Structural, electronic and magnetic properties of weakly correlated metal Sr2CrTiO6: a first principles study

Abstract

Structural, electronic and magnetic behaviour of a less-explored material Sr₂CrTiO₆has been investigated usingabinitiocalculations with generalized gradient approximation (GGA) and GGA +Umethods, whereUis the Hubbard parameter. For each of the three possible Cr/Ti cationic arrangements in the unit cell, considered in this work, the non-magnetic band structure shows distinct traits with significant flat-band regions leading to larget_2gdensity of states around the Fermi energy. The Cr⁴⁺ion in Sr₂CrTiO₆, which is ad²system, shows a reverse splitting of thet_2gorbitals. The calculated hopping matrix contains non-zero off-diagonal elements between thed_xzandd_yzorbitals, while thed_xyorbitals remain largely unmixed. A minimal tight binding model successfully reproduces the sixt_2gbands around the Fermi energy. The Fermi surface shows a two-dimensional nesting feature for the layered arrangement of Cr and Ti atoms. Fixed spin moment studies suggest that the magnetism in this compound cannot be explained by Stoner's criterion of an itinerant band ferromagnet. In the absence of HubbardUterm, the ground state is a half-metallic ferromagnet. Calculations for the anti-ferromagnetic spin arrangement show re-arrangement of orbital character resulting in (a) narrowd_xz/d_yzbands and sharp peaks in the density of states at the Fermi energy and (b) highly dispersived_xybands with a broader density of states around the Fermi energy. The metallicity persists even with increasingUfor both the spin arrangements, thus suggesting that Sr₂CrTiO₆belongs to the class of weakly correlated metals, while the shifting of O 2pstates towards the Fermi energy withUindicates a negative charge-transfer character in Sr₂CrTiO₆.

Keywords: Wannier functions; band structure; density of states; electronic correlations; tight binding.