Microstructure and magnetic properties of Gd-Hf-Co-Al glassy alloys by liquid-liquid phase separation

Phase separated glassy ribbons were prepared in the Gd-Hf-Co-Al system by rapid quenching of the melt. From the Gd55Co25Al20 ternary good glass former, we substitute Gd with Hf by 10, 20, 27.5, 35, 45 and 55 at. %. Due to the strong positive enthalpy of mixing between the principal elements Gd and Hf (ΔHmix = +11kJ/mole) a heterogeneous microstructure is formed consisting of two amorphous phases Gd-enriched and Hf-enriched. For the alloys with clearly phase separated microstructure, nano-meter scale (100nm) secondary phase separation is observed in each amorphous phase. In the case of the Gd27.5Hf27.5Co25Al20 alloy, coexistence of two different types of microstructure such as a droplet-like and interconnected structure were observed from the areas having different cooling rate. This microstructure evolution is in good agreement with calculation results by Lattice Boltzmann method. On the other hand, measured magnetic properties show the composition and volume fraction dependence of magnetization and transition temperature (Tc) of Gd-Hf-Co-Al system. The saturation magnetization decreases as a function of Hf contents and can be described by a simple mixture model.