Half‐Metallicity in Quaternary Heusler Alloys with 3d and 4d Elements: Observations and Insights from DFT Calculations

Abstract

In this work, important insights into the evolution of half‐metallicity in quaternary Heusler alloys are provided. Employing ab initio electronic structure methods we study 18 quaternary Heusler compounds having the chemical formula CoX′Y′Al, where Y′ = Mn, Fe; and X′ a 4d element. Along with the search for new materials for spintronics applications, the trends in structural, electronic, magnetic properties, and Curie temperature are investigated. Comparative studies with the compounds in the quaternary series CoX′Y′Si with X′ materials from the 3d and 4d transition metal series in the periodic table have been made. We observe that the half‐metallic behavior depends primarily on the crystal structure type based on atomic arrangements and the number of valence electrons. As long as these two are identical, the electronic structures and the magnetic exchange interactions bear close resemblances. Consequently, the materials exhibit identical electronic properties, by and large. The roles of different transition metal atoms in affecting the hybridizations and their correlations with the above observations are analyzed. This work, therefore, provides important perspectives regarding the underlying physics of half‐metallic behavior in quaternary Heusler compounds which goes beyond specifics of a given material. This, thus, paves the way for smart prediction of new half‐metals. This work also figures out an open problem of understanding how different ternary Heuslers with different electronic behavior may lead to half‐metallic behavior in quaternary Heuslers with 4d transition metal elements.