Antiferromagnetic order in the honeycomb Kondo lattice <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Ce</mml:mi><mml:msub><mml:mi>Pt</mml:mi><mml:mn>6</mml:mn></mml:msub><mml:msub><mml:mi>Al</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math> induced by Pd substitution
Ryohei Oishi, Kazunori Umeo, Yasuyuki Shimura, Takahiro Onimaru, A. M. Strydom, T. Takabatake
Abstract
The cerium-based compound $\mathrm{Ce}{\mathrm{Pt}}_{6}{\mathrm{Al}}_{3}$, in which Ce atoms form a honeycomb lattice hosting magnetic frustration, has a heavy-fermion ground state. We have observed development of magnetic order in partially Pd-substituted $\mathrm{Ce}{({\mathrm{Pt}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x})}_{6}{\mathrm{Al}}_{3}$ series up to $x$ = 0.3 by the measurements of magnetic susceptibility, electrical resistivity \ensuremath{\rho}, and specific heat $C$. In the whole range of $x$, the unit cell volume remains unchanged within 0.2%, and the effective magnetic moment stays at $2.4\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{B}/\mathrm{Ce}$. For $x$ = 0.05, both $C/T$ and $\ensuremath{\rho}(T)$ jump on cooling at ${T}_{m}=1.8\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. With increasing $x$ to 0.2, ${T}_{m}$ increases to 3.8 K, where $C/T$ shows a pronounced \ensuremath{\lambda}-type anomaly. Application of magnetic fields suppresses ${T}_{m}$, which is indicative of an antiferromagnetic (AFM) ordered state. Thus, a long-range AFM order is induced by the substitution of isovalent Pd for Pt in $\mathrm{Ce}{\mathrm{Pt}}_{6}{\mathrm{Al}}_{3}$ without carrier doping and chemical pressure. We attribute the emergence of AFM order in $\mathrm{Ce}{({\mathrm{Pt}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x})}_{6}{\mathrm{Al}}_{3}$ to the randomness in the spin-orbit interaction in the Pt-Pd sublattice, which weakens both the coherent Kondo effect and magnetic frustration in the honeycomb Kondo lattice.