Unexpected Resistivity Upturn In A Highly-Localized Gd-System

Synopsis

The family of intermetallic compounds, RCuAs₂ (R = Nd, Sm, Gd, Tb, and Dy), exhibit a pronounced resistivity upturn above their antiferromagnetic ordering temperatures (T_N). Although this upturn is frequently observed in Kondo materials, the same mechanism cannot be applied to these highly localized 4f-moment systems. To identify the origin of the resistivity upturn, Gd-based compounds are studied since Kondo and crystalline electric field effects are absent in this system.  Single crystals of Gd_xY_1-xCuAs₂ were synthesized and characterized by magnetization, specific heat, and resistivity measurements. GdCuAs₂ shows a non-logarithmic resistivity upturn above T_N = 10.6 K. Although the physical property measurements show a suppression of T_N below x ~ 0.48, the resistivity upturn persists throughout the entire doping range. A proposed contribution to resistivity, the frustrated RKKY interaction shows good agreement down to the lowest Gd-concentrations. Magnetic susceptibility measurements for x ~ 0.48 indicate a broad local maximum, suggesting a spin-glass-like state caused by disorder or magnetic frustration.