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Polycrystalline samples of R 3 Pd 4 Ge 4 (R=Tb and Er) intermetallics were studied with magnetometric and neutron diffraction methods. Both compounds crystallize in the orthorhombic Gd 3 Cu 4 Ge 4 -type structure, in which the rare-earth atoms occupy two inequivalent crystallographic positions. Both compounds order antiferromagnetically below their Neel temperatures of 13 K in the case of Tb 3 Pd 4 Ge 4 and of 4 K in the case of Er 3 Pd 4 Ge 4 . These transition temperatures were confirmed in magnetic measurements. The magnetic structures were studied with the support of group theoretical considerations. For R=Tb both sites order simultaneously and the magnetic ordering is described by two propagation vectors. One of them is k 1 =(0, 0, 0) describing the ordering in the 4e sites, whereas the second vector k 2 =(0, 0.212(1), 0.788(1)) describes the ordering in both 2d and 4e sites. In the case of the Er compound the magnetic structure is also described by two propagation vectors: k 1 =(0, 0, 0) which describes the ordering in the 4e sites and k 2 =(0, 0.174(1), 0) describing the ordering in the 2d sites. |
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