Chemical pressure tuning of URu${}_2$Si${}_2$ via isoelectronic substitution of Ru with Fe

We have used specific heat and neutron diffraction measurements on single crystals of URu${}_{2-x}$Fe${}_x$Si${}_2$ for Fe concentrations $x$ $\le$ 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$^{-1}$forURu$2$Si$2$,wedeterminethechemicalpressure$P{ch}$inURu${2-x}$Fe$_x$Si$_2$asafunctionof$x$. 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${}_2$.