MAGNETIC-PROPERTIES OF NDMN6GE6 AND SMMN6GE6 COMPOUNDS FROM SUSCEPTIBILITY MEASUREMENTS AND NEUTRON-DIFFRACTION STUDY

Investigations by susceptibility measurements and neutron diffraction experiments have been performed on the ternary germanides NdMn6Ge6 and SmMn6Ge6 of the YCo6Ge6-type structure (P6/mmm). This structure, closely related to the HfFe6Ge6 type, can be described as a disordered filled derivative of the CoSn B35-type structure. The Mn atoms build Kagome layers stacked along the c axis, in between which the rare earth atoms are randomly distributed. Owing to the Mn atom coordination of the rare earth, this structure appears closely related to the CaCu5- and ThMn12-type structures. NdMn6Ge6 and SmMn6Ge6 are ferromagnetic below-417 and 441 K respectively. At 35 K a second magnetic transition related to a spin reorientation process takes place in NdMn6Ge6. Neutron diffraction study of NdMn6Ge6 confirms that both the rare earth and Mn sublattices order simultaneously above room temperature. In the whole temperature range 2-300 K NdMn6Ge6 is a collinear ferromagnet (i.e. positive Nd-Mn interaction). In the temperature range 300-35 K the moment direction deviates by Phi approximate to 40 degrees from the c axis, whereas an easy plane occurs at 2 K (mu(Nd)=2.87(43) mu(B) and mu(Mn)=2.26(14) mu(B)) The results are discussed and compared with those previously obtained for the parent YMn6Ge6, GdMn6Ge6 and RMn(6)Sn(6) (R=Tb-Er, Lu) compounds.