Thermal stability and magnetic properties of Fe–Co–M–Zr–Nb–Ge–B (M=Mo, Cr) bulk metallic glasses

Fe62Co8−xMxZr6Nb4Ge1B19 (M=Mo, Cr) bulk metallic glasses were synthesized in the diameter range up to 2 mm by copper mold casting, which exhibit high thermal stability and large glass-forming ability. The super-cooled liquid region diminishes by the dissolution of Mo. The addition of 2 at% Cr leads to the broading of the liquid region remarkably, resulting in the improvement of thermal stability. The crystallization takes place through a single exothermic reaction, accompanying the precipitation of more than three kinds of crystallized phases such as α-Fe, Fe2Zr and ZrB2. The Fe-based alloys show soft ferromagnetic properties. The saturation magnetization (σs) decreases with increasing Mo or Cr content while the saturated magnetostriction increases with raising Mo or Cr content. There is no evident change in the σs and coercive force (Hc) with annealing temperature below the crystallization temperature, which suggests a more relaxed atomic configuration the glasses have. The crystallization causes a substantial enhancement in both σs and Hc. Each soft magnetic property of the glasses containing Cr with higher thermal stability is superior to that of the alloys containing Mo.