Tuning the structural and antiferromagnetic phase transitions in UCr${}_2$Si${}_2$: hydrostatic pressure and chemical substitution

Abstract

Structural phase transitions in $f$-electron materials have attracted sustained attention both for practical and basic science reasons, including that they offer an environment to directly investigate relationships between structure and the $f$-state. Here we present results for UCr${}_2$Si${}_2$, where structural (tetragonal $\to$ monoclinic) and antiferromagnetic phase transitions are seen at $T_{\mathrm{S}}$ $=$ 205 K and $T_{\mathrm{N}}$ $=$ 25 K, respectively. We also provide evidence for an additional second order phase transition at $T_{\mathrm{X}}$ = 280 K. We show that $T_{\mathrm{X}}$, $T_{\mathrm{S}}$, and $T_{\mathrm{N}}$ respond in distinct ways to the application of hydrostatic pressure and Cr $\to$ Ru chemical substitution. In particular, hydrostatic compression increases the structural ordering temperature, eventually causes it to merge with $T_{\mathrm{X}}$ and destroys the antiferromagnetism. In contrast, chemical substitution in the series UCr${}_{2-x}$Ru${}_x$Si${}_2$ suppresses both $T_{\mathrm{S}}$ and $T_{\mathrm{N}}$, causing them to approach zero temperature near $x$ $\approx$ 0.16 and 0.08, respectively. The distinct $T-P$ and $T-x$ phase diagrams are related to the evolution of the rigid Cr-Si and Si-Si substructures, where applied pressure semi-uniformly compresses the unit cell and Cr $\to$ Ru substitution results in uniaxial lattice compression along the tetragonal $c$-axis and an expansion in the $ab$-plane. These results provide insights into an interesting class of strongly correlated quantum materials where degrees of freedom associated with $f$-electron magnetism, strong electronic correlations, and structural instabilities are readily controlled.

Main text 9 pages, 7 figures. Supplementary materials included at the end