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TT: Fachverband Tiefe Temperaturen

TT 31: Correlated Electrons: Other Materials

TT 31.1: Vortrag

Dienstag, 21. März 2017, 14:00–14:15, HSZ 103

Dipolar effects on the critical fluctuations in Fe: Investigation by MIEZE — •Steffen Säubert^1,2, Jonas Kindervater³, and Peter Böni¹ — ¹Physik Department, Technische Universität München, Garching, Germany — ²Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München, Garching, Germany — ³Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, USA

Iron is one of the archetypical ferromagnets to study the critical fluctuations at a continuous phase transition thus serving as a model system for the application of scaling theory. We report a comprehensive study of the critical dynamics at the transition from the ferro- to the paramagnetic phase in Fe, employing the high-resolution neutron spin echo technique MIEZE. The results show that the dipolar interactions lead to an additional damping of the critical spin fluctuations at small momentum transfers q. The results agree essentially with scaling theory if the dipolar interactions are taken into account by means of the mode-coupling equations. However, in contrast to expectations, the dipolar wavenumber q_D that plays a central role in the scaling function f (κ/q, q_D /κ) becomes temperature dependent. In the limit of small q the critical exponent z crosses over from 2.5 to 2.0.