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 N\'eel temperature of 9.5^∘{}K. The maximum value of w occurs above TN at about 9.8^∘{}K, while the slope dw/dT has a positive peak at TN. This is the first experimental evidence for a divergent dw/dT in a metallic magnet. The Lorentz number has a monotonic temperature dependence with dL/dT maximum at TN.