Development of magnetically switchable high permittivity microwave dielectrics using La(Al_1‐xFe_x)O₃

Abstract

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 (εr = 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 calculations[Phys Rev B. 2009;80:104115], allows us to associate the 40, 75, and 215 K peaks to the following reactions, normalOnormalinormalx+normalVnormalOnormalx→normalOnormali′+normalVnormalO·, FeAlnormalx+normalVAl″→FeAl′+normalVAl′, and Alnormalinormalx+Alnormali··→2Alnormali·, respectively.