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

Abstract

We present investigations on the magnetic susceptibility x(T), the specific heat coefficient g(T) ¼ C(T)/T, and the spin-lattice relaxation (SLR) rate on the two isostructural iron aluminides YFe 2 Al 10 and YbFe 2 Al 10 . Below 10 K, both systems display a monotonous field-dependent increase with decreasing temperature in x(T), g(T) and the SLR coefficient 27 R(T) ¼ 27 (1/T 1 T). 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-T upturn in the properties. The comparison between zero-field and high field measurements allow for the determination of enhancement factors in x(T), the g(T), and the spin-lattice relaxation coefficient (SLRC) 27 R(T). Surprisingly, the relative enhancement in g(T) and the T-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 for T ! 0. The divergences are very similar because the Yb ions in YbFe 2 Al 10 are 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 dominant q ¼ 0 low-energy FM spin fluctuations from weak itinerant Fe as the origin for the observed logarithmic divergences.

Contiguous3dand4fMagnetism: Strongly Correlated3dElectrons inKhuntia1, Peratheepan2, Strydom3 et al. 2014Phys. Rev. Lett.Self Cite17071View full textAdd to dashboardCite

“…The magnetism of Yb in this compound was demonstrated [38] to be subject to an unstable valence and to recover its full trivalent state at T > 400 K, which is in agreement with earlier reports [39].…”

“…The ratio of the enhanced γ 0 value at zero field to the fully quenched value γ H in 9 T at 0.35 K is about 2.5. Surprisingly, this enhancement factor is qualitatively similar to that of the non-4f compound YFe 2 Al 10 [38]. Despite the fact that the relative enhancements Δγ=γ H ¼ ðγ 0 − γ H Þ=γ H are similar, it should be mentioned that the T dependencies of C p =T are dissimilar: [lnðT 0 =TÞ for YbFe 2 Al 10 and power law behavior in the case of YFe 2 Al 10 ].…”

“…3). Surprisingly, we found a rather well-resolved central transition with a small field dependent anisotropy, which implies that the different Al sites are rather equal in their magnetic environment [21,38].…”

Anomalous rattling and single crystalline properties of the caged compound URu2Al10

“…In this orthorhombic structure, the T-atoms are stacked in twodimensional (2D) planes perpendicular to the b-axis. This layout means that SFs reside here mainly in the ac plane, and the Sommerfeld coefficient γ(0 K) of YFe 2 Al 10 is increased to 25 mJ mol -1 K -2 [29], while this value falls to 8.3 mJ mol -1 K -2 for YRu 2 Al 10 [30]. This observation and that for LaFe 2 Al 10 [26] emphasize the special role of the Fe atoms in such cage-like ternaries.…”

Single-crystal growth and physical property characterization of the intermediate-valence compound YbFe2Al10

“…Nevertheless, the Yb-based RT 2 Al 10 seems to be much less investigated, partially due to the difficulty of growing single crystalline samples with good quality. Among them, YbFe 2 Al 10 was found to be an intermediate valence candidate in which Yb shows +3 state at high temperatures above 400 K but fluctuates at lower temperatures [24,25]. However, the Kondo lattice type characters only presented themselves at very low temperatures below 10 K, which is in conflict with the expected strong hybridization strength for intermediate valence compounds.…”