Detection of picosecond magnetization dynamics of 50 nm magnetic dots   down to the single dot regime
  We report an all-optical time-domain detection of picosecond magnetization dynamics of arrays of 50 nm Ni80Fe20 (permalloy) dots down to the single nanodot regime. In the single nanodot regime the dynamics reveals one dominant resonant mode corresponding to the edge mode of the 50 nm dot with slightly higher damping than that of the unpatterned thin film. With the increase in areal density of the array both the precession frequency and damping increases significantly due to the increase in magnetostatic interactions between the nanodots and a mode splitting and sudden jump in apparent damping are observed at an edge-to-edge separation of 50 nm. 
Bivas Rana, Dheeraj Kumar, Saswati Barman, Semanti Pal, Yasuhiro   Fukuma, YoshiChika Otani, and Anjan Barman
cond-mat.mes-hall cond-mat.mtrl-sci