Neutron-diffraction study in TlFeS2 and TlFeSe2 at low temperatures

Abstract

The crystal and magnetic structures of TlFeS 2 and TlFeSe 2 are studied by neutron diffraction in the temperature range of 10-320 K. The structures of TlFeS 2 and TlFeSe 2 have monoclinic symmetry with the space group C2/m at room temperature. TlFeS 2 displays an antiferromagnetic phase at temperature below 200 K. The antiferromagnetic phase transition in TlFeSe 2 takes place at a temperature below 290 K. The tem perature dependence of the unit cell parameters and volume are obtained. The coefficients of thermal and linear expansion are calculated. The temperature dependences of the interatomic distances are presented.

Spin dynamics of the spin chain antiferromagnet RbFeS$_2$

“…1 (a) [12][13][14] . As previously reported, KFeS 2 , RbFeS 2 , KFeSe 2 , and RbFeSe 2 crystallize in the monoclinic space group C/2c, while TlFeS 2 and TlFeSe 2 crystallize in the monoclinic space group C/2m [15][16][17] . CsFeS 2 is somewhat different, crystallizing in an orthorhombic space group and undergoing a structural transition from Immm to P 1 upon cooling 14,18,19 .…”

High-pressure effect on the chain-like crystal structure of the semiconductors TlFeSe2 and TlFeS2

“…The obtained structural parameters are well agreed with the previous results. 4,5,14 In whole pressure range in experiments, the monoclinic phase of both investigated compounds remains unchanged. The pressure dependencies of lattice parameters of TlFeSe 2 and TlFeS 2 are shown in Fig.…”

“…4,5,11,14,15 The crystal structure of these compounds is characterized by the short intrachain Fe-Fe distance of about 2.7Å, as compared with the Fe-Fe distance of 2.48Å in the BBC iron metal, which is much smaller than the Fe-Fe interchain distance of about 7Å. 4,5,11 Hence, the exchange magnetic interaction between the iron ions along a chain is much stronger than the interchain magnetic interaction, mediated via Fe-X-Tl-X-Fe superexchange, which leads to reveal a quasi-one-dimensional magnetic character in these compounds.…”

“…On the other hand, the weak interchain superexchange interaction gives rise to the phase transition from one-dimensional to collinear three-dimensional antiferromagnetic order at the Néel temperatures of 290 K (TlFeSe 2 ) and 196 K (TlFeS 2 ). 4,5,11,14 The small Fe-Fe intrachain separation can give rise to the strong Fe-Fe covalency and 3d charge-carrier delocalization in the chains, resulting in the small ordered Fe 3+ moments of the order of 2 µ B far below the ionic value of 5 µ B . 4,5 Minor structural variation can lead to a remarkable change on their magnetic properties.…”

Structural, electronic and magnetic properties of TlFeSe2 under high pressure

“…For all calculations, projector-augmented plane wave (PAW) based on the spin-polarized density functional theory is used as implemented in vienna ab initio simulation package (VASP). [22] Since the magnetic properties of TlFeSe 2 are susceptible to its micro-structure as previous neutron diffraction studies manifested [3,23], it is important to pick out an appropriate method to reproduce both lattice parameters and magnetic properties accurately. Although Perdew-Burke-Ernzerhof (PBE) version of the generalized gradient approximation is applicable to most cases owing to the reduction of chronic overbinding of the local spin density approximation, [24,25] it usually slightly overcorrects equilibrium properties which are related to equilibrium lattice constants [26].…”