  To create a stable signal from a cryogenic sapphire maser frequency standard,
the frequency-temperature dependence of the supporting Whispering Gallery mode
must be annulled. We report the ability to control this dependence by
manipulating the paramagnetic susceptibility of Fe3+ ions in the sapphire
lattice. We show that the maser signal depends on other Whispering Gallery
modes tuned to the pump signal near 31 GHz, and the annulment point can be
controlled to exist between 5 to 10 K depending on the Fe3+ ion concentration
and the frequency of the pump. This level of control has not been achieved
previously, and will allow improvements in the stability of such devices.
