GaMn icosahedral particles with quasicrystalline order have been found in Mn implanted and rapidly annealed GaAs by means of selected-area electron diffraction, high-resolution, and dark-field electron microscopy. The orientation relationship between the submicron quasicrystals with the icosahedral(2/m 3¯5¯)symmetry and the face-centered cubic (fcc) GaAs matrix is determined to be:i5¯(the fivefold inversion axis in(2/m 3¯5¯))//[110]GaAs,i3¯(the threefold inversion axis)//[111¯]GaAs,andi2(the twofold axis)//[121¯]GaAs.The statistics of these structural studies, combined with magnetic force microscopy, indicate that the submicron quasicrystals are ferromagnetic. ©1997 American Institute of Physics.