Development of magnetically switchable high permittivity microwave dielectrics using La(Al1-xFex)O3

The introduction of transition metal doping, particularly Fe³⁺, into high-performance microwave dielectrics can make “smart” materials that switch between a high-Q, low loss state and a low-Q, high loss state using a small external magnetic field. In this study, the dielectric and magnetic properties of the high permittivity host material LaAlO₃ (ε_r = 22.5), when doped with Fe³⁺, are reported. Spin losses dominate the loss tangent at cryogenic temperatures and survive up to room temperature. Peaks in the loss tangent versus temperature relation are observed near 40, 75, and 215 K. Additional measurements of samples exposed to annealing in varying environments, combined with Debye analysis and the results of native defect energy predictions from density functional calculationsPhys Rev B. 2009;80:104115], allows us to associate the 40, 75, and 215 K peaks to the following reactions, , , and , respectively.