Magnetic form factor of thulium and terbium metals

Abstract

The magnetic form factors of thulium and terbium have been measured with polarized neutrons. For the two metals the samples that were used in the experiment were single crystals. Both thulium and teroium crystallize in the hexagonal close-packed structure. The form factor of thulium was measured at 4.2 °K and in a magnetic field of 10 kOe applied parallel to the c-axis. The magnetic structure of thulium at 4.2 °K and in low fields (less than 28 kOe) applied parallel to the c-axis is an antiphase domain structure with a net ferromagnetic moment parallel to the c-axis. The magnitude of the moment is 1 iUg fjer atom. In this experiment the magnetic form factor of this ferro­ magnetic moment has been determined. The form factor of terbium was measured at 298 °K and in a magnetic field of 22 kOe applied parallel to both the aand the baxis. Terbium is paramagnetic at 298 and the magnitude of the induced moment in a field of 22 kOe is 0.8 Mg per atom for the two directions of the field. The magnetic form factor of the induced moment has been measured in this experiment. Within the experimental uncertainty the form factors for the directions of the magnetic field were identical. Theoretical form factors has been calculated for both thulium and terbium using the 4f wave functions of Freeman and Watson. A comparison between the theoretical and experimental form factors indicates that the free ion wave functions of Freeman and Watson are too contracted for both metals.