Frequency and temperature dependence of the ferromagnetic resonance linewidth in single crystal platelets and pulsed laser deposited films of barium ferrite

Abstract

The half power ferromagnetic resonance (FMR) linewidth ΔH has been measured from 8 to 300 K for a nominal frequency of 61 GHz and from 50 to 75 GHz at room temperature for normally magnetized single crystal platelets and pulsed laser deposited (PLD) films of barium ferrite. The platelet linewidth versus temperature data show a peak value of 27 Oe at 25–30 K, a dip to 21 Oe at 75 K, structure related to line merging at 130–160 K, and a region of slow increase at 240–295 K. The 240 –300 K data extrapolate to a 0 K linewidth of about 8 Oe. The corresponding film data show a peak value of 240 Oe at 20 K and a gradual decrease at higher temperatures. Both the platelet and film linewidths show a weak frequency dependence at about 0.3 Oe/GHz at room temperature (RT). The film data also show several linewidth spikes due to interference effects between the FMR response and dielectric resonances in the substrate. The RT linewidth zero frequency intercepts for the platelet and the film were 9 and 30 Oe, respectively. The frequency dependence of the platelet linewidth was also examined at 230–295 K. The frequency responses and intercepts for these data were affected by the line merging at lower temperatures and showed high temperature limit values of 0.35 Oe/GHz and 9.5 Oe, respectively. The linewidth frequency response in both cases is attributed to conductivity. The linewidth versus temperature peaks are attributed to impurities. The linewidth dip at 75 K for the platelet results from the drop in ΔH on the tail of the temperature peak and an increase associated with iron ion hopping motion.