Amorphous magnetic alloys near critical concentration: Low field reversible dc magnetization

Measurements of the reversible magnetization at low dc fields have been used to investigate the magnetic response near the multicritical point (x_c) of two sets of amorphous alloys. In both cases, the ferromagnetic (FM) to spin glass (SG) transition line is found to be non-monotonic. The collapse of the magnetization as x→x⁺_c and the rapid increase in the susceptibility as x→x^-_c are suggestive of a percolation transition in the magnetic network at x=x_c. From a study of the non-linear susceptibility in the most concentrated spin glass alloy in each system, we obtain scaling exponents in agreement with previous reports providing further support for a thermodynamic phase transition at the spin glass temperature. For the first time we find a divergence in the linear susceptibility in these samples similar to that expected for the non-linear susceptibility and attribute it to their proximity to the FM phase. Dramatic changes in the transition temperatures and a perceptible shift in x_c are observed when normal boron is replaced by enriched boron (≈100%¹¹B) in one series of alloys.