B. —DISORDERED METALLIC ALLOYS. MAGNETISM IN DISORDERED METALLIC SYSTEMS : THE LOCAL ENVIRONMENT EFFECTS.INHOMOGENEOUS CHARACTER OF THE TRANSITION NON MAGNETISM-MAGNETISM IN ALLOYS THROUGH MAGNETIC MEASUREMENTS

Magnetic measurements allow a detailed study of the transition from non-magnetism to magnetism of an alloy. The study of alloys in which this transition occurs for low concentrations allows the deduction of a simple model relating the behavior of an impurity with neighbouring impurities. For alloys in which the transition occurs in a higher concentration range, a model can no longer be deduced from the simple analysis of experimental results. The extension of the model found for dilute alloys allows a good understanding of the main characteristic phenomena of concentrated alloys (particularly the superparamagnetism of giant moments). Polarization effects of passive sites by active ones, clearly shown on ternary alloys, provide a more detailed model of the behavior of alloys in the transition range.