Co2CrAl and Co2CrSi are amongst the most studied Heusler alloys due to their half-metallic character. These compounds are also well-known to present ferromagnetism with high Curie temperatures. We show using first-principles calculations that the creation of Cr antisites (Cr atoms at the Co sites) induces ferrimagnetism in these compounds without destroying the half-metallic character of these alloys. The reduction of the total spin moment causes lower external fields and thus smaller energy losses in realistic magnetoelectronic, also known as spintronic,devices. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.