Origin of magnetic phase transition in RMn2Si2 (R = rare-earth ion or Y) intermetallics

Abstract

The magnetic structures and magnetic phase transitions in intermetallic layered RMn2Si2 compounds (the ThCr2Si2-type structure) are investigated using the first-principles method. The type of ordering of Mn magnetic moments along the c-axis is found to be controlled by the distances between the Mn ions in the ab plane rather than the interplane distances, in agreement with experimental observations. To find the pathways that maintain the magnetic phase transition with alloying in RMn2Si2, we calculated the Heisenberg exchange interaction parameters for the Mn ions in YMn2Si2. We demonstrated that the Si ions form dimers and that the bonding molecular orbital of the dimer acts as a mediator of the indirect exchange (superexchange) interaction between the layers of the Mn ions along the c-axis. This superexchange interaction is the only antiferromargnetic one that stabilize the AFil structure along the c-axis and it is the driving force of the experimentally observed magnetic phase transition.