  Incorporating cavity magnonics has opened up a new avenue in controlling
non-reciprocity. This work examines a yttrium iron garnet sphere coupled to a
planar microwave cavity at milli-Kelvin temperature. Non-reciprocal device
behavior results from the cooperation of coherent and dissipative coupling
between the Kittel mode and a microwave cavity mode. The device's
bi-directional transmission was measured and compared to the theory derived
previously in the room temperature experiment. Investigations are also
conducted into key performance metrics such as isolation, bandwidth, and
insertion loss. The findings point to the coexistence of coherent and
dissipative interactions at cryogenic conditions, and one can leverage their
cooperation to achieve directional isolation. This work foreshadows the
application of a cavity magnonic isolator for on-chip readout and signal
processing in superconducting circuitry.
