Electron transport behaviour and soft magnetic properties of bulk amorphous Fe72Si4B20Nb4 alloy

The crystallization behaviour, electrical resistivity, magnetic and mechanical properties of as-quenched bulk amorphous Fe72Si4B20Nb4 alloy was investigated. The alloy, prepared in the form of rods by a copper mould casting technique, revealed an amorphous structure as observed from x-ray diffractometry. Differential scanning calorimetry and thermal variation of electrical resistivity measurements showed distinct glass transition temperature, Tg occurring 50–60K below the crystallization onset (TX).
Such a wide supercooled range was also attributed to the highly reduced
glass transition temperature, Trg which was in the range of 0.56–0.58 found
to be prevalent in good glass forming alloys. The alloy also showed a
non-linear decrease in stability time at different temperatures between Tg
and TX. The bulk amorphous alloy exhibited a drastic decrease in electrical
resistivity around the glass transition temperature which was attributed to
high electron propagation due to enhanced stress relaxation as result of a
decrease in viscosity. The material exhibited superior soft magnetic
properties with a coercivity value of 212 mOe, which is fairly low with
respect to reported bulk amorphous alloys. The amorphous alloy also
showed saturation induction of 12 kG and a moderate Curie temperature of
595 K. The as-quenched bulk amorphous alloy exhibited a high mechanical
hardness of 1250HV (Vickers). The superior soft magnetic properties
coupled with high mechanical hardness opens up the scope for bulk
amorphous Fe–Si–B systems with Nb incorporation.