A study of low energy magnetic excitations in terbium metaphosphate glass

The existence of a wide distribution of low energy excess magnetic states due to topological disorder in a magnetic glass is confirmed experimentally for the case of terbium metaphosphate glasses with compositions in the vicinity of (Tb2O3)0.25(P2O5) 0.75. A broad peak with a maximum at 7.5 K is found in the magnetic contribution to the specific heat; this has its origin in the excess magnetic states. There is also a residual magnetic contribution from these states to the inelastic neutron scattering, which has been isolated by subtraction of the phonon contribution. Exploiting the paramagnetic behaviour, a novel method of neutron scattering has been investigated, which can be used to isolate the Tb-Tb correlation distances in terbium metaphosphate glass. This method uses the fact that neutrons are sensitive to changes in scattering lengths, and the scattering length of a paramagnetic rare earth ion, in a metaphosphate glass host, can be changed by applying a magnetic field.