STRUCTURAL AND SOLID-STATE EXAMINATION OF CA4MN3O10 AND SR4MN3O10

A comparative study of the manganates Ca4Mn3O10 and Sr4Mn3O10 shows th em 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 Angstrom, and Sr4Mn3O10 in space group P222(1), with the cell dimensions of a = 5.481(1), b = 6.237(1), c = 12.528(2) Angstrom. In addition, Ca4Mn3O10 is found to undergo a transition at 1 22 K, below which temperature there is evidence for antiferromagnetic ordering and for a sharp conductor-to-insulator transition. This appea rs to be a new form of giant magnetoresistance (GMR), differing from p revious reports in that it occurs in an undoped, layered bulk perovski te.