Linewidth Studies in Ordered Lithium Ferrite

Abstract

Linewidth measurements have been carried out in ordered lithium ferrite from 4.2°K to room temperature and at several microwave frequencies. Our purpose was to compare the linewidth characteristics of ordered lithium ferrite with those of YIG in the low‐temperature range. We find that nominally pure lithium ferrite exhibits a small linewidth peak at about 19°K as compared to roughly 40° to 50°K for YIG. Of particular interest is the fact that in lithium ferrite the linewidth increases with microwave frequency both below and above the linewidth peak and that the peak occurs at the same temperature independent of microwave frequency. For YIG below the peak, the linewidth decreases with increasing microwave frequency. In an attempt to determine the origin of the linewidth peak in lithium ferrite, several samples were made with small dopings of silicon and manganese. These samples also had a linewidth peak at 19°K, but the height of the peak was roughly the same for undoped and doped samples made at the same time. Chemical analysis and conductivity measurements showed that the pure samples did not contain significant amounts of Fe⁺⁺ or manganese, that the silicon‐doped samples contained Fe⁺⁺, and that manganese probably enters the lithium ferrite lattice as Mn³⁺. Apparently, neither Fe⁺⁺ nor Mn³⁺ is the primary cause of the linewidth peak in lithium ferrite. Also, calcium‐doped YIG, which is known to contain Fe⁴⁺, did not show a linewidth peak. It appears that the linewidth peak in lithium ferrite is not due to an impurity ion.