Anisotropic magnetism and antiferromagnetic ordering in the Kondo-lattice compound YbCuAs2

Abstract

Single crystals of $R\mathrm{Cu}{\mathrm{As}}_{2}$ ($R=\mathrm{Yb}$ and Y) have been synthesized from high temperature ternary melts and their physical properties investigated by magnetization, electrical resistivity, specific heat, and $\ensuremath{\mu}\mathrm{SR}$ measurements. Magnetization measurements of $\mathrm{Yb}\mathrm{Cu}{\mathrm{As}}_{2}$ suggest that $4f$ electrons are almost localized and the observed magnetic properties are influenced by the Kondo and Ruderman-Kittel-Kasuya-Yosida interactions as well as crystalline electric field (CEF) effect. Electrical resistivity measurements show typical Kondo-lattice behavior with a broad local maximum around $\ensuremath{\sim}125\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and a secondary hump around $\ensuremath{\sim}20\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, suggesting a strong hybridization between $4f$ and conduction electrons. A small residual resistivity $(\ensuremath{\sim}0.68\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm})$ and the large residual resistivity ratio ($\mathrm{RRR}\ensuremath{\sim}150$) indicate a high quality single crystal. An analysis of the specific heat data indicates that the ground state doublet is well separated from excited CEF levels. Although an earlier neutron scattering experiment on powdered $\mathrm{Yb}\mathrm{Cu}{\mathrm{As}}_{2}$ samples observed no magnetic Bragg peaks associated with magnetic ordering, thermodynamic and transport property measurements in this study clearly indicate antiferromagnetic ordering below ${T}_{N}=3.7\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ which is also supported by a muon spin relaxation investigation of $\mathrm{Yb}\mathrm{Cu}{\mathrm{As}}_{2}$ single crystals. The Kondo temperature (${T}_{K}$) estimated from the magnetic entropy and magnetic susceptibility is in the range $5--7.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which is of similar magnitude as ${T}_{N}$. Interestingly, magnetization, specific heat, and electrical resistivity measurements as a function of magnetic field show a hysteresis loop both below and above ${T}_{N}$.