Influence of heat treatment on magnetostrictions of Finemet Fe73.5CU1Nb3Si3.5B9

The investigation of magnetostriction of metallic glass of the Finemet type upon structural changes has been performed on samples with different thermal history. One set of samples has been annealed for 1 h at different temperatures ranging from 573 to 873 K; another set of samples has been annealed at 823 K for different times. Measurements of saturation magnetostriction s, volume magnetostriction ω and ∂ω/∂H have been performed using direct capacitance method. Spontaneous volume magnetostriction ΔVhas been determined from dilatometric measurements and has been found to be 15 × 10 −3. For the first set of annealed samples the temperature dependence of s exhibits local maxima at 573 and 733 K, above which a steep decrease of λs by about one order of magnitude is observed. The dependence of the value of ∂ω/∂H on the annealing temperature exhibits local minima at 573 and 793 K and local maximum at 723 K. These extremes in λs and ∂ω/∂H are related to the changes in CSRO and TSRO, to relaxation processes and to internal stresses. In the latter case the magnetostriction of the samples strongly decreases after annealing even for a few minutes from the value of 24 × 10 −6 by about one order of magnitude. The quantity ∂ω/∂H follows the crystallization process, exhibiting, however, maxima at 30 and 180 min annealing time. Amorphous Finemet samples crystallized after annealing at temperatures above 753 K into nanocrystalline phase containing supersaturated solid solution α-Fe(Si), Fe3Si, (FeSi)3B, Fe2B and Fe3B.