Magnetic order and spin dynamics in the proximity of a ferromagnetic quantum critical point: A μSR study of YbNi4P2

The local 4f-electronic spin dynamics and magnetic order in YbNi4P2 were studied by means of muon-spin relaxation measurements. Zero-field muon-spin relaxation proves static magnetic order with a strongly reduced ordered Yb3+ moment of (2.5-4.6) x 10(-2)mu(B), below T-C = 140 mK. Above T-C, the muon-spin polarization P(t, B) is dominated by quasihomogeneous spin fluctuations and exhibits a time-field scaling relation P(t, B) = P(t/B-gamma), indicating cooperative critical spin dynamics in the system. At T = 190 mK, slightly above T-C, gamma = 0.81(5), suggesting time-scale invariant power-law behavior for the dynamic electronic spin-spin autocorrelation function.