The magnetic order in YCa2[SbFe](Fe3)O12 is very complex and field-dependent due to the substitution of diamagnetic Sb5+ ions on the octahedral sublattice. The magnetic behavior differs from that observed in Y2Ca[ZrFe](Fe3)O12 presumably due to charge differences on the substituted cations. The main ferrimagnetic transition due to a-d coupling of the octahedral and tetrahedral sites is very broad and extends down to ca. 140 K. Below this temperature, the antiferromagnetic d-d exchange on the tetrahedral sites becomes significant and is thought to cause canting of the tetrahedral moments. At 10 K, the moments at both octahedral and tetrahedral sites determined by powder neutron diffraction-2.2(2) and 1.5(1) μB respectively—are very low and are consistent with significant canting on both cation sublattices. Mössbauer spectroscopy revealed five nonequivalent tetrahedral sites which relate to the occupation of nearest neighbor octahedral sites by a statistical distribution of Sb5+ and Fe3+ ions. © 1995 Academic Press. All rights reserved.