The crystal structures and magnetic properties of TiFeSi coexisting in hexagonal and orthorhombic symmetries

The intertwisted helix framework of the chiral FeSi-type structure with the space group P2(1)3 (S.G. P2(1)3) inspired us to investigate other non-centrosymmetric compounds, particularly 111-type phases with different FeSi frameworks. Various FeSi-containing 111-type phases have been summarized according to their valence electron counts and space group. In this work we have focused on the non-centrosymmetric TiFeSi phase. The crystal structure analysis of the hexagonal Fe2P-type and the reported orthorhombic TiFeSi-type (alpha-TiFeSi) indicate a superlattice relationship exists between the two structures, which drove us to perform the total energy calculations of the hexagonal and orthorhombic models of TiFeSi. Following the theoretical predictions, a hexagonal TiFeSi phase (beta-TiFeSi) is proposed and successfully synthesized at high temperature using arc melting. The crystal structure of the high-temperature hexagonal phase was determined by powder and single crystal X-ray diffraction. After the annealing of the arc-melted samples, TiFeSi crystallizes into an orthorhombic structure with the space group Ima2. The systematic magnetic characterizations indicate ferromagnetic properties are present in the non-centrosymmetric orthorhombic alpha-TiFeSi phase with possible helical magnetic ordering at low temperatures. Moreover, to compare with the centrosymmetric cases, the electronic and magnetic properties of the antiferromagnetic TiNiSi-type MFeSi (M = Zr and Hf) compounds were also examined using both density functional theory and experimental magnetic measurements. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study discovered a new non-centrosymmetric TiFeSi phase, with a superlattice relationship between its hexagonal and orthorhombic phases, successfully synthesizing the hexagonal TiFeSi phase and performing crystal structure analysis at high temperatures. Additionally, systematic magnetic characterizations were conducted on the non-centrosymmetric orthorhombic alpha-TiFeSi phase.