Quenching of spin fluctuations in the 3d and 4f aluminides YFe2Al10and YbFe2Al10: a comparative27Al NMR and specific heat study

Abstract

AbstractWe present investigations on the magnetic susceptibilityχ(T), the specific heat coefficientγ(T) = C(T)/T, and the spin‐lattice relaxation (SLR) rate on the two isostructural iron aluminides YFe2Al10and YbFe2Al10. Below 10 K, both systems display a monotonous field‐dependent increase with decreasing temperature inχ(T),γ(T) and the SLR coefficient27R(T) = 27(1/T1T). These divergences are associated with spin fluctuations near a quantum critical point (QCP). Most probably, the QCP is of ferromagnetic (FM) nature, but so far no magnetic order is observed in either system down to 0.35 K. The application of moderate fields of a few Tesla suppresses the low‐Tupturn in the properties. The comparison between zero‐field and high field measurements allow for the determination of enhancement factors inχ(T), theγ(T), and the spin‐lattice relaxation coefficient (SLRC)27R(T). Surprisingly, the relative enhancement inγ(T) and theT‐dependence [∝ ln(1/T)] are very similar for both systems. In the SLRC, the enhancement is larger for the Yb‐system but both show ln(1/T) behavior forT → 0. The divergences are very similar because the Yb ions in YbFe2Al10are in an intermediate valence state at low temperatures and contribute only very little towards the observed spin fluctuations. This indicates strongly the same underlying physics and the same energy scales for both systems. We propose the presence of dominantq = 0 low‐energy FM spin fluctuations from weak itinerant Fe as the origin for the observed logarithmic divergences.