Structure and magnetic properties of Fe-Ga alloys doped by Tb

Abstract

The dependence of magnetostriction and magnetic properties in Fe-19Ga-xTb (x = 0–0.37 at. %) and Fe-27.4Ga-xTb (x = 0–0.5 at. %) alloys on the concentration of Tb has been analyzed. A phase enriched in Ga and Tb (up to 7 at. % Tb and 41 at. % Ga) was observed at the grain boundaries and inside the interdendritic regions after direct solidification. Microstructure analysis shows a two-phase (D03 and Tb + Ga-rich phase) structure in Fe-19Ga-Tb and a three-phase (D03, L12 and Tb + Ga-rich phase) structure in Fe-27Ga-Tb-type alloys. The chemical compositions of all phases have been analysed quantitatively and the solubility limit of Tb in Fe-Ga was evaluated to be less than 0.15 at. %.The addition of Tb increases the saturation magnetostriction in the Fe-19Ga-xTb and Fe-27.4Ga-xTb alloys (up to ≈235 ppm for the Fe-19Ga-0.37 Tb and ≈240 ppm for the Fe-27.4Ga-0.3 Tb samples). These values are considerably higher than those of the binary counterparts. The magnetic permeability, μ, and magnetocrystalline anisotropy constant, K1, are increased by the addition of Tb, too, from 3.94 × 10−4 H/m and 1.28 × 104 J/m3 for the Fe-19 Ga alloy to 4.62 × 10−4 H/m and 1.316 × 104 J/m3 for the alloy containing 0.37 at. % Tb.The reversible order – disorder phase transition of the type D03 ↔ A2 leads to a transient anelastic effect at about 555 °C and 520 °C respectively upon heating and cooling of the Fe-19 Ga-0.15 Tb alloy. Vibrating sample magnetometry results are in a good agreement with the internal friction measurements, demonstrating the occurrence of an ordering reaction at 510 °C during cooling.