Determination of the exchange stiffness in ultrathin magnetic films by magnonic patterning and ferromagnetic resonance

In ultrathin films of below 20 nm thickness, it is hardly possible to determine the exchange constant A, since perpendicular standing spin waves (PSSWs) are shifted up to inaccessibly high energies. In this work, a method is presented to analytically determine the exchange stiffness constant D = 2A/MS using ferromagnetic resonance (FMR) and magnonic patterning. Usual FMR measurements, however, are not influenced by the value of D, since no exchange energy is involved in uniform precession. To overcome this problem a coupling mechanism, such as two-magnon scattering (TMS), can be employed to couple exchange dominated in-plane spin waves with the uniform mode.
In our approach lateral magnetic surface patterning was carried out to artificially induce TMS. Subsequent FMR measurements give access to the spin wave spectra of backward volume modes, and thus, to the exchange stiffness constant D.