Effect of additions of phosphorous, boron, and silicon on the structure and magnetic properties of the melt-spun FePd ribbons

Formation of the L1 ₀ structure in FePd alloys doped with nonmetallic elements is studied on melt-spun and annealed samples. The melt-spun Fe ₄₁ Pd ₄₁ P _18−x−y B _x Si _y (x = 0–14; y = 0, 6) ribbons were annealed at the temperatures of 400–650 °C for different holdings in the range from 5 min to several hours and studied by X-ray and thermomagnetic analysis and TEM. The saturation magnetization, Curie temperature of the L1 ₀ phase, and grain size of the melt-spun doped Fe ₄₁ Pd ₄₁ P _18−x−y B _x Si _y ribbons decrease in comparison with those of the melt-spun binary FePd alloy. The refined grain structure results in enhancing coercivity. Among all as-annealed samples, the P addition favors the amorphization of the as-spun Fe ₄₁ Pd ₄₁ P ₁₈ ribbons and refines grains of the formed L1 ₀ phase, but decreases magnetization. Substitution of B for P gives rise to magnetization of the Fe ₄₁ Pd ₄₁ P _18−x−y B _x alloys, but decreases their coercivity. A partial substitution of Si for B at the same P content refines grains and enhances the coercivity without a decrease in the magnetization of the Fe ₄₁ Pd ₄₁ P ₄ B ₈ Si ₆ alloy. It is suggested that P and B atoms occupy interstitial sites in the L1 ₀ lattice in the iron plane, weakening the exchange interaction and decreasing the Curie temperature. The additions of P, B, and Si to the FePd alloy allowed us to obtain the Fe ₄₁ Pd ₄₁ P ₄ B ₈ Si ₆ ribbons with the coercivity of 1560 Oe, which is 2.6 times higher than that of the melt-spun ribbons of the FePd alloy.