First principles study of phase stability, electronic structure and magnetism in Mn2YZ systems with multiple functionalities

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Heusler compounds are a remarkable class of intermetallics which possess many functionalities including magnetic shape memory effect(MSME), half-metallicity, magnetocaloric effect and magnetoresistance with many possible applications. In the family of Heusler compounds, Mn2YZ compounds have attracted considerable attention due to their interesting structure-magnetism relations leading to applications in magnetomechanical devices, magnetic sensors, spintronics, and energy technology. In this thesis, weinvestigate the phase stability, structural, electronic, elastic and magnetic properties of several Mn2YZ systems from first-principles electronic structure calculations. The primary motivation is to explore and understand the possibility of martensitic phase transformation leading to magnetic shape memory effect and its origin in several pristine and substituted Mn2YZ systems. In this thesis we investigate Mn2NiGa, Fe and Co substituted Mn2NiGa, Mn2FeGa and Mn2Ni1+xSn1−x compounds. The choice of the systems is motivated by the interesting experimental results obtained in each case. A complete picture of martensitic phases and the path of phase transformation in magnetic shape memory alloy Mn2NiGa is explained from the electronic structure, phonon dispersion, and electronic susceptibility. The effect of Fe and Co substitution on the martensitic phase transformation, mechanical stability, magnetization and the magnetic ordering temperature of Mn2NiGa is investigated extensively, leading to establishing several important differences in physical properties with well known magnetic shape memory system Ni2MnGa.
Supervisor: Subhradip Ghosh