Ferromagnetic resonance of spherical particles of α-iron precipitated in fused silica

Abstract

Ferromagnetic resonance (FMR) spectra were obtained at 9 and 35 GHz for particles of metallic iron precipitated in fused silica containing 1–120 ppm Fe. Accurate g values and anisotropy constants K₁, K₂ and K₃ were extracted by computer simulation of the powder pattern line shapes, assuming negligible shape anisotropy. One sample, melted under a He‐H₂O atmosphere, exhibited anisotropy constants identical with published values for pure α–iron and a g value of 2.081±0.002. Samples strongly reduced in H₂ displayed smaller values of K₁, consistent with expectation for alloying of the Fe with up to 20% Si. These K₁ values were shown to be statistically distributed and linearly correlated with the g values in the range 5?at.%Si?20. All samples displayed increases ∼ 5–10% in apparent K₁ value with increasing frequency, either as‐delivered or after aging. It is hypothesized that the latter effects are due to the formation of a magnetic iron oxide layer at the metal‐glass interface.