Anisotropy of the T vs. H phase diagram and the HO-LMAFM boundary in URu_2-xFe_xSi₂

We explored the role of angle, θ, as a tuning parameter in URu_2-xFe_xSi₂, where θ is the angle between the magnetic field, H, and the c-axis. We first investigated the parent compound URu₂Si₂ by measuring electrical resistance, R, vs. H, at several selected θ, for temperatures T = 1.5, 10, and 13 K. We observed that R(H) scaled with the projection of the magnetic field onto the c-axis, and therefore the θ- and H-dependent behavior of R, including the so-called "hidden order" (HO) transition and the Fermi surface reconstruction in URu₂Si₂, at fixed T, demonstrate that R(θ, H) is actually dependent on H//c = H cosθ, consistent with a similar study reported previously. We continued this investigation on URu_2-xFe_xSi₂ to observe whether θ becomes a tuning parameter as Fe substitution increases and the system is driven toward large-moment antiferromagnetic order (LMAFM). Measurements on R(θ) at μ₀H = 20, 33, 40, and 45 T were conducted at 0.33 ≤ T ≤ 20 K and showed θ-dependent behavior in the various phase transitions of URu_2-xFe_xSi₂ (HO, LMAFM, SDW, Fermi surface, etc.). These phase transitions, as functions of T, H, and θ were plotted in a phase diagram of T vs. H//c for multiple x and reaffirmed that H//c, not θ, is a tuning parameter of URu_2-xFe_xSi₂ throughout all Fe concentrations.