Effect of Gd on the devitrification and magnetic properties of [(Fe0.6Co0.4)0.75Si0.05B0.20]96-xNb4Gdx metallic glasses

The influence of microalloying with Gd on the thermal stability, crystallization and magnetic properties of [Fe_0.6Co_0.4)_0.75Si_0.05B_0.20]_96-xNb₄Gd_x (x=0,1,2,5) metallic glasses was examined. Various glass-forming ability criteria were calculated based on thermal characteristics obtained by differential scanning calorimetry for melt-spun ribbons and compared to the maximum size achieved of the alloys via direct rod casting. Although thermodynamic-based criteria predict larger glass-forming ability for the alloy with higher Gd content, x=5 alloy showed the lowest ability to form full glassy rods. The structural evolution after first crystallization event was analyzed by x-ray diffraction and Transmission Mössbauer spectroscopy. The observed changes in the precipitated phases in x=5 alloy compared to x=0,1,2 alloys are associated to the decrease in the glass-forming ability. The formation of phases other than (FeCo)₂₃B₆ phase in x=5 alloy is responsible for not achieving fully glassy rods. Additionally, the magnetic properties of glassy ribbons are significantly affected by the addition of Gd. Saturation magnetization and Curie temperature decrease as Gd content increases.