Low energy spin fluctuations in a ferromagnetic spin system at a quantum critical point

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In this project we propose to investigate the electronic ground state and spin dynamics of the correlated electron system RNi4X2 (R: Yb, Lu, X: P, As) by means of Nuclear Magnetic Resonance (NMR) and Muon Spin Relaxation (μSR) studies. YbNi4P2 is a newly discovered ferromagnetic (FM) Kondo lattice system with a very low FM ordering temperature. Therefore, this system is a new candidate for a model system showing ferromagnetic quantum criticality (FMQC). By substitution of As at the P site it is possible to tune the magnetism of this system and one can reach the quantum critical point. Our major goals are to determine the electronic phase diagram in the series YbNi4(P1-xAsx)2, examine static order parameters and the low frequency spin dynamics in the quantum critical regime and deduce the effective hybridization strength of the interaction between the 4f electrons and the conduction electrons from the hyperfine interactions in NMR and μSR experiments. In particular, we shall probe the magnetic field dependence of the critical fluctuations and/or the Kondo fluctuations from high fields towards zero external field.