Moment un-freezing in iridium substituted Sr₂RuO₄

We report data suggestive of a J-freezing metallic quantum critical point in paramagnetic Sr₂Ir_xRu_1-xO₄. Electron doping from the d⁴ compound Sr₂RuO₄ though a transition near x=18% yields an abrupt increase in the static effective moment magnitude as well as the antiferromagnetic fluctuations. We present thermodynamic measurements of high-quality floating-zone-synthesized single crystal samples. Our findings may indicate a novel critical point neighboring the nonmagnetic ground state of the correlated metal Sr₂RuO₄.