Hyperfine resonance properties ofEr3+in Au

The direct hyperfine resonance spectra of the ${\Gamma }_7$ ground state of isotopically enriched ${}_{}{}^{167}{}_{}{}^{}\mathrm{Er}_{}^{3+}{}_{}{}^{}$ in a dilute Au matrix have been measured in the millikelvin temperature region at frequencies of 230-300 MHz. The spectra were fitted to an isotropic spin Hamiltonian with the magnetic hyperfine constant $A$ and the pseudonuclear $g$ factor ${g_n}^{\prime }$ as fitting parameters. Knowledge of ${g_n}^{\prime }$ makes it possible to estimate the energy separation $\Delta$ of the first-excited ${\Gamma }_8^{\mathrm{}\left(1\right)\mathrm{}}$ quartet from the ground state. This separation was found to be 11 ± 2 K which is in fair agreement with reported measurements at $X$ band, where $\Delta =16\mathrm{}\pm 6$ K. The hyperfine constant $A$ deduced from the rf spectrum is negative and $\mathrm{}\left|A\right|\mathrm{}$ is approximately 2% smaller than the $A$ value derived from the $X$-band spectrum. The linewidth is of the form $a\left(H\right)+bT$, where $b=13\mathrm{}$ G/K and the residual linewidth $a \mathrm{}\left(H\right)\mathrm{}$ is a function of magnetic field.