Microstructure and magnetic properties of Gd–Hf–Co–Al phase separated metallic glasses

Microstructure and magnetic properties of phase separating Gd55−xHfxCo25Al20 metallic glasses are investigated for x = 0, 10, 20, 27.5, 35, 45 and 55 at. %. The Gd–Hf–Co–Al alloy system undergoes typical liquid–liquid phase separation during quenching and decomposes into Gd-rich and Hf-rich amorphous phases. The microstructural features such as length scale and volume fraction of separated phases and the occurrence of secondary precipitation strongly depend on composition and cooling rate. In particular for the Gd27.5Hf27.5Co25Al20 alloy, a strong dependence of microstructural features on the local cooling rate could be observed. The Gd-containing alloys exhibit soft magnetic behavior (Hc < 100 Oe) and a magnetic transition from paramagnetic to ferromagnetic in the temperature range 75–115 K, whereas the Hf55Co25Al20 remains paramagnetic. Investigations of magnetic properties of phase separated Gd–Hf–Co–Al glasses reveal that the saturation magnetization depends on the overall amount of Gd atoms in the sample and is not remarkably affected by phase separation processes. The results indicated that the magnetic transition originated predominantly from the Gd-rich phase.