Eur. Phys. J. Special Topics 224, 1041–1060 (2015)
https://doi.org/10.1140/epjst/e2015-02445-4

Review

Spin dynamics and spin freezing at ferromagnetic quantum phase transitions

¹ Physik-Department, Technische Universität München, 85748 Garching, Germany
² Heinz Maier-Leibnitz Zentrum, Technische Universität München, 85748 Garching, Germany
³ Max-Planck-Institute for Chemical Physics of Solids, 01187 Dresden, Germany
⁴ Department of Physics, Royal Holloway, University of London, Egham TW20 0EX, UK
⁵ Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK
⁶ Departments of Physics and Chemistry, Princeton University, Princeton, NJ 08544, USA
⁷ Röntgenzentrum, Technische Universität Wien, 1060 Vienna, Austria
⁸ RWTH Aachen, Institut für Kristallographie and Forschungszentrum Jülich GmbH, JCNS at Heinz Maier-Leibnitz Zentrum, 85748 Garching, Germany
⁹ Institute of Condensed Matter Physics, Technische Universität Braunschweig, 38106 Braunschweig, Germany

^a e-mail: christian.pfleiderer@frm2.tum.de

Received: 1 March 2015
Revised: 15 May 2015
Published online: 22 July 2015

Abstract

We report selected experimental results on the spin dynamics and spin freezing at ferromagnetic quantum phase transitions to illustrate some of the most prominent escape routes by which ferromagnetic quantum criticality is avoided in real materials. In the transition metal Heusler compound Fe₂TiSn we observe evidence for incipient ferromagnetic quantum criticality. High pressure studies in MnSi reveal empirical evidence for a topological non-Fermi liquid state without quantum criticality. Single crystals of the hexagonal Laves phase compound Nb_1−yFe_2+y provide evidence of a ferromagnetic to spin density wave transition as a function of slight compositional changes. Last but not least, neutron depolarisation imaging in CePd_1−xRh_x underscore evidence taken from the bulk properties of the formation of a Kondo cluster glass.