Very high coercive fields have been observed at low temperatures in an amorphous (Tb_0:27 Dy_0:73 )_0:32 Fe_0:68 sputter deposited thin film. Coercive field data are presented for films of different thickness. A very sharp decrease of the coercive field, similar to that in "bulk" amorphous REFe₂ (RE = rare earth), has been observed. The time effect on the remanent magnetisation has also been measured which is similar to that of superparamagnetic particles. The large values and the drastic temperature variation of the coercive field is very well explained by the partial breaking up of the long range magnetic order due to the presence of RE spins distributed randomly in the amorphous matrix.