Competing interactions and anisotropic magnetoresistance in layeredCeTe2

On a single crystal of ${\mathrm{CeTe}}_{2}$ with a layered tetragonal structure, we have studied the effect of magnetic field on magnetic susceptibility $M/B,$ specific heat C, and electrical resistivity \ensuremath{\rho}. It is confirmed that this compound orders antiferromagnetically at ${T}_{N}=4.4\mathrm{K},$ while $\ensuremath{\rho}(T)$ shows no anomaly at ${T}_{N}$ but a sharp peak at ${T}_{\ensuremath{\rho}}=6.1\mathrm{K}.$ Below ${T}_{\ensuremath{\rho}},$ $M/B$ rises suddenly for $B\ensuremath{\parallel}c,$ the easy magnetization axis, suggesting the onset of a short-range ferromagnetic order. At 2 K, $M(B\ensuremath{\parallel}c)$ shows a metamagnetic transition at a small field of 0.06 T from the antiferromagnetic ground state to a field-induced ferromagnetic state. The peak in $C(T)$ shifts from 4.3 K in zero field to 4.0 K in ${B}_{\ensuremath{\parallel}C}=0.1\mathrm{T},$ and furthermore a shoulder appears at 4.3 K. With increasing magnetic field, the shoulder changes to a broadened maximum, which shifts towards higher temperatures. These observations indicate that the ferromagnetic interaction competes with the antiferromagnetic one even in zero field. A large negative magnetoresistance, $\mathrm{MR}=[\ensuremath{\rho}(B)\ensuremath{-}\ensuremath{\rho}(0)]/\ensuremath{\rho}(0),$ was observed in the vicinity of ${T}_{\ensuremath{\rho}}.$ For $I\ensuremath{\parallel}c,$ the MR amounts to -25% at 3 T for $B\ensuremath{\parallel}c,$ which is twice that for $B\ensuremath{\perp}c.$ The large MR for $I\ensuremath{\parallel}B\ensuremath{\parallel}c$ is a result of the increase of the c-axis conduction in the field-induced ferromagnetic alignment of Ce spins. However, the MR for $I\ensuremath{\perp}c$ is essentially the same for $B\ensuremath{\parallel}c$ and $B\ensuremath{\perp}c,$ suggesting the confinement of carriers within the Te sheet sandwiched by the ferromagnetically coupled CeTe layers.