Phase diagram and thermal expansion measurements on the system of URu_{2-x}Fe_xSi_2

TL;DR

This study investigates the phase transitions and thermal expansion behavior of URu_{2-x}Fe_xSi_2 single crystals, revealing distinct features near the HO-LMAFM boundary and significant changes in pressure derivatives across phases.

Contribution

It provides new insights into the thermal expansion signatures of phase transitions in URu_{2-x}Fe_xSi_2 and identifies features unique to thermal expansion measurements.

Findings

Distinct thermal expansion features at phase boundaries

Two separate features near the HO-LMAFM boundary

Dramatic change in pressure derivatives across phases

Abstract

Thermal expansion, electrical resistivity, magnetization, and specific heat measurements were performed on URu$_{2-x}$Fe$_{x}$Si$_{2}$ single crystals for various values of the Fe concentration $x$ in both the hidden order (HO) and large moment antiferromagnetic (LMAFM) regions of the phase diagram. Our results show that the paramagnetic (PM) to HO and LMAFM phase transitions are manifested differently in the thermal expansion coefficient. For Fe concentrations near the boundary between the HO and LMAFM phases at $x_c$ ~ 0.1, we observe two features in the thermal expansion upon cooling, one that appears to be associated with the transition from the PM to the HO phase and another one at lower temperature that may be due to the transition from the HO to the LMAFM phase. These two features have not been observed in other measurements such as specific heat or neutron scattering. In addition, the uniaxial pressure derivative of the transition temperature, based on a calculation using thermal expansion and specific heat data, changes dramatically when crossing from the HO to the LMAFM phase.