Effect of substitution of 3d, 4d and 5d elements on structural, electronic, magnetic properties and XMCD spectra of Co-based full Heusler alloys: A DFT study

Abstract

In the present work, we have probed the role of substitution of 3d, 4d and 5d elements (i.e., with electronic configuration (EC): ndy, where n = 3–5; y = number of electrons in the d level) at the B site on structural, magnetic and electronic properties of a set of full Heusler alloys (FHAs) namely, Co2BAl, using density functional theory (DFT) based electronic structure (ES) calculations. We have optimized all the 30 combinations studied here in Fm3̄m (A2BC type, conventional FHA structure) and F4̄3m (ABAC type, inverse FHA structure) space groups using VASP code. Thereafter, ES calculations have been carried out using DFT based FPLAPW method as implemented in WIEN2k code with an exchange-correlation term (PBE + mBJ + SOC), which is beyond GGA and includes the spin-orbit-coupling (SOC). Furthermore, XMCD calculations have been performed using single particle approximation and Fermi’s Golden rule as implemented in WIEN2k code. FHAs with atoms having EC nd1−6,10 (n = 3–5) at B site have Fm3̄m as the lowest energy structure with the exception of 4d6 and 5d6. Calculated magnetic moments (MM) of these alloys with atoms with EC nd1−5 are found to be in agreement with the Slater-Pauling (SP) rule, with an integer or close to integer value along with 3d6. However, alloys having atoms at B site with nd7−9 (along with 4d6 and 5d6) are found to be in F4̄3m space group and their values of the MM are not in agreement with the SP rule. XMCD spectra corresponding to various atomic sites help in understanding the impact of the local environment. Hence, calculations of the same have been performed to understand the low values of Co MM with atoms at B site having EC 3d3−5 and the negative MM of the Ti and Zr atoms at B site.