Transitions in Sr₂Ru_xIr_1-xO₄ compounds studied by the ⁹⁹Ru mössbauer effect

The ⁹⁹Ru Mössbauer effect has been measured in the Sr₂Ru_xIr_1-xO₄ system for x = 1.0, 0.7, 0.5, and 0.4 at 4.2 K. The isomer shift measurements show a change of -0.05(.02) mm/s as the compound changes from a metal (x = 0.7) to an insulator (x = 0.5). This isomer shift change is the electronic signature of the metal-insulator transition. All these spectra are single line. At x = 0.4 the compound undergoes a magnetic phase transition with the measurement of a hyperfine magnetic field of 7.2(1.5) T. The ⁹⁹Ru Mössbauer effect has been measured from 1.8 to 147.5 K for Sr₂RuO₄ and from these measurements the Debye temperature was estimated to be 427(50) K.