El coloquio del viernes 15 de noviembre se titula "Magnetic Crystallography in Superspace". El expositor es Juan Rodriguez-Carvajal del Institut Laue-Langevin, Grenoble, Francia. Es profesor visitante del Programa Maldacena. Se realizará a las 14.30 hs. en el Salón de Actos del Instituto Balseiro, en el Centro Atómico Bariloche (Av. Bustillo 9500).La entrada es gratuita y abierta a todo el público. Para ingresar, es necesario presentar el DNI en la entrada del CAB.
In conventional Crystallography the symmetry properties of periodic arrangement of atoms are described by the 230 space group types in three dimensions. More complex spatial arrangements of atoms may need to be described by periodicity in higher dimensions. Under the term Magnetic Crystallography we group a special subfield of Crystallography concerned with the description and determination of the magnetisation density or, in quantum mechanical terms, the spin density in solids. The corresponding classical objects are axial vectors defining the elemental magnetic moments of the atoms. Contrary to crystal structures, many magnetic structures are non-commensurate: the periodicity of the orientation of the magnetic moments is not commensurate with the underlying crystal structure.
The symmetry properties of commensurate magnetic structures are currently described using two different approaches: the magnetic Shubnikov groups and the group representation analysis. For incommensurate magnetic structures the representation analysis can also be used but the most complete way of working with this class of magnetic structures is the use of the concepts of superspace crystallography, including now spin reversal as additional operator, to work with magnetic superspace groups. In this talk I will present a summary of this topic accompanied with examples.
Juan Rodríguez-Carvajal is doctor in Physics for the University of Barcelona. He has been the head of the Diffraction Group at ILL for 7 years. During his career he has worked on the fields of data analysis and software development in Crystallography and Diffraction, as well as on theoretical analysis of magnetic structures, frustration, and low dimensional magnetism. He is a leading scientist on applying neutron diffraction techniques to study structural and magnetic properties of oxides presenting metal-insulator transitions, superconductivity, colossal magnetoresistance, charge, spin and orbital ordering phenomena.