Magnetic properties and structure of the Fe63.5Mn10Cu1Nb3Si13.5B9 alloy nanocrystallized under tensile stresses

Abstract

The influence of introduction of 10 at. % Mn for Fe in the classical Finemet (Fe73.5Cu1Nb3Si13.5B9) on its magnetic properties, magnetic anisotropy, and structure is studied after nanocrystallization annealing at 520°C with varying duration from 10 min to 4 h in the presence of tensile stresses (σ = 200 MPa) (SA) and without them (NA). It is established that in the Fe63.5Mn10Cu1Nb3Si13.5B9 alloy (Mn10-alloy), just as in the classical Finemet, SA results in the induction of transverse magnetic anisotropy, yet, the constant of induced magnetic anisotropy is decreased by a factor of 4. The coercivity of the Mn10-alloy grows with increasing annealing time upon both SA and NA, while that of Finemet virtually does not change. Unlike Finemet, in the Mn10-alloy, along with the α-Fe(Si, Mn) solid solution and Fe3Si phase, there form borides already after 10-min treatment. This results in the change in the volume fractions of structure components with a negative magnetostriction, α-Fe(Si, Mn) and Fe3Si, which are responsible for the induction of transverse magnetic anisotropy, and positive magnetostriction, FeB, Fe2B, Fe3B, and hence, most likely, causes decrease in the constant of IMA of the Mn10-alloy. Besides, unlike Finemet, the average grain size in the alloy with Mn increases with the time of annealing, which, together with the formation of borides, increases the coercivity.