FERROMAGNETIC-RESONANCE OF SPHERICAL-PARTICLES OF ALPHA-IRON PRECIPITATED IN FUSED-SILICA

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 K 1, 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.