Magnetic ordering of Pr6F13Si and Nd6Fe13Au studied by neutron diffraction

The magnetic structure of the compounds Pr6Fe13Si and Nd6Fe13Au has been studied by powder neutron diffraction. The magnetic structures are very similar, revealing the same collinear antiferromagnetic ordering of the Fe (four) and the R (two) sublattices associated with the wavevector q = (001) and an I-P type magnetic lattice with anticentring translation. The moments of all sublattices located in (xyo) layers and sandwiched between successive Si (Au) layers perpendicular to z at z = -0.25, 0.25, are confined to the same direction within the (xyo) plane. They change their direction collectively when going to the next Au (Si) layers at z = 0.25, 0.75, thus producing antiferromagnetic ordering within all eight sublattices. At 1.5 K, the rare earth moments in Nd6Fe13Au are equal to 3.4(2) mu(B) for Nd1 and 2.5(1) mu(B) for Nd2. In Pr6Fe13Si the two Pr sites have almost the same moment of 2.8(1) mu(B) at 1.5 K. The average ordered Fe moment value is lower in Pr6Fe13Si (1.57 mu(B)/Fe atom) than in Nd6Fe13Au (2.3 mu B/Fe atom).