CeCoAl4: An incommensurate antiferromagnet.

Abstract

The orthorhombic compound ${\mathrm{CeCoAl}}_{4}$ orders antiferromagnetically at a relatively high N\'eel temperature ${\mathit{T}}_{\mathit{N}}$ of 13 K. The resistivity of ${\mathrm{CeCoAl}}_{4}$ shows a sharp increase near the magnetic transition before decreasing with temperature below 12 K. We believe that such behavior is due to the energy gaps induced by the incommensurate antiferromagnetic order. We have also studied the solid solutions ${\mathrm{La}}_{\mathit{x}}$${\mathrm{Ce}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{CoAl}}_{4}$ for x=0.1 and 0.2 and ${\mathrm{CeCo}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$${\mathit{T}}_{\mathit{y}}$${\mathrm{Al}}_{4}$ for T=Ni, Cu, and Pd. The crystal structure changes to ${\mathrm{YNiAl}}_{4}$-type even at low values of y (y\ensuremath{\approxeq}0.1 and T=Ni and Pd). We find that ${\mathit{T}}_{\mathit{N}}$ decreases when La or Cu is substituted for Ce and Co, respectively. The sharp increase in the resistivity near ${\mathit{T}}_{\mathit{N}}$ in ${\mathrm{CeCoAl}}_{4}$ is almost smeared out in these pseudoternaries.