Magnetic structures of Dy${\mathrm{Co}}_2$${\mathrm{Si}}_2$ and Dy${\mathrm{Cu}}_2$${\mathrm{Si}}_2$: A neutron-diffraction study

The compounds Dy${\mathrm{Co}}_2$ ${\mathrm{Si}}_2$ and Dy${\mathrm{Cu}}_2$ ${\mathrm{Si}}_2$ were studied by neutron diffraction. The diffraction patterns of these compounds at 300 K agree with the reported crystallographic structures (space group $\frac{I4\mathrm{}}{\mathrm{mmm}}$). The diffraction pattern of Dy${\mathrm{Co}}_2$ ${\mathrm{Si}}_2$ at 4.2 K is consistent with a type-I antiferromagnetic structure on the Dy sublattice. The magnetic moment, $(9.5\mathrm{}\pm 0.5){\mu }_B$, lies along the $c$ axis. The diffraction pattern of Dy${\mathrm{Cu}}_2$ ${\mathrm{Si}}_2$ at 4.2 K revealed the existence of superlattice lines consistent with a cell doubled in the $a$ and $c$ directions. The magnetic structure consists of ferromagnetic (101) planes of Dy coupled antiferromagnetically. The magnetic moment $(8.3\mathrm{}\pm 0.4){\mu }_B$ lies along the $b$ axis. The transition temperatures $T_N$ deduced from the intensity-versus-temperature measurements of the reflections {010} and {½0½} for Dy${\mathrm{Co}}_2$ ${\mathrm{Si}}_2$ and Dy${\mathrm{Cu}}_2$ ${\mathrm{Si}}_2$, respectively, are 21±2 and 11±1 K. It is found that $H_{\mathrm{eff}}\left(\mathrm{kOe}\right)\sim 600\mu \left({\mu }_B\right)$, where $H_{\mathrm{eff}}$ is the effective magnetic hyperfine field observed in the Mössbauer effect in ${}_{}{}^{161}{}_{}{}^{}\mathrm{Dy}$ (26-keV $\gamma$ rays) and $\mu$ is the ordered magnetic moment observed in the neutron diffraction.