We have used specific heat and neutron diffraction measurements on single crystals of URu$_{ 2-x}$Fe$_x$Si$_2$ for Fe concentrations $x$ $\leq$ 0.7 to establish that chemical substitution of Ru with Fe acts as "chemical pressure" $P_{ ch}$ as previously proposed by Kanchanavatee et al. [Phys. Rev. B { \bf 84}, 245122 (2011)] based on bulk measurements on polycrystalline samples. Notably, neutron diffraction reveals a sharp increase of the uranium magnetic moment at $x=0.1$, reminiscent of the behavior at the "hidden order" (HO) to large moment antiferromagnetic (LMAFM) phase transition observed at a pressure $P_x\approx$ 0.5-0.7~GPa in URu$_2$Si$_2$. Using the unit cell volume determined from our measurements and an isothermal compressibility $\kappa_{ T} = 5.2 \times 10^{ -3}$ GPa$^{ -1}$ for URu$_2$Si$_2$, we determine the chemical pressure $P_{ ch}$ in URu$_{ 2-x}$Fe$_x$Si$_2$ as a function of $x$. The resulting temperature $T$-chemical pressure $P_{ ch}$ phase diagram for URu$_{ 2-x}$Fe$_x$Si$_2$ is in agreement with the established temperature $T$-external pressure $P$ phase diagram of URu$_2$Si$_2$.
Categories: cond-mat.str-el