Ferromagnetic Resonance and Spin Diffusion in Supermalloy

Measurements of the shape of the ferromagnetic resonance line at 9.17 GHz have been made in Supermalloy at 25°C as a function of the angle between the applied static magnetic field and the normal to the sample surface. Comparison with theory indicates that the damping is dominated by spin diffusion with effective pinning of the surface spins. A saturation induction $4\pi M=7970\mathrm{}$ G and a spectroscopic splitting factor $g=2.093\mathrm{}$ are found for the combination of diffusion damping with the effects expected from an assumed exchange stiffness $A={10}^{-6\mathrm{}}$ erg/cm and a bulk resistivity $\rho =65\mathrm{}$ μΩ cm. The required diffusion constant $D=0.064\mathrm{}$ ${\mathrm{cm}}^2$/sec is larger than that which can be reasonably attributed to a single conduction band of $d$ electrons, but it is not too large to be explained by the combined systems of $d$ and $s$ electrons in which the $d$ electrons carry most of the magnetization, the $s$ electrons carry most of the conduction current, and an exchange coupling of a reasonable order of magnitude exists between them. The required magnitudes of parameters are $J_{\mathrm{sd}}=0.106\mathrm{}$ eV for the exchange interaction between $s$ and $d$ electrons, and $m_s^{}{}_{}{}^{*}=1.3\mathrm{}{m}_e$ and $v_s={10}^8$ cm/sec for the effective mass and Fermi velocity of the $s$ electrons.