Thermal stability and soft magnetic properties of Fe-Nb-B amorphous alloyswith high boron concentrations

Ferromagnetic amorphous Fe-Nb-B alloys containing 30 at%B were found to exh ibit a large supercooled liquid region with a temperature interval over 50 K before crystallization and the largest Delta T-x(=T-x-T-g) reaches 71 K f or Fe62Nb8B30. The Delta T-x is strongly dependent on B content, while the soft magnetic properties of saturated magnetization (I-s), permeability (mu (e)) and saturated magnetostriction (lambda(s)) are dependent on Nb content . The Fe62Nb8B30 amorphous alloy exhibits good soft magnetic properties of 0.68 T for I-s, 2.6 A/m for coercive force (H-c), 19300 for mu(e) at 1 kHz and 7.7 x 10(-6) for lambda(s). The crystallization takes place through a s ingle exothermic reaction, accompanying the simultaneous precipitation of t he three crystalline phases of alpha-Fe, Fe2B and FeNb2B2. The crystallizat ion mode which requires long-range atomic rearrangements plays a dominant r ole in achieving the high stability of the supercooled liquid against cryst allization.