TEMPERATURE-DEPENDENCE OF THE SAMARIUM MAGNETIC FORM-FACTOR IN SMCO5

Results of polarized neutron experiments on SmCo5 at 4.2 K and 300 K are reported. To overcome the problem of the huge Sm absorption the measurements were made at short wavelengths, but on a single crystal containing natural samarium. The Co moments are close to those found in YCo5. The Sm form factor is very different at 4.2 K and 300 K, giving direct evidence for exchange and crystal field mixing of excited multiplets into the ground multiplet. The Sm moment is smaller at 300 K than at 4.2 K and its orbital character is less pronounced. The cross-over is calculated to occur at 350 K above which temperature the spin contribution exceeds the orbital one. The compound is ferromagnetic below the cross-over and ferrimagnetic above. The exchange and crystal field parameters deduced from our results are in agreement with previous determinations [1].