Activation Energies of Crystallization in Amorphous $RMn_{4.5}Ge_{4.5}Fe_{1.5}Al_{1.5}$ (R = La, Y, Dy) Alloys

The effective activation energies, characteristic crystallization temperatures and enthalpies of amorphous $RMn_{4.5}Ge_{4.5}Fe_{1.5}Al_{1.5}$ (R = Y, La, Dy) alloys produced using melt-spinning technique were investigated by differential scanning calorimetry. X-ray diffraction measurements were performed for as-quenched and annealed samples. The crystalline structure of annealed $YMn_{4.5}Ge_{4.5}Fe_{1.5}Al_{1.5}$ and $DyMn_{4.5}Ge_{4.5}Fe_{1.5}Al_{1.5}$ alloys was determined as orthorhombic $TbFe_6Sn_6$-type with Cmcm (63) space group. The alloy with Y appears as a more useful non-magnetic analogue for $DyMn_{4.5}Ge_{4.5}Fe_{1.5}Al_{1.5}$ than the La-based alloy. The differential scanning calorimetry curves for Dy- and Y-based alloys also exhibit similar thermal behavior. The effective activation energies $E_a$ were determined using the Kissinger approach and high values up to 778±74 kJ/mol for La-based sample were established. The comparison of Y-, La-, and Dy-based alloys suggests improvement of thermal stability with the increase in rare-earth element atomic radius in the glassy $RMn_{4.5}Ge_{4.5}Fe_{1.5}Al_{1.5}$ systems.