Incommensurate Magnetism Near Quantum Criticality in CeNiAsO.

Abstract

We report the discovery of incommensurate magnetism near quantum criticality in CeNiAsO through neutron scattering and zero field muon spin rotation. For T<T_{N1}=8.7(3) K, a second order phase transition yields an incommensurate spin density with a wave vector k=(0.44(4),0,0). For T<T_{N2}=7.6(3) K, we find coplanar commensurate order with a moment of 0.37(5)μ_{B}, reduced to 30% of the saturation moment of the |±1/2⟩ Kramers doublet ground state, which we establish through inelastic neutron scattering. Muon spin rotation in CeNiAs_{1-x}P_{x}O shows the commensurate order only exists for x≤0.1 so we infer the transition at x_{c}=0.4(1) is between an incommensurate longitudinal spin density wave and a paramagnetic Fermi liquid.