Electronic phase transitions and magnetoresistance in a new bilayer manganate, Ca2.5Sr0.5GaMn2O8

The crystal structure of the anion-deficient perovskite Ca2.5Sr0.5GaMn2O8 has been studied at 290 and 5 K by neutron diffraction (290 K; space group Pcm2(1), a = 5,4294(l), b = 11.3722(3), c = 5.2983(1) Angstrom). The vacant oxide sites order to create a structure in which perovskite bilayers consisting of MnO6 octahedra are isolated from each other along [010] by a single layer of GaO4 tetrahedra. At 5 K the material is antiferromagnetic with an ordered magnetic moment of 3.09(1) mu(B) per Mn cation. Magnetic susceptibility measurements suggest that short-range magnetic ordering within the bilayers occurs above 200 K, and muon spin relaxation data show that the transition to long-range magnetic order occurs between 150 and 125 K. The resistivity of Ca2.5Sr0.5GaMn2O8 decreases by an order of magnitude at 125 K, and similar to50% magnetoresistance is seen in a field of 80 kOe at 110 K.