Magnetoelastic paradox: Absence of symmetry-breaking distortions below in antiferromagnetic systems without orbital momentM. Rotter1, A. Lindbaum1, A. Barcza1, M. El Massalami2, M. Doerr3, M. Loewenhaupt3, H. Michor4 and B. Beuneu5
1 Institut für Physikalische Chemie, Universität Wien - Währingerstr. 42, Austria
2 Instituto de Fisica, UFRJ - Caixa Postal 68528, 21945-970, Rio de Janeiro, Brazil
3 Institut für Festkörperphysik, Technische Universität Dresden 01069-Dresden, Germany
4 Institut für Festkörperphysik, Technische Universität Wien - 1040-Wien, Austria
5 Laboratoire Léon Brillouin, CEA-CNRS Saclay - 91191 Gif-sur-Yvette Cedex, France
received 24 February 2006; accepted in final form 12 May 2006
published online 2 June 2006
Phase transitions are often associated with symmetry breaking. In case of magnetic order time reversal symmetry is broken and this leads to magnetostriction. For magnetic systems without orbital moment (L=0) the only source of magnetostriction is believed to be the exchange striction (ES). If the systems, for instance -based compounds (S=7/2, L=0), order ferromagnetically (fm) no lattice distortions are expected from the standard model of rare-earth magnetism, whereas in the antiferromagnetically (afm) ordered compounds symmetry-breaking lattice distortions should occur. These latter prediction of the theory is in complete contrast to all available experimental data on antiferromagnets. They show in many cases large magnetostrictive effects, but no symmetry breaking. Thus we can formulate the "magnetoelastic paradox": in afm systems without orbital moment (L=0) symmetry-breaking distortions below the Néel temperature are expected, but have not been found. New experimental data indicates, that the magnetoelastic paradox is only present in zero field and may be lifted by a small magnetic field.
75.80.+q - Magnetomechanical and magnetoelectric effects, magnetostriction.
© EDP Sciences 2006