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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) \times 10-2μB, below TC = 140 mK. Above TC, 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/Bγ), indicating cooperative critical spin dynamics in the system. At T = 190 mK, slightly above TC, γ = 0.81(5), suggesting time-scale invariant power-law behavior for the dynamic electronic spin-spin autocorrelation function.