Magnetic Tb₇₅Fe₂₅ Nanoglass for Cryogenic Permanent Magnet Undulator

In this paper, the magnetic properties of a nanostructured amorphous Tb75Fe25 material, which is termed as nanoglass (NG), are reported. The nanoglass structure consists of two regions: a nanometer-sized glassy core (10–20 nm) and nanometers of glass–glass interfaces (∼1–2 nm). The nanoglass was prepared by inert gas condensation technique. The amorphous phase of this specific alloy composition is otherwise not synthesized by conventional rapid quenching techniques. The as-prepared NG was further treated by high-pressure torsion (HPT) to introduce deformation in the material. The Curie temperature was found to be around 200 K for the as-prepared and HPT-treated samples. The magnetic coercivity for the as-prepared and HPT samples was found to be about 4 T at 1.8 K. Furthermore, heat treatment of these two samples at 390 °C for 30 min was performed, which resulted in the crystallization of the amorphous alloys. X-ray diffraction patterns and Rietveld refinement reveal that cubic Fe2Tb and hexagonal Tb phases formed after heat treatment. It is substantiated that the high contents of Fe2Tb and Tb crystalline phases were precipitated after heat treatment for the HPT sample compared to the NG sample. There was no any pronounced texture effect observed after heat treatment in both cases. However, the coercivity of these samples decreased upon crystallization. The heat-treated sample subjected to HPT was noted to have higher magnetization than the heat-treated NG. The above reported high coercivity (4 T) at 1.8 K could make the sample a suitable material for the application of cryogenic permanent magnet undulators (CPMUs).