Gd+ ions were implanted at total doses of 3-6x10(14) cm(2) into single-crystal GaN or AlN epilayers grown on sapphire substrates and annealed at 700-1000 degrees C. The implanted Gd showed no detectable diffusion in either material after annealing, as measured by secondary ion mass spectrometry, corresponding to a diffusion coefficient < 8x10(-12) cm(2) s(-1). Under all annealing conditions, x-ray diffraction shows the formation of second phases. In the case of GaN, these include Gd3Ga2, GdN, and Gd, while for AlN only Gd peaks are observed. Both the GaN and AlN show high saturation magnetization after annealing at 900 degrees C (similar to 15 emu cm(-3) for GaN and similar to 35 emu cm(-3) for AlN). The magnetization versus temperature characteristics of the Gd-implanted GaN show a blocking behavior consistent with the presence of precipitates, whereas the AlN shows a clear difference in field-cooled and zero-field-cooled magnetization to above room temperature which may also be due to Gd inclusions. (c) 2006 American Institute of Physics