Super space application on magnetic structures analysis

Orateur : Dr. Fabio ORLANDI (Università di Parma - Dipartimento di Chimica – Italy)

The super space approach is the standard method to solve and analyse commensurate and incommensurate nuclear modulated structures. However, modulation can be observed in magnetic structures as well and the application of super space to these cases, proposed at the early stage of its development by Janner and Janssen [1], has been described in few published works. This formalism is based on the knowledge of the magnetic point groups (Shubnikov groups) and to the introduction of additional dimensions to define incommensurate periodical distortions of spin arrangements throughout the magnetic lattice [2,3]. The refinement of selected parameters related to the magnetic symmetry expressed in a n-dimensional space efficiently determines the solution of the magnetic modulation. On the other hand the knowledge of the magnetic super-space group supports the analysis of the physical features of the system and it assumes particularly significance in the case of multiferroic materials where the spin-lattice coupling plays an essential role. In this seminary a brief introduction to the super space formalism and its application to the magnetic structure analysis will be given. Moreover an example of its application to the multiferroic Pb2MnWO6 double perovskite will be illustrate. This system presents a complex magnetic structure with propagation vector k=(¼00) and shows a particular thermal evolution of the magnetic modulation.

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