Regensburg 2013 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe

MA: Fachverband Magnetismus

MA 45: Magnetic Coupling and Spin Structures

MA 45.9: Vortrag

Donnerstag, 14. März 2013, 17:15–17:30, H10

Slow magnetic order-order transition in antiferromagnet Ca₃Co₂O₆ — •Stefano Agrestini¹, Martin Lees², Catherine Fleck², Laurent Chapon³, and Claudio Mazzoli⁴ — ¹Max Planck Institut für Chemische Physik fester Stoffe, Dresden, Germany — ²Physics Department, University of Warwick, Coventry, UK — ³ILL, Grenoble, France — ⁴Politecnico di Milano, Milano, Italia

Time-dependent phenomena play a crucial role in the properties of many magnetic systems, including spin-glasses, single-molecule magnets and superparamagnets. However time-dependent magnetism is not expected to be observed in the presence of long-range magnetic order. Here we challenge this view by reporting the observation of a new time-dependent behavior where a transition from one long-range magnetically ordered state to another occurs in zero magnetic field over a time scale of several hours. We performed an extensive neutron diffraction study of the spin chain system Ca₃Co₂O₆ whose step-like magnetization versus magnetic field aroused great interest in the scientific community. Our data show that for T< 14K< T_N =25K the spin-density-wave order observed immediately below T_N, becomes unstable and a commensurate antiferromagnetic phase appears via a very slow transformation process. As the temperature is reduced the characteristic time of the transition process increases rapidly and at low temperatures the magnetic states become frozen. The transition is also noteworthy because the two phases have different propagation vectors. Very rarely transitions between two magnetically ordered phases involve a change of translational symmetry.