The Magnetic Susceptibilities of Alloys of Cerium with Thorium

The paramagnetic susceptibilities of 90, 71, 60, 42, 20, 10 and 5 atomic per cent cerium in thorium alloys have been measured over the temperature range 90°K to 700°K. The temperature dependence of the resistivity of 90, 60, 40, 20 and 5 atomic per cent cerium-thorium alloys has been investigated over the range 90°K to 293°K. The thermal expansion of the 60% alloy has also been measured over this temperature range. All the alloys exhibit a sharp decrease in susceptibility at low temperatures. This has been attributed to the excitation of some of the 4f electrons of the cerium atoms into the conduction band at these temperatures, and the resistivity and expansion results support this hypothesis. Above room temperature the susceptibilities of all the alloys obey a Curie-Weiss law, χ= C /( T - θ), over at least part of the temperature range. The effective magnetic moments per cerium atom calculated from the Curie constants C increased with decreasing cerium content. A model has been proposed in which coupling between the cerium f electron and the conduction electrons causes polarization of the latter in the neighbourhood of the cerium atoms. The apparent increase in p eff is attributed to this induced moment.