Spin dynamics and spin freezing at ferromagnetic quantum phase transitions

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An increasing number of experimental and theoretical studies suggest that quantum criticality of itinerant-electron ferromagnets, quite generally, does not exist in real materials. This raises the question what mechanisms pre-empt ferromagnetic quantum criticality. In the simplest scenario the single-particle density of states or certain many body interactions drive the quantum phase transition first order. Further possibilities include the emergence of ordered phases such as superconductivity or partial electronic order, e.g., nematic electronic phases. Finally, the emergence of long-range modulations and electronic phase separations may be expected that are driven by weak residual interactions. We propose to search for electronic phase separations near ferromagnetic quantum criticality in a wide range of transition metal and rare earth compounds using neutron depolarization radiography and neutron depolarization tomography; these are new neutron scattering techniques we developed during the first funding period. Our studies will be complemented by conventional inelastic neutron scattering studies and comprehensive measurements of the bulk properties.