New half-metallic Y-Al-termination of the surface YCoCrAl alloy for spintronic and absorbing and spin optoelectronic devices

We investigated the surface structure of the YCoCrAl alloy, which exhibits half-metallic (HM) behaviour, using first-principles density functional theory (DFT) calculations. We evaluated the stability, electronic, and magnetic properties of both the bulk and its (0 0 1) surface. For the bulk, the spin magnetic moment (SMM) was 3.00 μβ according to the Slater-Pauling method, with complete spin polarisation (SP) observed. We calculated the energy gap (Eg) using the generalised gradient approximation (GGA) to be 0.35 eV, supporting HM behaviour and indicating mechanical stability and ductility, as confirmed by further calculations. We investigated both (0 0 1) surface terminations. We found that the Y-Al termination retained HM properties, exhibiting full SP and an integer magnetic moment. The Co-Cr termination displayed a non-integer magnetic moment, unlike the bulk. We also calculated the work function and surface energy, as these parameters are essential for predicting the behaviour of various magnetic devices. Additionally, the optical properties of both the bulk and Y-Al-terminated surfaces suggest use in absorbing and reflective coatings and spin-optoelectronic devices.