X-RAY SINGLE-CRYSTAL STRUCTURE REFINEMENTS OF THE ISOTYPIC RMNSI2 (R=LA, ND) AND PRMNCU0.5GE1.5 COMPOUNDS

The crystal structures of the LaMnSi2, NdMnSi2 and PrMnCu0.5Ge1.5 comp ounds have been refined by single crystal X-ray diffraction. All three compounds crystallize in the orthorhombic LaMnSi2-type structure (Cmc m), previously denoted as the 'TbFeSi2-type'. The variation of the ato mic coordinates and interatomic distances, observed between the RMnSi2 and RMnCu0.5Ge1.5 series, well account for enhanced Cu-Ge bonds compa red to the corresponding Si-Si ones. Simultaneously, a weakening of th e Mn-Ge bonds is observed. The modifications of these chemical bonding s are correlated to drastic changes of the Mn sublattice magnetic prop erties. The variations of the manganese local environment are related to the mon or less pronounced magnetic anisotropy observed in these se ries of materials. (C) 1998 Elsevier Science S.A.