Ferri- and ferro-magnetism in CaMnMReO6 double double perovskites of late transition metals M = Co and Ni.

Two new double double perovskites of ideal compositions CaMnMReO6 (M = Co, Ni) are reported. The M = Co material has refined composition CaMn0.7Co1.3ReO6 and orders ferrimagnetically below TC = 188 K with a relatively large saturated magnetisation of 4.5 μB. The M = Ni product, CaMn1.2Ni0.8ReO6, is a remarkable example of a ferromagnetic oxide with four distinct spin sublattices all collinearly ordered below TC = 152 K.