Mössbauer study of the Ising antiferromagnet DyPO4: Hyperfine parameters,g-factor anisotropy, and spin-lattice relaxation

Mössbauer spectroscopy of the 26-keV $\gamma$-ray transition in ${}_{}{}^{161}{}_{}{}^{}\mathrm{Dy}$ was employed to study nuclear hyperfine interactions in Ising-like DyP${\mathrm{O}}_4$. Single-crystal and polycrystalline samples were studied over the temperature range $1.8\le T\lesssim 300$ K, which included the Néel temperature $T_N=3.39\mathrm{}$ K. For $0\le T\lesssim 10$ K the spectra could be analyzed in terms of a "static" $S=\frac{1}{2}$ spin Hamiltonian $\mathcal{H}=A_z{I}_z{S}_z+\left(\frac{A_{\perp }}{2}\right)(I^{+}{S}^{-}+I^{-}{S}^{+})+P[3\mathrm{}{I}_z^2-I(I+1\mathrm{}\left)\right]$. The measured components of the magnetic hyperfine tensor parallel and perpendicular to the tetragonal $c$ axis are, respectively, $\frac{A_z}{2}=-831\mathrm{}\pm 4$ MHz and $A_{\perp }=-14\mathrm{}\pm 5$ MHz. This is the first reported measurement of an $A_{\perp }$ term in Mössbauer studies of dysprosium compounds. Using the known ionic $g$-factor component, $g_z=19.32\mathrm{}\pm 0.01$, we calculate $k=\frac{A_z}{2h{g}_z}=43.0\mathrm{}\pm 0.2$ and hence $g_{\perp }=0.3\mathrm{}\pm 0.1$. The ratio of quadrupole parameters for the excited and ground nuclear states of ${}_{}{}^{161}{}_{}{}^{}\mathrm{Dy}$ is $\frac{P_e}{P_g}=0.986\mathrm{}\pm 0.003$ with $\frac{P_g}{h}=60.3\mathrm{}\pm 0.6$ MHz. For $T\gtrsim 10$ K the spectra are relaxation broadened and can be described well using the time-dependent Hamiltonian