Ferromagnetic resonance linewidth mechanisms in polycrystalline ferrites: Role of grain-to-grain and grain-boundary two-magnon scattering processes

Abstract

The frequency dependence of the ferromagnetic resonance linewidth ⌬H in polycrystalline hot isostatically pressed pure and CaGe substituted yttrium iron garnet ͑YIG͒ spheres was measured between 1.95 and 6 GHz and analyzed. The linewidths for these ultradense ferrite materials are in the 5-40 and 5-25 Oe ranges for the pure and the substituted YIG samples, respectively. The ⌬H vs frequency data show especially sharp Buffler peaks due to the band-edge crossover effect that is the signature for grain-to-grain ͑GG͒ two-magnon scattering ͑TMS͒ ͓C. R. Buffler, J. Appl. Phys. 30, S172 ͑1959͔͒. Both the GG and recent grain-boundary ͑GB͒ TMS models were used to obtain quantitative fits to the data. The fits demonstrate the expected GG TMS contribution to the linewidth for frequencies above the Buffler peak. They also reveal two unexpected results: ͑1͒ a dominant GB TMS role for frequencies below the Buffler peak where the GG TMS linewidth contribution is essentially zero and ͑2͒ a significant GB TMS role for frequencies above the peak where the linewidth has generally been associated with GG processes only. In the high-frequency regime, the GB scattering term appears to explain about half of the overall linewidth.

Effects of domain, grain, and magnetic anisotropy distributions on magnetic permeability: Monte-Carlo approach

“…Additionally, it is well known that there are many mechanisms for inhomogeneous broadening of linewidth of polycrystalline ferrites, such as porosity, anisotropy, and grain boundary and grain-to-grain magnon scattering processes. [32][33][34] Experimentally, high quality polycrystalline imaginary parts of the diagonal permeability for measured and calculated demagnetized YIG where domain demagnetization factor was fixed and grain demagnetization factor was varied. Numbers correspond to the simulations listed in Table I.…”

“…YIG linewidths vary from $5 to 45 Oe depending on frequency, 34 whereas single crystal YIG linewidth at 10 GHz is $0.5 Oe. 33 If the damping parameter a is calculated from experimental linewidths of polycrystalline ferrites, very large damping parameters are obtained, $0.05 to 0.45 (for H a ¼ 50 Oe, g ¼ 1.97, and DH ¼ 5 or 45 Oe).…”

“…From a physical standpoint, the frequency dependence of the linewidth is due to various processes such as grain-to-grain and grain-boundary magnon scattering. 34 To further compare the effect of distribution with the change in the damping parameter a, we explored the best fit of demagnetized YIG (beta A for both domains and grains) by setting the damping parameter a ¼ 0.0006, 0.006, 0.06, and 0.6. These choices contain the range of values seen in the literature from the experimental value to approximately that used for fitting other ferrite data.…”

Effects of interactions on the relaxation processes in magnetic nanostructures

“…The resulting dynamics can then be analyzed to determine effective parameters governing the relaxation process. This technique has been applied to a wide range of materials and structures [7][8][9][10]. In particular optical FMR is the preferred method for measuring the damping and resonance frequencies in materials with a strong magnetocrystalline anisotropy [11], due to the high fields required to drive the system to resonance in a typical ferromagnetic resonance experiment [12].…”

M-Type Barium Hexagonal Ferrite Films

“…The fact that the absorption is lower and the bandwidth is larger at low fields may be a result of low-field loss effects. 53 …”