Phase Evolution in Manganese-Germanium System During Mechanical Alloying

Abstract

In this thesis work, the phase evolution during the synthesis of metastable binary germanides of Mn-Ge system was investigated. A thorough literature review on the various metallic germanides was performed. Attempts were made to synthesize various metastable manganese germanides by mechanical alloying. The phase evolution during the synthesis was investigated by x-ray diffraction and scanning electron microscopy. Powders of MnGe (an equiatomic metastable phase of Mn-Ge system) were successfully synthesized. The structural characterization revealed the lattice parameter and the particle size to be 0.4798 ± 0.0008 nm and ~1-3 μm, respectively. The magnetic characterization showed that MnGe was paramagnetic at room temperature, antiferromagnetic at sub-ambient temperatures with Neel temperature estimated as ~162 K, and the magnetization (at 1 Tesla) was estimated to be ~ 3 emu/g. In the case of MnGe, based on the phase evolution, attempts were made to reduce the synthesis time by varying appropriate processing parameters. During the synthesis of Ge-rich metastable manganese-germanides, the evolution of the respective phases (Mn3Ge5, MnGe2, and MnGe4) was always accompanied with MnGe. The metastable MnGe synthesized (in powder form), in this work, at ambient temperature and pressure conditions had a considerably high yield and reproducibility, unlike in the past synthesized by high-pressure/high-temperature technique (in bulk form) and thin-film deposition technique (thin film) available in the literature. Future study would involve the synthesis of other metastable compound by isolating MnGe during their evolution.