Crystal Structure and Magnetic Properties of RCu4Ag (R = Rare Earth) Intermetallic Compounds

The ${\mathrm{RCu}}_5$ intermetallic compounds crystallize either in the cubic ${\mathrm{AuBe}}_5$ type structure or in the hexagonal ${\mathrm{CaCu}}_5$ structure depending upon the particular rare earth ion involved. The effect of substituting Ag for one Cu on the structure stability of ${\mathrm{RCu}}_5$ compounds has been investigated. It is observed that the compounds ${\mathrm{RCu}}_4\mathrm{Ag}\mathrm{\hspace{0.17em}(}\mathrm{R}\mathrm{\hspace{0.17em}=\hspace{0.17em}}\mathrm{Nd}\hspace{0.17em}\mathrm{to}\hspace{0.17em}\mathrm{Tm})$ crystallize in the ${\mathrm{AuBe}}_5$ type structure. The magnetization of these compounds with $\mathrm{R}\mathrm{\hspace{0.17em}=\hspace{0.17em}}\mathrm{Nd}$ to Ho has been studied in temperature range 4.2 to 300 K and in magnetic fields up to 21 kOe. The compounds with $\mathrm{Nd}$ , Sm, Gd and Tb are found to order antiferromagnetically with Néel temperature of 7, 7, 9 and 16.5 K, respectively. The Dy and Ho compounds exhibit ferromagnetic behavior in magnetic fields larger than about 1 kOe. In the paramagnetic region, the magnetic susceptibility of all the compounds except that of ${\mathrm{SmCu}}_4\mathrm{Ag}$ follows the Curie‐Weiss law. The paramagnetic Curie temperatures of these compounds can be explained on the basis of RKKY theory with a suitable choice of the Fermi wave vector.