Ferromagnetic resonance in bulk nanocrystalline Ni

Abstract A detailed lineshape analysis of the ferromagnetic resonance (FMR) spectra taken on pulse electrodeposited nanocrystalline (nc-) Ni sheets (with the average crystallite size, d, varying from 10 nm to 40 nm) at temperatures ranging from 113 K to 325 K yield accurate values for saturation magnetization, M s (T), Lande splitting factor, g, anisotropy field, H k ( T ) , resonance field, H res , and FMR linewidth, Δ H pp ( T ) . Thermally-excited spin-wave (SW) excitations completely account for M s ( T ) and the SW description of M s ( T ) gives the values for the saturation magnetization and spin-wave stiffness at absolute zero of temperature, i.e., M s ( 0 ) and D 0 , for nc-Ni samples of different d that are in excellent agreement with the corresponding values deduced previously from an elaborate SW analysis of the bulk magnetization data. While M s ( 0 ) varies with d as M s ( 0 ) ~ d - 3 / 2 , D 0 follows the power law D 0 ∼ d 4 / 3 . The angular variations of H res in the ‘in-plane’ as well as ‘out-of-plane’ sample configurations, demonstrate that the main contribution to H k ( T ) comes from the cubic magnetocrystalline anisotropy. The exchange-conductivity mechanism describes the observed thermal decline of Δ H pp reasonably well but fails to explain the very large magnitude of Δ H pp at any given temperature. By comparison, the Landau-Lifshitz-Gilbert (LLG) damping gives a much greater contribution to Δ H pp but the LLG contribution is relatively insensitive to temperature.