MAGNETIC ANISOTROPY INDUCED IN AMORPHOUS CO-BASED ALLOY BY STRESS ANNEALING AND ITS THERMAL STABILITY

摘要

Thermomechanical treatment (TMT) i.e. cooling the material under on uniaxial stress, leads to changes in magnetic properties of ferromagnetics. Induced magnetic anisotropy is considered to be the reason for these changes. The mechanism of forming the induced magnetic anisotropy is not clear yet, especially in the case of treatment above the Curie point [1]. In this paper we investigate conditions for the induced magnetic anisotropy to be formed in the process of TMT of amorphous Fe_(3)Co_(67)Cr_(3)Si_(15)B_(12) alloy, and its thermal stability. The Co-based alloy ribbons have been manufactured by quenching from the melt in air onto rotating barrel. The ribbons are 22 mkm thick, 1.1 mm wide, the Curie temperature is 160°C, the crystallisation temperature is 570°C, magnetic induction in the 800A/m field is 0.46T, saturation magneto-striction is 0.2×10~(-6). All samples have been preliminary annealed at temperature T=350°C. The thermomechanical treatment at T=150°C with unit load 1400 MPa and exposure time 49 hours does not lead to appearance of additional anisotropy. But annealing at T=180°C during 39 hours under load 1400 MPa induces the anisotropy with constant K_(u)=40 J/m~(3). The increase in annealing temperature upto 250°C under load σ=1400 Mpa (Fig.1) leads to formation of stable induced magnetic anisotropy with K_(u)=220 J/m~(3), exposure time being over 3 hours. The annealing procedure under the same load at T=350°C increases the maximal value of K_(u) upto 550 J/m~(3) and decreases the time for reaching the maximal effect to 30 min. In the case under consideration, the samples with induced anisotropy have the easy magnetisation axis perpendicular to the ribbon lenth, and the samples have very important characteristic, namely, the slope hysterasis loop (coercive force H_(c)=0.24 A/m) with constant permeability being within wide range of magnetic fields. The created magnetic properties keep existing after winding on tores with diameter over 25 mm.