Fe and N ions were co-implanted into Si wafers using the metal vapor vacuum arc technique and Kaufman technique. Structural analysis showed that Fe ions existed in the matrix at isolated substitution sites in the low dose sample (2.0 x 10(16) cm(-2)), while in the high dose samples of 5.0 x 10(16) cm(-2) and 2.0 x 10(17) cm(-2), the non-ferromagnetic FeSi2 phase formed. The co-implanted samples with the high implanted doses of 5.0 x 10(16) cm(-2) and 2.0 x 10(17)cm(-2) showed room-temperature ferromagnetism. The saturated magnetization decreased with the increase of the implanted dose. Self-annealing can make for the formation of FeSi2 phase, which resulted in the observed decrease in the saturated magnetization. The origin of the ferromagnetism was from the substituted Fe ions randomly embedded in the Si matrix. (c) 2011 Elsevier B.V. All rights reserved.