A study was made to determine the effects of a double-soak sintering process on the saturation magnetization, Curie temperature and hysteresis properties of an Al-substituted MgMn-microwave ferrite. This process decreases saturation magnetization and magnetic induction, while increasing the loop squareness and the Curie temperature. The double-soak sintering process improves the properties of the ferrite for application in a low-microwave-frequency band (i.e. S-band) latching phase shifter. This improvement could not be achieved by increasing the Al3+ content, as this tends to reduce the Curie temperature, and thus decreases the thermal stability. The double-soak sintering process, however, enables a composition to be used which initially has a slightly higher saturation magnetization than the desired value.