa2Cu3O7−x thin film sample on a LaAlO3 substrate is shown to relax as the sample magnetization also relaxes, revealing the signature of fluxon decay in the microwave distortion. The sample contained a microchannel of columnar defects that was introduced using heavy ion beam irradiation. After exposure to and then removal of a low strength static magnetic field, IMD relaxed due to thermal activation of fluxons over the surface barrier. This process influenced second and third order IMD differently, visible in the differing functional form of the IMD in time and the temperature dependence of the relaxation function. The presence of columnar defects in the test sample suppressed thermal activation by pinning of fluxons, notably with complete suppression of relaxation in third order IMD at low temperatures. Higher order IMD was found to relax with the same functional form as the second and third order IMD of the same parity.