Study of spin transfer torque in serially connected pillars by means of ferromagnetic resonance

We investigate the influence of the spin polarized current on magnetic damping in the ferromagnetic layers of pillar structures by means of ferromagnetic resonance (FMR). The pillars are prepared and electrically contacted by high-resolution electron beam lithography and electron beam evaporation in a multi-step process. FMR measurements are carried out on a pillar array, in which all pillars are connected in series, so that the current density reaches values high enough to observe the effect of the spin transfer torque on the FMR signal. The temperature rise due to the high current density is avoided by cooling. An influence of the spin transfer torque effect on the intrinsic damping in the ferromagnet is observed. The fabrication of the serial connection can be easily applied to arbitrary structures.