Ferromagnetic Resonance and Nonlinear Effects in Ferrites with Uniaxial Anisotropy

Abstract

A study of the ferromagnetic resonance properties in single crystal Zn2+–Ti4+ substituted barium ferrite (BaZnxTixFe12–2xO19) with uniaxial anisotropy has been performed over the frequency range 23.2–37.6 GHz. By varying the amount of zinc and titanium substitution, the anisotropy field can be varied from 17 000 to 5000 Oe. This investigation concentrated on the composition in which x=2.25. These samples had an anisotropy field of 6590 Oe and a saturation magnetization of 2300 G. Cavity perturbation techniques were used with polished spherical samples 15–20 mils in diameter. The measured resonance linewidth along the easy axis was 43.2 Oe at 23.2 GHz and increased to 82.5 Oe at 37.6 GHz. Extrapolation of resonance data gave γ=2.75 MHz/Oe. As the incident rf power was increased at 36.1 GHz, nonlinear effects were observed. The threshold field for spin wave excitation was 0.86 Oe. Using an extension of nonlinear spin-wave theory to include uniaxial anisotropy, an intrinsic spin-wave linewidth of 0.97 Oe was calculated.