Quasiquartet CEF ground state with possible quadrupolar ordering in the tetragonal compound YbRu$_{2}$Ge$_{2}$

TL;DR

This study reveals that YbRu$_{2}$Ge$_{2}$ has a quasiquartet crystal electric field ground state and exhibits complex ordering phenomena, likely involving quadrupolar order, with a notably high ordering temperature among Yb compounds.

Contribution

It is the first to identify a quasiquartet CEF ground state and suggest quadrupolar ordering in YbRu$_{2}$Ge$_{2}$, highlighting its unique magnetic properties among Yb-based materials.

Findings

YbRu$_{2}$Ge$_{2}$ has a stable trivalent Yb state.

Anomalies at T$_{0}$, T$_{1}$, T$_{2}$ indicate complex ordering.

The CEF ground state is a quasiquartet, not a doublet.

Abstract

e have investigated the magnetic properties of YbRu$_{2}$Ge$_{2}$ by means of magnetic susceptibility $\chi$(T), specific heat C(T) and electrical resistivity $\rho$(T) measurements performed on flux grown single crystals. The Curie-Weiss behavior of $\chi$(T) along the easy plane, the large magnetic entropy at low temperatures and the weak Kondo like increase in $\rho$(T) proves a stable trivalent Yb state. Anomalies in C(T), $\rho$(T) and $\chi$(T) at T$_{0}$ = 10.2 K, T$_{1}$ = 6.5 K and T$_{2}$ = 5.7 K evidence complex ordering phenomena, T$_{0}$ being larger than the highest Yb magnetic ordering temperature found up to now. The magnetic entropy just above T$_{0}$ amounts to almost Rln4, indicating that the crystal electric field (CEF) ground state is a quasiquartet instead of the expected doublet. The behavior at T$_{0}$ is rather unusual and suggest that this transition is related to quadrupolar ordering, being a consequence of the CEF quasiquartet ground state. The combination of a quasiquartet CEF ground state, a high ordering temperature, and the relevance of quadrupolar interactions makes YbRu$_{2}$Ge$_{2}$ a rather unique system among Yb based compounds.