Ground-state magnetic resonance of DyPO4in the far infrared

Magnetic resonance has been observed in the Ising system DyP${\mathrm{O}}_4$ utilizing a far-infrared laser magnetic-resonance spectrometer, in applied fields $\overrightarrow{\mathrm{H}}\parallel \overrightarrow{\mathrm{C}}$ sufficient to saturate the spin system. The resonance spectra obtained at 220.23 μm (45.407 ${\mathrm{cm}}^{-1\mathrm{}}$) and 171.67 μm (58.25 ${\mathrm{cm}}^{-1\mathrm{}}$) at 4.2 °K were composed of three superimposed hyperfine patterns. Two of them were six-line patterns, one from ${}_{}{}^{161}{}_{}{}^{}\mathrm{Dy}_{}^{3+}{}_{}{}^{}$ ($I=\frac{5}{2}$) and one from ${}_{}{}^{163}{}_{}{}^{}\mathrm{Dy}_{}^{3+}{}_{}{}^{}$ ($I=\frac{5}{2}$). In addition there was a central line due to even isotopes ($I=0\mathrm{}$). All six lines of ${}_{}{}^{163}{}_{}{}^{}\mathrm{Dy}_{}^{3+}{}_{}{}^{}$ were resolved, yielding a value for the spin-Hamiltonian parameter ${}_{}{}^{163}{}_{}{}^{}\left(\frac{A}{g_{\parallel }}\right)=37.2\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$, while for ${}_{}{}^{161}{}_{}{}^{}\mathrm{Dy}_{}^{3+}{}_{}{}^{}$ we obtained ${}_{}{}^{161}{}_{}{}^{}\left(\frac{A}{g_{\parallel }}\right)=26.6\mathrm{}\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ from the four components which could be resolved. From the two $I=0\mathrm{}$ resonances at 53 338 and 67 579 Oe, we obtain $g_{\parallel }=19.32\mathrm{}$. The effects of a large nonuniform demagnetizing field on the line shape have been observed and analyzed in detail.