Two magnon ferromagnetic resonance linewidths in uniaxial and planar single crystal hexagonal ferrites (abstract)

Hexagonal ferrites are ideally suited for millimeter-wave applications but have seen limited use because of large losses. High field effective linewidth and ferromagnetic resonance (FMR) linewidth measurements for single crystal barium ferrite indicate that these losses may be due to an inhomogeneity related two magnon scattering contribution to the relaxation. Calculations of the linewidth as a function of the external magnetic field orientation in films and thin disks give characteristic dependencies if two magnon scattering relaxation is present. The objective of this work was to measure the angle dependence of the FMR linewidth in single crystal Zn–Y and Ba–M hexagonal ferrite disks and compare the results to the theoretical predictions. The materials were flux grown Mn doped Ba–M and Zn–Y single crystals. The Ba–M and Zn–Y disks were 1.0 mm in diameter and 0.13 and 0.4 mm thick, respectively. Measurements were made at 53 GHz for the Ba–M and 9.5 GHz for the Zn2–Y. The FMR was measured by a shorted waveguide technique as a function of the field angle relative to the out-of-plane direction. The linewidth for the Ba–M increased from minimum value of 35 Oe at 0°, to a maximum of 330 Oe at 68°, followed by a small decrease out to the maximum angle of 75° for which FMR could be observed. For the Zn2–Y, the linewidth increased from 95 Oe at 0° to 420 Oe at 5°, followed by a decrease to 37 Oe at 90°. The two-magnon model gives large peaks in the linewidth as a function of angle, the sizes and positions of which depend upon the anisotropy and the size of the scattering inhomogeneities. The experimental results for both materials are in good agreement with model two-magnon calculations based on an inhomogeneity size on the order of 0.5 μm.