Unusual weak magnetic exchange in two different structure types: YbPt$_2$Sn and YbPt$_2$In

TL;DR

This study investigates two Yb-based compounds with different structures, revealing very weak magnetic exchange interactions, short-range magnetic order at millikelvin temperatures, and potential for magnetic cooling applications, along with a charge density wave transition in one compound.

Contribution

It reports the discovery and characterization of two new YbPt$_2$X compounds with distinct structures but similar weak magnetic interactions and low-temperature magnetic ordering.

Findings

Weak exchange interactions below 1K

Short-range magnetic order at ~250mK and ~180mK

Charge density wave transition at ~290K in YbPt$_2$In

Abstract

We present the structural, magnetic, thermodynamic, and transport properties of the two new compounds YbPt$_2$Sn and YbPt$_2$In. X-ray powder diffraction shows that they crystallize in different structure types, the hexagonal ZrPt$_2$Al and the cubic Heusler type, respectively. Despite quite different lattice types, both compounds present very similar magnetic properties: a stable trivalent Yb$^{3+}$, no evidence for a sizeable Kondo interaction, and very weak exchange interactions with a strength below 1K as deduced from specific heat $C(T)$. Broad anomalies in $C(T)$ suggest short range magnetic ordering at about 250mK and 180mK for YbPt$_2$Sn and YbPt$_2$In, respectively. The weak exchange and the low ordering temperature result in a large magnetocaloric effect as deduced from the magnetic field dependence of $C(T)$, making these compounds interesting candidates for magnetic cooling. In addition we found in YbPt$_2$In evidences for a charge density wave transition at about 290K. The occurrence of such transitions within several RET$_2$X compound series (RE = rare earth, T = noble metal, X = In, Sn) is analyzed.