Hyperfine field relaxations in the Fe-Co-B amorphous alloys

A systematic increase of the average hyperfine magnetic induction at 57Fe measured at room temperature during interrupted isothermal annealing was found to be inherent to the irreversible relaxation processes in the Fe-B based soft magnetic alloys at moderately elevated temperatures. Assuming superimposed asymptotic exponential field vs. time dependences, several processes can be distinguished, their relaxation times determined and from the Arrhenius-like log τ vs. 1/T plots average activation enthalpies estimated. Results on the Fe70Co10B20 and Fe85-xCoxB15 (x=17, 19 and 21 at.% Co) amorphous ribbons between 100 and 200deg C are compared and discussed in terms of possible stress relief, free volume annihilation and short range ordering mechanisms. (orig.)