Magnetic properties of the (CoxMn1-x)4Nb2O9 solid solution series

α-Fe2O3 (Hematite) is an antiferromagnetic material below the Morin transition at 260 K, and a canted antiferromagnet or weakly ferromagnetic above the Morin transition and below its Neel temperature at 948 K, above which it is paramagnetic. (Co,Mn)4Nb2O9 crystallizes isostructural to α-Fe2O3 and the end members order collinear antiferromagnetically, whereas the results of magnetization measurements (powder samples and single crystals) and powder neutron diffraction experiments for samples of the solid solution series indicate the realization of weak ferromagnetism, too. A Morin transition induced by a change in cation composition in this system would have presented a qualitatively new approach for understanding the fundamentals of the Morin-transition. Comparative experiments performed on samples of the (Co,Mn)4Nb2O9 solid solution series that were prepared by arc melting instead of subsolidus reaction reveal, however, that the experiments performed on samples prepared by the latter method, even on single crystals, were decisively affected by additional (Co,Mn)3O4 phases possessing complex magnetic properties