Long-range magnetic order in the anisotropic triangular lattice system <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>CeCd</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>As</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>
S. R. Dunsiger, J. Lee, J. E. Sonier, Eundeok Mun
Abstract
We report the physical properties of $R{\mathrm{Cd}}_{3}{\mathrm{As}}_{3}$ ($R$ = La and Ce) compounds, crystallized into a hexagonal ${\mathrm{ScAl}}_{3}{\mathrm{C}}_{3}$-type structure ($P{6}_{3}$/mmc) such that the $R$ sublattice forms a spin-orbit coupled triangular lattice. Magnetic susceptibility measurements indicate the $4f$ electrons of ${\mathrm{Ce}}^{3+}$ ions are well localized and reveal a large magnetic anisotropy. The electrical resistivity and specific heat measurements for $R{\mathrm{Cd}}_{3}{\mathrm{As}}_{3}$ exhibit an anomaly at high temperatures (${T}_{0}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}$ 63 K for $R$ = La and ${T}_{0}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}$ 136 K for $R$ = Ce), most likely due to a structural transition. Specific heat measurements for ${\mathrm{CeCd}}_{3}{\mathrm{As}}_{3}$ clearly indicate a long-range magnetic order below ${T}_{N}$ = 0.42 K. Although the magnetic contribution to the specific heat ${C}_{m}/T$ increases significantly below $\ensuremath{\sim}10$ K, the electrical resistivity for ${\mathrm{CeCd}}_{3}{\mathrm{As}}_{3}$ follows the typical, metallic behavior inconsistent with Kondo lattice systems. In ${\mathrm{CeCd}}_{3}{\mathrm{As}}_{3}$ only $\ensuremath{\sim}40 %$ of the $Rln(2)$ magnetic entropy is recovered by ${T}_{N}$ and the $R\mathrm{ln}$(2) entropy is fully achieved at about the Curie-Weiss temperature $|{\ensuremath{\theta}}_{p}|$. Unusually, based on our current investigations, the magnetic specific heat below $|{\ensuremath{\theta}}_{p}|$ is not attributed to a Kondo contribution, but rather associated with the magnetic ordering and frustration on the triangular lattice. Specific heat measurements in an applied magnetic field show a negligible variation of ${T}_{N}$ for $H\ensuremath{\parallel}c$, whereas a suppression of ${T}_{N}$ is observed above 40 kOe for $H\ensuremath{\parallel}ab$. Such behavior is consistent with the application of a magnetic field within the $ab$-plane breaking the triangular symmetry and partially relieving the magnetic frustration in this system.