THE MAGNETIC-PROPERTIES OF BALACOIRO6 AND BA3COIRXRU2-XO9

The magnetic structure of the antiferromagnetic phase of the pseudo-cu bic perovskite BaLaCoIrO6 has been determined from time-of-flight powd er neutron diffraction data collected at a temperature of 4 K. The Co( II) cations adopt a Type II collinear spin structure with an ordered m oment of 2.8(2) mu(B) per Co(II); the Ir(V) cations do not have a dete ctable ordered magnetic moment. Magnetic susceptibility measurements o n the compounds Ba3CoIrxRu2-xO9 (0<x less than or equal to 2) resulted in the observation of weak ferromagnetism; the saturation magnetizati on decreased with increasing Ru content. Comparisons are made between BaLaCoIrO6 and the spin glass BaLaCoRuO6, and also between Ba3CoIr2O9 and antiferromagnetic Ba3CoRu2O9. The behaviour of the nominally non-m agnetic Ir(V) cations is discussed and contrasted with that of diamagn etic Sb(V) in Ba3CoSb2O9 and Ba3CoIrSbO9.