Localized moments and the stability of antiferromagnetic order in Yb3Pt4

Abstract

We present here the results of electrical resistivity $\ensuremath{\rho}$, magnetization $M$, ac susceptibility ${\ensuremath{\chi}}_{ac}^{\ensuremath{'}}$, and specific heat ${C}_{\mathrm{M}}$ measurements that have been carried out on single crystals of ${\mathrm{Yb}}_{3}{\mathrm{Pt}}_{4}$ over a wide range of fields and temperatures. The 2.4-K N\'eel temperature that is found in zero field collapses under field to a first-order transition ${T}_{\mathrm{N}}=0$ at ${B}_{\mathrm{CEP}}=1.85$ T. In the absence of antiferromagnetic order, the specific heat ${C}_{\mathrm{M}}(T,B)$, the magnetization $M(T,B)$, and even the resistivity $\ensuremath{\rho}(T,B)$ all display $B/T$ scaling, indicating that they are dominated by strong paramagnetic fluctuations, where the only characteristic energy scale results from the Zeeman splitting of an energetically isolated, Yb doublet ground state. This paramagnetic scattering disappears with the onset of antiferromagnetic order, revealing Fermi liquid behavior $\ensuremath{\Delta}\ensuremath{\rho}=A{T}^{2}$ that persists up to the antiferromagnetic phase line ${T}_{\mathrm{N}}(B)$, but not beyond. The first-order character of ${T}_{\mathrm{N}}=0$ and the ubiquity of the paramagnetic fluctuations imply that non-Fermi-liquid behaviors are absent in ${\mathrm{Yb}}_{3}{\mathrm{Pt}}_{4}$. In contrast to heavy fermions such as ${\mathrm{YbRh}}_{2}{\mathrm{Si}}_{2}$, ${\mathrm{Yb}}_{3}{\mathrm{Pt}}_{4}$ represents an extremely simple regime of $f$-electron behavior where the Yb moments and conduction electrons are almost decoupled, and where Kondo physics plays little role.