Observation of an Anomaly in the Thermal Resistivity and the Lorentz Number of the Metallic Antiferromagnet CeAl

A 20% peak in the thermal resistivity $w$ is observed in the temperature interval 7 to 12°K for CeAl, an antiferromagnet with a Néel temperature of 9.5°K. The maximum value of $w$ occurs above $T_{\mathrm{N}}$ at about 9.8°K, while the slope $\frac{\mathrm{dw}}{\mathrm{dT}}$ has a positive peak at $T_{\mathrm{N}}$. This is the first experimental evidence for a divergent $\frac{\mathrm{dw}}{\mathrm{dT}}$ in a metallic magnet. The Lorentz number has a monotonic temperature dependence with $\frac{\mathrm{dL}}{\mathrm{dT}}$ maximum at $T_{\mathrm{N}}$.