SIZE DISTRIBUTION OF NI PRECIPITATES IN AG-NI ALLOYS DETERMINED BY MAXIMUM-ENTROPY ANALYSIS OF ULTRA-HIGH FIELD MAGNETIZATION CURVES

Supersaturated Ag-Ni solutions containing 10 at.% Ni are produced by electron-beam co-evaporation onto cold glass substrates. Upon annealing the Ni precipitates and coarsens. The magnetization of samples annealed to various temperatures is measured at room temperature in a vibrating sample magnetometer. Samples annealed up to 650 K show superparamagnetic behavior. The size distribution of the superparamagnetic Ni particles Is extracted from the magnetization curve by applying the Maximum Entropy method in which the magnetization is modeled as a weighted superposition of Langevin functions. When a particle-size-dependent spontaneous magnetization term is incorporated into the model, the portion of the particle size distribution below 4000 Angstrom(3) is altered significantly.