CRYSTAL AND MAGNETIC-STRUCTURES OF CA4MN3O10, AN N=3 RUDDLESDEN-POPPER COMPOUND

The crystal and magnetic structures of the n = 3 Ruddlesden-Popper pha se with the ideal composition Ca4Mn3O10 have been studied using X-ray and neutron powder diffraction. The crystal structure at 293 K is rela tively insensitive to the partial pressure of oxygen used in sample pr eparation. A sample prepared in air showed an orthorhombic distortion (space group Pbca, a = 5.26557(12), b = 5.26039(11), c = 26.8276(5) An gstrom) from the ideal n = 3 RP structure, as did a sample prepared un der 800 atm of O-2 pressure (a = 5.26005(4), b = 5.25569(4), c = 26.83 543(20) Angstrom). Both samples showed a magnetic phase transition at 115 K from a paramagnetic phase with extensive short-range spin orderi ng to a weakly ferromagnetic (mu(ferro) = 2 x 10(-3) mu(B) per Mn) low -temperature phase. The antiferromagnetic components of the atomic mag netic moments (2.23(2) mu(B) per Mn) order in a G-type manner within e ach perovskite block, and the interblock coupling reflects the orthorh ombic symmetry of the structure.