Spin dynamics and spin freezing at ferromagnetic quantum phase transitions

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 Nb1−y Fe2+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 CePd1−x Rh x underscore evidence taken from the bulk properties of the formation of a Kondo cluster glass.