Block magnetism coupled with local distortion in the iron-based spin-ladder compound BaFe2Se3

Abstract

Magnetism in the insulating BaFe2Se3 was examined through susceptibility, specific heat, resistivity and neutron diffraction measurements. After formation of a short-range magnetic correlation, a long-range ordering was observed below TN ∼ 255 K. The transition is obscured by bulk properties. Magnetic moments ( a) are arranged to form a Fe4 ferromagnetic unit, and each Fe4 stacks antiferromagnetically. This block magnetism is of the third type among magnetic structures of ferrous materials. The magnetic ordering drives unusually large distortion via magnetoelastic coupling.

Lattice dynamics ofBaFe2X3(X=S,Se)compounds

“…Therefore, we have performed also the spin-polarized DFT calculations, assuming AFM ordering of 2x2 ferromagnetic iron blocks. [10][11][12] We find the AFM solution and opening of the gap at the Fermi level in agreement with earlier DFT calculations by Saparov et al 10 Accordingly, we attempted to calculate the phonon energies in the spinpolarized case. However, having now 48 atoms in the unit cell, this calculation turns out to be computationally too demanding.…”

“…Using data from Ref. 12 for the temperature change of the lattice constants of BaFe 2 Se 3 one can perform the corresponding analysis of the Raman mode energies temperature dependance. The best fit parameters are collected in Table III.…”

“…8 BaFe 2 Se 3 is an insulator down to the lowest measured temperature with a long-range antiferromagnetic (AFM) order with T N around 255 K and short-range AFM order at higher temperatures. [9][10][11][12] It was shown that a dominant order involves 2×2 blocks of ferromagnetically aligned four iron spins, whereas these blocks order antiferromagnetically, in the same manner as the block-AFM √ 5× The Fe-S double chain in the (010) projection. w, u, v represents Fe-Fe distances of ladder rungs (w=0.2697 nm; w * =0.2698 nm) and legs (u=0.2688 nm, v=0.2720 nm; v * =0.2643 nm).…”

Magnetism of BaFe2Se3 studied by Mössbauer spectroscopy

“…A magnetic ordering temperature was found to be at about 100 K for both compounds. This finding led to some speculations about spin fluctuation in BaFe 2 Se 3 due to the discrepancy in the magnetic ordering temperatures found by the Mössbauer spectroscopy and neutron scattering [5]. Related compound BaFe 2 Se 2 O has been investigated by Mössbauer spectroscopy as well [3].…”

“…close to the ground state [5]. The long-range magnetic order established below 255 K is characterized by presence of two spin ladders within the system and two Fe 4 blocks per chemical cell [6].…”