Tuning magnetic exchange interactions in 'molecular orbital' material Sr7Mn4O15 by high pressure

The structure of Sr7Mn4O15 consists of face-sharing MnO6 octahedral dimers, which are potential candidates for formation of “orbital molecules”. The dimers form in strings in the ac-plane which in turn form layers in the a direction, leading to a strong anisotropy in exchange interaction. We have shown this phase to be extremely flexible to substitution by Ca2+ or Ba2+, leading to structural distortions and changes in the magnetic susceptibility. Counterintuitively, substitution by both smaller and larger cations on the Sr sites appear to reduce the ordering temperature of the phase. We aim to use PEARL to investigate the effect of high isotropic pressures on the various exchange pathways within the structure. Several pathways comprise Mn-O-Mn linkages, so neutron diffraction is an appropriate method for identifying positional distortions which may affect the exchange mechanism.