Incommensurate magnetism near quantum criticality in CeNiAsO

CeNiAsO is isotructural to the 1111 Fe-based superconductors but exhibits Rare-earth based heavy fermion magnetism. Two phase transitions in the tetragonal strongly correlated electron system CeNiAsO were probed by neutron scattering and zero field muon spin rotation ( μSR) [1]. For T < T_N1 = 8.7(3) K, a second order phase transition yields an incommensurate spin density wave with wave vector k = (0.44(4), 0, 0). For T < T_N2 = 7.6(3) K, we find co-planar commensurate order with a moment of 0.37(5) μB. By substitution of P for As or by applying pressure, the material can be driven into a paramagnetic Fermi-liquid phase [2]. Non-Fermi-liquid transport is found up to the critical phosphorus concentration xc = 0.4(1). We employed μSR to study several compositions across the phase diagram. CeNiAs1−xPxO shows the commensurate order only exists for x ≤ 0.1 so the transition at xc = 0.4(1) is from an incommensurate longitudinal spin density wave to a paramagnetic Fermi liquid. Within the conventional Hertz-Millis framework this suggests the volume of the Fermi-surface is sustained through the Quantum critical point and yet the anomalous transport properties are incompatible with this framework.
[1] Shan Wu, et al. arXiv:1707.09645 (2017)
[2] Luo, Y. et al. Nature Material 13,777-781(2014)