NEUTRON-DIFFRACTION STUDY OF THE LA1-XYXMN2SI2 SOLID-SOLUTION O-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-Z)

The La1-xYxMn2Si2 compounds (0<x less than or equal to 1) have been in vestigated by powder neutron diffraction. For x<0.5, the low temperatu re magnetic structures are characterized by mixed planes where both fe rro-and antiferromagnetic components coexist while for x greater than or equal to 0.5, ferromagnetic Mn planes prevail. The in-plane ferroma gnetic component couples ferromagnetically with those of adjacent plan es for x<0.2 and antiferromagnetically for x>0.2. The La0.8Y0.2Mn2Si2 compound displays a F-AF transition as a function of the temperature. The in-plane antiferromagnetic Mn moment components are smaller than t hose measured in the corresponding germanides. These results are discu ssed and compared with previous results of the La1-xYxMn2Ge2 compounds . The Mn magnetic behaviour is consistent with bibliographic data on N MR experiments and Mossbauer spectroscopy. (C) 1998 Elsevier Science S .A.