Cation intermixing and ordering phenomenon in M–O layer of MSr2YCu2Oz (M-1212) compounds with M=Fe, Co, Al, and Ga: A neutron powder diffraction study

Abstract

Various MSr2YCu2Oz (M-1212 with M=Fe, Co, Al, and Ga) compounds have been synthesized through a solid-state reaction route. All these compounds are derived from the basic CuBa2YCu2O7−δ structure. Rietveld structural refinement of the room-temperature neutron diffraction data for Fe-1212 reveals that nearly half of Fe remains at the M site, while the other half goes to the Cu site in the CuO2 plane. For the M=Co, Al, and Ga compounds, the basic unit cell gets doubled due to two distinct M sites in the M–O layer and the space group Ima2, without any cation intermixing is found to be more appropriate. For the M=Fe sample, magnetic ordering of Fe spins is seen from magnetization data below 70 K. In the case of the M=Co compound, a shallow down-turn in magnetic susceptibility is seen below 150 K, indicating low-dimensional magnetic characteristics of the Co–O layer. The compounds with M=Al and Ga show paramagnetic behavior in their magnetization data down to 5 K. The oxygen content, established for each compound based on oxygen occupancies, refined from the neutron diffraction data comes close to 7.0 for each.