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.