Unexpected resistivity minimum in a highly-localized Gd-system

The family of intermetallic compounds, RCuAs₂ (R = Nd, Sm, Gd, Tb, and Dy), all exhibit a pronounced resistivity minimum above their antiferromagnetic ordering temperature (T_N). Although the resistivity minimum has been frequently observed in Kondo materials, the same microscopic mechanism cannot be applied to these highly localized 4f-electron systems. To isolate and identify the cause of this behavior we study Gd-based compounds, without the Kondo and crystalline electric field (CEF) effects. Single crystals of Gd_xY_1-xCuAs₂ are synthesized and characterized by magnetization, resistivity, and specific heat measurements. GdCuAs₂ clearly shows a non-logarithmic resistivity upturn above T_N = 10.6 K. Although the thermodynamic and transport property measurements show a suppression of T_N at x ~ 0.3, surprisingly the resistivity minimum persists over the entire doping range. Magnetic susceptibility measurement for x ~ 0.3 indicates a broad local maximum at low temperatures, suggesting a spin glass state caused by disorder or magnetic frustration. In this talk, we show how chemical substitutions influence the resistivity minimum observed in this system and compare it with theoretical models such as the frustrated RKKY mechanism.