THE MAGNETIC PHASE-DIAGRAM OF GDXY1-XMN6GE6

The magnetic phase diagrams of GdXY1-XMn6Ge6 for 0 less than or equal to X less than or equal to 1 have been deduced from magnetisation meas urements of powder samples. The macroscopic magnetisation data has bee n correlated with the local information obtained from Ge-73 NMR. In or der to derive a simplifying picture of the complex magnetic properties , analysis of the temperature dependence of the magnetisation in terms of a molecular-field approximation with interactions between localise d Gd-Gd, Gd-Mn and Mn-Mn moments has been performed. Allowing for coup ling constants varying with temperature, even the unusual temperature dependence of YMn6Ge6 magnetisation could be described sucessfully. (C ) 1998 Elsevier Science B.V. All rights reserved.