Structural and Solid-State Examination of Ca4Mn3O10 and Sr4Mn3O10

A comparative study of the manganates Ca4Mn3O10 and Sr4Mn3O10 shows them to belong to distinct structural classes, of Ruddlesden-Popper and Cs4Ni3F10 type respectively. Our determinations show both compounds to be orthorhombic, with Ca4Mn3O10 in space group Ccc2, with a = 5.240, b = 26.823, c = 5.276 Ǻ, and Sr4Mn3O10 in space group P2221, with the cell dimensions of a = 5.481(1), b = 6.237(1), c = 12.528(2) Ǻ. In addition, Ca4Mn3O10 is found to undergo a transition at 122 K, below which temperature there is evidence for antiferromagnetic ordering and for a sharp conductor-to-insulator transition. This appears to be a new form of giant magnetoresistance (GMR), differing from previous reports in that it occurs in an undoped , layered bulk perovskite.