The ordered arrangement of Cr^<3+> and Cr^<2+> ions, proposed by Steinfink and Burns, was confirmed by Osmond with application of the qualitative Goodenogh-Kanamori rules for superexchange interactions. This compounds should be antiferromagnetic, with equal numbers of ferromagneticallycoupled cations of both types in (011) planes and opposed spin directions in alternate planes. The magnetic behaviour of this antiferromagnetic crystal is discussed by the four sublatttice model.