A study of magnetic tunability in a superconductor coplanar resonator using a calcium, vanadium and garnet ferrite

Magnetic tunability of superconducting passive microwave devices can be done by modifying the characteristics of the medium surrounding the superconductor-based devices, in which the RF signal propagates. The variation of the permeability of a magnetic material by a DC magnetic field can achieve this objective. The magnetic material can be a ferrimagnetic material, such as a ferrite. An external DC magnetic field is used to modify the permeability of the ferrite and thus the propagation conditions. A YBCO based coplanar resonator having a resonant frequency at 5.6 GHz was used in this study. A ferrite made of calcium, vanadium and garnet (CVG) was chosen because its properties are expected to match those of YIG better for this experiment. Several positions of CVG ferrite were tried in order to get a good compromise between modulation and degradation of the properties. In the presence of a CVG plate of 500 μm thickness, at a distance of 400 μm from the superconductor, a displacement of 18 MHz of the resonant frequency has been observed for an applied field of 100 G at 77 K