Anisotropy of the T vs. H phase diagram and the HO/LMAFM phase boundary in URu2−xFexSi2

Abstract

The correlated f-electron compound URu2Si2 exhibits superconductivity (SC) with a critical temperature Tc = 1.5 K that coexists with the “hidden order” (HO) phase that forms below a characteristic temperature T0 = 17.5 K. The SC of URu2Si2 appears to be spin singlet chiral SC with d-wave order parameter symmetry, and the pairing of SCing electrons may involve spin excitations of the HO phase. Electrical resistance R measurements were performed on single crystal specimens of URu2−xFexSi2 with increasing x throughout the transition from the HO phase to the large moment antiferromagnetic LMAFM phase in high magnetic fields H oriented at various angles θ with respect to the tetragonal c-axis. Measurements of R(θ) at H = 20, 33, 40, and 45 T were conducted in the temperature range 0.33 ≤ T ≤ 20 K and showed θ-dependent behavior in the various phase transitions of URu2−xFexSi2 (HO, LMAFM, spin density wave, Fermi surface reconstruction, etc.). These phase transitions, as functions of T, H, and θ are plotted in a phase diagram of T vs. H//c = Hcosθ for multiple values of x and show that H//c, not θ is a tuning parameter of the URu2−xFexSi2 system throughout all Fe concentrations, as previously found by Scheereret al. for the URu2Si2 parent compound.