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.