Dresden 2006 – scientific programme
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MA: Magnetismus
MA 20: Poster: Films(1-36) Transp(37-56) Ex.Bias(57-67) Spindyn(68-80) Micromag(81-95) Particle(96-109) Imag.+Surface(110-113) Spinelectr(114-122) Theory+Micromag(123-131) Spinstr+Aniso(132-142) MagMat(143-156) Meas(157,158) MolMag+Kondo(159-162) Postdead(163-)
MA 20.134: Poster
Tuesday, March 28, 2006, 15:15–19:15, P1
Relevant and non-relevant magnetic interactions — •Ulrich Köbler1, Andreas Hoser1,2, and Jens-Uwe Hoffmann3 — 1Institut für Festkörperforschung, Forschungszentrum Jülich, D-52425 Jülich — 2Institut für Kristallographie, RWTH-Aachen — 3Hahn-Meitner-Institut Berlin
Due to the atomistic lattice structure the length scale of the paramagnetic dynamics is limited by the finite near neighbour distance. On this length scale the strong short range Heisenberg interactions are the relevant interactions. Curiously, these interactions can best be investigated in the ordered state using inelastic neutron scattering. The observed excitation spectra are dominated by microscopic features such as lattice symmetry and magnetic structure. In contrast to the material specific excitation spectra the order parameter shows universality at the stable fixed points T=0 and T=Tc. Universality means independence of lattice symmetry and magnetic structure. This is a consequence of the large length scale of the dynamics for T → 0 and T → Tc . Continuum theories are therefore more appropriate than atomistic models. The discrepancy between the universality of the dynamics and the non universal magnetic excitations indicates that a new type of long range interaction becomes relevant in the ordered state. A further strong argument for this is the experimental observation that the dynamics is different for integer and half-integer spins in the ordered state but not in the paramagnetic phase. Dipole-dipole interaction is obviously not able to explain this difference.