Chemical pressure tuning of URu₂Si₂ via isoelectronic substitution of Ru with Fe

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We have used specific heat and neutron diffraction measurements on single crystals of URu₂₋ₓFeₓSi₂ for Fe concentrations x ≤ 0.7 to establish that chemical substitution of Ru with Fe acts as "chemical pressure" Pch as previously proposed by Kanchanavatee et al. [Phys. Rev. B 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 Pₓ≈ 0.5-0.7 GPa in URu₂Si₂. Using the unit cell volume determined from our measurements and an isothermal compressibility κₜ = 5.2 × 10⁻³ GPa⁻¹ for URu₂Si₂, we determine the chemical pressure Pch in URu₂₋ₓFeₓSi₂ as a function of x. The resulting temperature T-chemical pressure Pch phase diagram for URu₂₋ₓFeₓSi₂ is in agreement with the established temperature T-external pressure P phase diagram of URu₂Si₂.