Magnetically tuning the loss tangent in La(Al1-xFex)O3 using low field electron paramagnetic resonance transitions

In 2012, we demonstrated that microwave loss in practical microwave dielectrics is dominated by electron paramagnetic resonance transitions at cryogenic temperatures. We later used this understanding to develop smart materials that switch Fe-doped Al2O3 (epsilon (r) = 9.8) dielectric ceramics between a low-loss on state and a high-loss off state at frequencies of similar to 12 and similar to 19GHz with a small magnetic field (<100G). In this report, we extend our work on smart materials to the large dielectric constant ((r) = 24) host La(Al1-xFex)O-3 so that it can be used in compact resonator and filter designs operating at similar to 4GHz to similar to 7GHz. The Fe3+ ions' zero-field splitting energies are determined by the crystal-field parameters D=1.55GHz and E=0GHz, along with significant contributions from the higher-order terms, B 4 0(-6.467MHz) and B 4 3 (160MHz). These switchable dielectrics may have applications in future communication and Doppler technology.