Relaxation Processes for Ferromagnetic Resonance in Thin Films

Abstract

Ferromagnetic-resonance linewidth measurements have been made for two hundred Ni–Fe alloy films (77% Ni) 150–3200 Å thick at frequencies from 1–9 Gc/sec with the static field in the film plane. To avoid dispersion effects samples with the smallest linewidth (ΔHmin) were selected for each thickness. For film thickness less than a frequency-dependent critical thickness Dω, ΔHmin is independent of film thickness. For thicker films where D > Dω, ΔHmin increases linearly with film thickness. The observed Dω values (about 1000 Å) are in good agreement with predictions based on magnon scattering involving spin waves degenerate with the uniform mode. Because of the magnetostatic mode modification of the spin-wave dispersion relation for thin films there are no spin-wave states degenerate with the uniform mode for D < Dω and magnon scattering is not allowed. The applicability of two different magnon processes, s-d exchange and two-magnon scattering, is discussed. Neither mechanism provides a completely satisfactory explanation of the data. The present data indicate: (1) For D > Dω, the linewidth is a linear function of film thickness and a magnon process is important. (2) For D < Dω, a magnon process is not important. (3) The anisotropy dispersion makes a contribution to ΔH, which is significant and may mask the above effects if the dispersion is large.

Two-magnon scattering in a self-assembled nanoscale network of misfit dislocations

“…18 -22 Patton and co-workers pioneered this concept in metallic films. 23 In this section we will summarize only those features of two-magnon scattering which are essential for the discussion of our results.…”

Nanosecond magnetic relaxation processes in ultrathin metallic films prepared by MBE

“…[3][4][5][6][7] The Patton group pioneered the use of two magnon scattering in metallic films. 8 In a wide range of metallic amorphous ribbons, 9 films, 10 and metallic ultrathin film multilayers 1,11,12 the ferromagnetic resonance ͑FMR͒ linewidth, ⌬H, above 10 GHz is not only proportional to the microwave angular frequency, , as expected from the Gilbert damping but possesses a zerofrequency offset ⌬H(0),…”

Increased Gilbert damping in spin valves and magnetic tunnel junctions

“…For Ni 80 Fe 20 , one of the most well-studied materials, the dispersion of a-values found in literature is large, e.g. a ¼ 0:00520:08: This dispersion is related to the sample quality [1], but also to the exact material system. Indeed, as for most material properties, the surface and interface damping can differ significantly from its bulk value.…”

“…We can determine the anisotropy field H K and the magnetization M eff from a set of fitted frequencies as a function of H DC : Our limited dataset allows no separate fit for g ¼ gm B m 0 =h and M eff , and we assumed g ¼ 2:21:10 5 m=As a constant. 1 The expression used to calculate the Gilbert damping from the fitted time decay rate t is a 0 ¼ 2=tgM s :…”