The compounds $R{\mathrm{Ni}}_2\mathrm{Mn}$ $(R=\mathrm{Tb},\mathrm{Dy},\mathrm{Ho},\mathrm{and}\mathrm{Er})$ with a ${\mathrm{MgCu}}_2$-type structure have been synthesized. The $R$ to transition metal atom ratio is confirmed to be 1:3 using the energy dispersive spectroscopy. The structural and magnetic properties have been investigated by various experimental methods. The x-ray diffraction patterns (XRD) can be well indexed with a cubic Laves cell and space group Fd3m. The refinement results of the XRD patterns show the presence of vacancies in the crystallographic structure. The ordering temperatures $T_{\mathrm{C}}$ have been derived to be 131, 94, 75, and $50\mathrm{K}$ for $R=\mathrm{Tb},\mathrm{Dy},\mathrm{Ho}\mathrm{and}\mathrm{Er}$, respectively, which are much higher than those of their corresponding $R{\mathrm{Ni}}_2$ and $R{\mathrm{Mn}}_2$ compounds. A large difference of $M\text{−}T$ curves between zero-field-cooling and field-cooling magnetization for all samples at a certain temperature range is observed in a low field, which can be understood in the terms of narrow-domain-wall pinning and a sensitive temperature dependence of coercivity.

• Received 12 April 2005

DOI:https://doi.org/10.1103/PhysRevB.73.094436