J. Spehling

Avoided Ferromagnetic Quantum Critical Point: Unusual Short-Range Ordered State in CeFePO

Cerium 4f electronic spin dynamics in single crystals of the heavy-fermion system CeFePO is studied by means of ac susceptibility, specific heat, and muon-spin relaxation (μSR). Short-range static magnetism occurs below the freezing temperature T(g) ≈ 0.7 K, which prevents the system from accessing a putative ferromagnetic quantum critical point. In the μSR, the sample-averaged muon asymmetry function is dominated by strongly inhomogeneous spin fluctuations below 10 K and exhibits a characteristic time-field scaling relation expected from glassy spin dynamics, strongly evidencing cooperative and critical spin fluctuations. The overall behavior can be ascribed neither to canonical spin glasses nor other disorder-driven mechanisms.

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 10-2{\mu}B, 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/B{\gamma}), indicating cooperative critical spin dynamics in the system. At T = 190 mK, slightly above TC, {\gamma} = 0.81(5), suggesting time-scale invariant power-law behavior for the dynamic electronic spin-spin autocorrelation function.

Interplay of magnetism and superconductivity in EuFe2(As1-xPx)2 single crystals probed by muon spin rotation and 57Fe Mössbauer spectroscopy

We present our results of a local probe study on EuFe2(As1-xPx)2 single crystals with x=0.13, 0.19 and 0.28 by means of muon spin rotation and 57Fe Mossbauer spectroscopy. We focus our discussion on the sample with x=0.19 viz. at the optimal substitution level, where bulk superconductivity (TSC = 28 K) sets in above static europium order (TEu = 20 K) but well below the onset of the iron antiferromagnetic (AFM) transition (~100 K). We find enhanced spin dynamics in the Fe sublattice closely above TSC and propose that these are related to enhanced Eu fluctuations due to the evident coupling of both sublattices observed in our experiments.

Magnetic order and spin dynamics across a ferromagnetic quantum critical point: mu SR investigations of YbNi4(P1-xAsx)2

In the quasi-1D heavy-fermion system YbNi

Ferromagnetism and superconductivity in CeFeAs1-xPxO (0≤x≤40%)

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Ferromagnetism and superconductivity in CeFeAs 1-x Px O ( 0≤x≤40% )

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Ferromagnetism and superconductivity in P-doped CeFeAsO

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Coexistence of superconductivity and magnetism inCa1−xNaxFe2As2: Universal suppression of the magnetic order parameter in 122 iron pnictides

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Structural and electronic phase diagrams of CeFeAsO1-xFx and SmFeAsO1-xFx

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Static and dynamic susceptibility in the putative ferromagnetic quantum critical system YbNi4P2 probed by 31P NMR

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