Local structural correlations in the crystalline and glassy phases of Mn3Al2Si3O12

The compound Mn3Al2Si3O12 has two structural forms: the crystalline garnet spessartine which is a naturally occurring mineral, and a structural glass form. Both forms are magnetic due to the Mn2+ ions which have spin-5/2. In spessartine the Mn ions are 4+4-fold coordinated by Oxygen and are arranged as a highly frustrated network of corner-sharing triangles eventually developing long-range antiferromagnetic order at low temperatures. In the glass the coordination and arrangement of the Mn ions is unknown, however stronger antiferromagnetic interactions are present as revealed by a large negative Curie-Weiss temperature (4.5 times stronger than in spessartine). The goal of this experiment is to perform a total scattering measurement using GEM at room temperature of both forms of Mn3Al2Si3O12 in order to learn (1) to what extent the local structural correlations are different in the glassy and crystalline phases (2) the structural origin behind the development of the glass phase, (3) the immediate environment (coordination bond lengths and angles) of the cations in the glass compared to the crystalline phase and (4) their role in the contrasting magnetic properties of these two phases.