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

In the present work, we have probed the role of substitution of 3d, 4d and 5d elements (i.e., with electronic configuration (EC): nd(y), 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 Fm3m (A(2)BC type, conventional FHA structure) and F43m (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 nd(1-6,10) (n = 3-5) at B site have Fm3m as the lowest energy structure with the exception of 4d(6) and 5d(6). Calculated magnetic moments (MM) of these alloys with atoms with EC nd(1-5) are found to be in agreement with the Slater-Pauling (SP) rule, with an integer or close to integer value along with 3d(6). However, alloys having atoms at B site with nd(7-9) (along with 4d(6) and 5d(6)) are found to be in F43m 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 3d(3-5) and the negative MM of the Ti and Zr atoms at B site.