The magnetic and structural properties of the layered manganite ${\mathrm{Sr}}_7{\mathrm{Mn}}_4{\mathrm{O}}_{15}$ have been studied by powder neutron diffraction and magnetic susceptibility techniques between 5 and 300 K. The structure consists of pairs of face sharing ${\mathrm{MnO}}_6$ octahedra to form ${\mathrm{Mn}}_2{\mathrm{O}}_9$ dimers. The description of the crystal structure has been improved by employing a model in which some of the Sr and O ions are statistically distributed over two different sites. Three different magnetic phases can be distinguished in the temperature region studied. Below ∼75 K, the ${\mathrm{Mn}}^{4+}$ sublattice is antiferromagnetically ordered with an antiparallel alignment between all nearest-neighbor manganese ions. Between ∼75 and ∼150 K extensive quasi two-dimensional magnetic clusters are present. At temperatures above ∼150 K, one can observe correlations related to intradimer spin pairing. Truly paramagnetic behavior is not observed at any temperature below 300 K.

• Received 15 December 2000

DOI:https://doi.org/10.1103/PhysRevB.64.214403