Crystal-Field Effects in the Magnetic Form Factor of TmSb

The magnetic form factor of TmSb in an applied magnetic field of 12.5 kOe at 5 °K has been measured with polarized neutrons. The experimental points with $H\parallel 〈100〉$ fall on a smooth curve, whereas considerable anisotropy is observed with $H\parallel 〈110〉$. These effects arise from the interaction between the rare-earth ion and the crystal field. The agreement between the theoretical form factor, calculated by the tensor-operator method, and the experiment is excellent.