Magnetically tuning the loss tangent in La(Al_(1-x)Fe_x)O_3 using low field electron paramagnetic resonance transitions

摘要

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 Al_2O_3 (ε_r = 9.8) dielectric ceramics between a low-loss "on state" and a high-loss "off state" at frequencies of ～12 and ～19 GHz with a small magnetic field (＜100 G). In this report, we extend our work on smart materials to the large dielectric constant (ε_r = 24) host La(Al_(1-x)Fe_x)O_3 so that it can be used in compact resonator and filter designs operating at ～4 GHz to ～7 GHz. The Fe~(3+) 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(-6.467 MHz) and B_4~3 (160 MHz). These switchable dielectrics may have applications in future communication and Doppler technology.