Thermodynamic and kinetic insights into the origin of spin-gapless semiconducting behavior in Ti2CoSi Heusler compound

In this study, the origin of spin-gapless semiconducting behavior in Ti2CoSi was theoretically revealed. It was discovered that Ti2CoSi is stable in Cu2MnAl-type structure at the ground state. However, the Hg2CuTi-type structure is thermodynamically preferred in Ti2CoSi at high temperatures, which is responsible for the experimentally observed spin-gapless semiconducting behavior. Comparative analysis of data revealed that the kinetic arrest of atomic diffusion, caused by the rapid-cooling method, led to the formation of a Ti2CoSi phase with a structure similar to the Hg2CuTi-type in thin film samples. This study proposed that the physical properties and applications of Heusler compounds in devices are closely dependent on their structure, which can be adjusted by carefully controlling the thermodynamic states and kinetic process during sample fabrication. The calculation results indicate that the style and strength of interatomic chemical bonds are the inherent factors that aid in determining the phase stability in solids. These results not only suggest that thermodynamic states and kinetic processes during the sample preparation determine the spin-gapless semiconductor characteristic in Ti2CoSi but also are helpful in designing and exploring magnetic functional materials for technological applications.