Influence of heating temperature on Nd-Sr-Mn-O manganites synthesised via thermal treatment and sol-gel method

Mixed-valence manganites have garnered significant interest owing to their intriguing colossal magnetoresistance effect. In the realm of manganites, the primary challenge is achieving remarkable magnetoresistance (MR) values even with weak magnetic fields, rendering these materials applicable for the utilisation of magnetic sensors near room temperatures. The selection of preparation methods and synthesis routes is crucial as it can alter the grain size formation and/or distribution, subsequently affecting the magnetic and electrical behaviour of manganite materials. In this project, a newly developed approach known as the thermal treatment method (TT) was employed to synthesise Nd0.7Sr0.3MnO3 (NSMO) manganites. Given the novelty of this approach, optimisation and fine-tuning of heat treatment parameters are imperative to achieve the utmost desirable physical properties. The first part of this investigation focuses on assessing the impact of calcination temperatures on the NSMO samples. Higher crystallinity was achieved when NSMO was calcined at 500 °C and 900 °C. However, an unfavorable morphology was observed in sample calcined at 900 °C and sintered at 1200 °C. Besides, the NSMO samples exhibited distinct magnetic phase transition when calcined at 500 °C. Regarding magneto-transport behaviour, the intrinsic MR is more predominant in the sample calcined at 500 °C and sintered at 1200 °C. Thus, it can be deduced that 500 °C is the optimum calcination temperature. The next part of this thesis aims to explore the grain size effect on the NSMO samples synthesised via thermal treatment and sol-gel (SG) methods at various sintering temperatures (700 °C to 1200 °C). While the sol-gel method yielded a single NSMO phase, minor phases were detected in the NSMO samples prepared using the thermal treatment method at a lower sintering temperature. XRD result indicated larger crystallite size formation and better crystallinity in SG, but SEM analysis revealed a greater variation of grain size in TT. Additionally, TT exhibited a broader magnetic phase transition due to the existence of nonferromagnetic clusters resulting from the detected minor phases. In both series of samples, the presence of MR peaks suggests the prevalence of intrinsic MR, with peak intensity increasing as the sintering temperature rises. Interestingly, contrary to prior research, the intrinsic MR is more dominant in SG samples with smaller grain sizes, which can be attributed to the microstructure change and morphology variations. In conclusion, this study highlights the significance of structural and microstructural formation resulting from various synthesis methods in governing the physical properties of manganite samples. This study stands out as the pioneer in preparing Nd-based manganites using the thermal treatment method. It offers the advantages of being cost-effective and environmentally friendly, while also featuring a simplified preparation method for manganites.

Text 118749.pdf Download (1MB) Official URL or Download Paper: http://ethesis.upm.edu.my/id/eprint/18409

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