Computational and Experimental Studies of Magnetism in Melilites

Abstract

The melilite class of materials offers many avenues for research into magnetic interactions. The melilite crystal structure has the chemical formula A2BC2D7 and can accommodate many different elements on the A-, B-, C- and D-sites. For compounds with magnetic transition metal atoms on the B-site, the layered nature of the material produces a nearly two dimensional magnetic sub-lattice. Also, due to the non-centrosymmetric space group which is found in several versions of this structure, multiferroic ordering and magnetoelectric coupling can be observed. Our literature review of the melilite class of materials shows that while there is detailed information available for several magnetic melilite compounds, the magnetic properties of most magnetic melilites have not been studied. Ab initio theoretical calculations of the 1-2-5-2 and 2-2-4-2 manganese melilites and other related materials confirmed the stability of the melilite phase and identified a predominant G-type magnetic ordering. However, several melilite materials including Ba2MnSi2O7 were predicted to have a C-type ordering. Theoretical and experimental studies concerning structural and magnetic properties were performed on K2CoP2O7 twisted melilite and Ba2MnSi2O7 melilite materials which confirmed our theoretical modelling. Further studies outside of the melilite family of materials using similar methodologies were also performed on ZrMn2-xCoxGe4O12 and glaserite Ba3MnSi2O8. However, this thesis mainly focuses on the melilite family of materials as these offer a large scope for further research.