TIME-DEPENDENT EFFECTS IN THE FERROMAGNETIC SUSCEPTIBILITY OF TB-II

Measurements of the low field (H(p) = 1-2000 Am-1; f(p) = 100-1000 Hz) ac magnetic susceptibility, transient enhancement of the susceptibili ty and temperature modulation of the susceptibility on single crystal and polycrystalline terbium are reported. For the ferromagnetic region (T(C) almost-equal-to 221 K), temperature hysteresis and time depende nce in susceptibility as well as the detailed response of the suscepti bility to temperature changes are shown to be due to the temperature d ependent domain structures and the motion of the mobile domain wall pi nning centres. The temperature dependence of the diffusion times for t hese centres is consistent with an activation energy almost-equal-to 0 .5 eV, similar to those for impurities and dislocations.