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 Fe${}^{3+}$ 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 and 10 K, depending on the Fe${}^{3+}$ 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.

• Received 16 September 2011

DOI:https://doi.org/10.1103/PhysRevB.85.075122