Interplay between Charge and Magnetic Ordering in YbPd

TL;DR

This study investigates the pressure-temperature phase diagram of YbPd, revealing how structural and magnetic transitions interact and evolve under pressure, highlighting the complex interplay between charge and magnetic ordering in this intermediate-valence compound.

Contribution

It provides detailed experimental insights into the pressure-dependent structural and magnetic phase transitions in YbPd, including the suppression of magnetic order and structural changes at critical pressures.

Findings

Magnetic ordering temperature decreases with pressure and vanishes at 1.9 GPa.

Structural phase transition at T2 is suppressed at the same critical pressure.

Enhanced effective mass observed near the critical pressure.

Abstract

The pressure-temperature phase diagram of an intermediate-valence compound YbPd was revealed via simultaneous ac-calorimetry and electrical resistivity measurements. Two successive structural phase transition temperatures, $T_1$ = 125 K and $T_2$ = 110 K, are found to decrease with increasing pressure. The magnetic ordering transition at $T_{\rm N} ~sim$ 1.9 K decreases monotonically up to 1.7 GPa and disappears discontinuously at $P_{\rm c} sim$ 1.9 GPa, where the structural phase transition at $T_2$ is also suppressed. At $P_{\rm c}$, enhancement of the effective mass and residual resistivity are observed. Another probable magnetic phase transition, however, is found to take place at $T_{\rm ML} sim$0.3 K and smoothly varies even when crossing $P_{\rm c}$. Structural phase transitions at ambient pressure were also studied by a single crystal X-ray diffraction measurement. Below $T_2$, a tetragonal lattice distortion with doubling of the unit cell along the c-axis is observed, and thus there are two inequivalent Yb-sites below $P_{\rm c}$. These results indicate that one Yb-site, having larger valence configuration and thus smaller Kondo temperature, orders at $T_{\rm N}$. The other phase transition at $T_{\rm ML}$ seems to couple to the crystal structure for $T_2 < T < T_1$. YbPd is a unique system exhibiting magnetic orderings in metallic charge-ordered Yb systems.