The dominance of paramagnetic loss in microwave dielectric ceramics at cryogenic temperatures

Abstract

Commercial manufacturers add transition metals and other impurities to high performance microwave ceramic compounds to improve their manufacturability. Measurements of microwave loss tangent were performed on Ba(Zn 1/3Ta2/3)O3, ZrTiO4-ZnNb 2O6, Ba(Zn1/3Nb2/3)O3, and BaTi4O9-BaZn2Ti4O11 ceramics. A marked increase in the loss at low temperatures is found in materials containing transition metal with unpaired d-electrons as a result of resonant spin excitations in isolated atoms (light doping) or exchange coupled clusters (moderate to high doping). The loss tangent can be drastically reduced by applying static magnetic fields. Our measurements also show that this mechanism significantly contributes to room temperature loss, but does not dominate. © 2012 American Institute of Physics.