Anisotropic thermal expansion of as-cast RQM ribbons and magnetic anisotropy

Abstract

Less expansion and more shrinkage along the ribbon axis than transverse to the axis is generally observed during temperature cycle when the dilatation of as-cast ribbons is measured. This anisotropy is seen to relax together with modest as-cast magnetic anisotropy if the sample has been cycled up to ∼400°C prior to the test. Often but not always, the as-cast magnetic anisotropy shows the sign as expected after tensile stress annealing. During ribbon solidification, tensile stress can create anelastic strain or even structural anisotropy which results in both the observed anisotropies. Ribbons quenched on air are known to bear some macroscopic heterogeneity which acts by forces between surfaces and ribbon interior. These forces could interfere with the relaxation of the as-cast anisotropies. Tests show that the interference is weak and the heterogeneity acts isotropic in the ribbon plane and induces magnetic anisotropy of its own.