Proton spin-lattice relaxation data ${\mathit{R}}_1$ (1/${\mathit{T}}_1$) are reported for the solid solution ${\mathrm{Nb}}_{0.5}$${\mathrm{V}}_{0.5}$${\mathrm{H}}_{0.36}$. In the region of the previously reported anomaly (T>700 K), a strong frequency dependence is observed by extending the measurements to a high frequency, 341 MHz. The correlation time ${\mathrm{\tau }}_{\mathit{c}}$ is determined and is found to decrease with increasing temperature. The mean-square magnetic-field fluctuation ${\mathit{M}}_2$ responsible for the relaxation is also determined. Surprisingly, ${\mathit{M}}_2$ increases rapidly with increasing temperature, suggesting an excited state with a large spin interaction, such as molecular hydrogen.

• Received 4 October 1991

DOI:https://doi.org/10.1103/PhysRevB.46.184