We report the effect of replacing Cu by Pd in RCu 5 (R=Pr, Nd, Sm and Eu). The parent RCu 5 compounds crystallize in the hexagonal CaCu 5-type structure. The hexagonal symmetry is retained in PrCu 4Pd and EuCu 5− x Pd x ( x=1 and 2) but the crystal structure changes to cubic AuBe 5-type in PrCu 3Pd 2, NdCu 5− x Pd x ( x=1 and 2) and SmCu 4Pd. Substitution with Pd leads to lattice expansion and modifies the magnetic behavior. While PrCu 5 is known to be a van-Vleck paramagnet with a singlet ground state, PrCu 4Pd and PrCu 3Pd 2 show ferromagnetic-like behavior at low temperatures. SmCu 4Pd orders ferromagnetically near 28 K in contrast to the antiferromagnetic nature of the parent SmCu 5. The divalent nature of the Eu ions in EuCu 5 is retained in the ternary alloys, but the Curie temperature is reduced from 57 to 24.5 and 14.5 K in EuCu 4Pd and EuCu 3Pd 2, respectively, inferred from the location of peak in the heat capacity of these two compounds. The magnetic hyperfine field at the Eu nucleus measured with 151Eu Mössbauer spectroscopy in the ternary Eu-alloys is comparable to that in EuCu 5. The magnetic behavior of NdCu 4Pd is similar to that reported in NdCu 5. The zero-field-cooled, low-field magnetization of NdCu 3Pd 2 shows a region of diamagnetic behavior roughly between 21 and 4 K, but the field-cooled response is positive.
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