Spontaneous partitioning of the Ni + C60 thin film grown at RT

We report on the pattern formation in the thin film of the Ni + C60 mixture deposited on the MgO(0 0 1) substrate at room temperature (RT). Using magnetic force microscopy a periodic array of the magnetic domains has been revealed. The domains reflect hidden partitioning of the Ni + C60 film (i.e., separated Ni- and C60-rich zones) that has not been observed by other applied methods. The effect indicates that even at RT, spontaneous separation of the Ni and C60 phases may set in during the growth of the hybrid film. Thermal annealing (for 1 h at 500 °C) leads to dramatic rearrangement of the Ni + C60 structure which (consequently) also results in the loss of the magnetic domain system. This phenomenon points out the thermodynamic instability of the as-prepared hybrid film that can (at elevated temperatures) trigger the process of the Ni and C60 phase separation.