Magnetization Relaxation in Sputtered Thin Fe Films: An FMR Study

Recently, various groups have proposed competing relaxation mechanisms on the magnetization damping in thin magnetic films. We used the ferromagnetic resonance (FMR) technique to understand this behavior from FMR linewidths of sputtered thin Fe films sandwiched by normal metals (NM=Cu, Al, Ti, and Ta) of 30 Aring on each side. We made samples of Fe(d)/GaAs(100), Al/Fe(d)/Al/GaAs(100), Cu/Fe(d)/Cu/GaAs(100), Ti/Fe(d)/Ti/GaAs(100), and Ta/Fe(d)/Ta/GaAs(100), with d=20 to 300 Aring. Delta H scales with d^-2 in bare Fe/GaAs and Al/Fe(d)/Al series of samples following the well-known two-magnon mechanism. The sandwich Fe series with Cu, Ti, and Ta follow d^-1 behavior attributed to recently proposed spin pumping process. After analyzing the data, we conclude Ti/Ta as good spin sink materials, with a mixing conductance twice/thrice larger than Cu. We termed Cu as poor spin sink material in the sandwich Fe structures. Our analysis shows that FMR linewidth data is a powerful tool to investigate interfacial transport properties of magnetic sandwich structures