Flat-band spin dynamics and phonon anomalies of the saw-tooth spin-chain system Fe2O(SeO3)2

Abstract

Fe 3+ S = 5/2 ions form saw-tooth like chains along the a axis of the oxo-selenite Fe2O(SeO3)2 and an onset of long-range magnetic order is observed for temperatures below TC = 105 K. This order leads to distinct fingerprints in phonon mode linewidths and energies as resolved by Raman scattering. In addition, new excitations with small linewidths emerge below T = 150 K, and are assigned to two-magnon scattering processes with the participation of flat-band and high energy magnon branches. From this a set of exchange coupling constants is estimated. The specific ratio of the saw-tooth spine-spine and spine-vertex interactions may explain the instability of the dimer quantum ground state against an incommensurate 3D magnetic order. arXiv:1901.09617v1 [cond-mat.str-el]

Magnetic structure study of the sawtooth chain antiferromagnet $$\hbox {Fe}_2\hbox {Se}_2\hbox {O}_7$$

“…The above calculation indicates that sawtooth chain antiferromagnet can possess magnons with nearly flat dispersion relation. In the Raman scattering study, some peaks were observed in the chain specific polarization at 6.8, 20.7, 64.8, and 76.9 meV 24 . The peaks have been interpreted as two magnon scattering from the nearly flat bands along the chain direction.…”

“…The Curie-Weiss fit to the temperature dependence of the magnetic susceptibility yields Weiss temperature of −200(10) K, indicating predominant antiferromagnetic interactions 25 . As the temperature is decreased below 300 K, the magnetic susceptibility deviates from the Curie-Weiss rule and shows a shoulder around 120 K 24 , 25 . The short range order should develop above the transition temperature due to the low-dimensionality in the magnetism.…”

“…The short range order should develop above the transition temperature due to the low-dimensionality in the magnetism. The antiferromagnetic order occurs at 105 K, followed by a sharp increase in the magnetic susceptibility 24 , 25 and the increase in the distribution of the hyperfine fields observed by the Fe Mössbauer spectroscopy 25 . In addition, the excitations associated with the magnetic order have been detected by the Raman scattering study 24 .…”

“…The antiferromagnetic order occurs at 105 K, followed by a sharp increase in the magnetic susceptibility 24 , 25 and the increase in the distribution of the hyperfine fields observed by the Fe Mössbauer spectroscopy 25 . In addition, the excitations associated with the magnetic order have been detected by the Raman scattering study 24 . However, it is not so clear whether can be regarded as a sawtooth chain antiferromagnet due to its complicated crystal structure.…”

Enhancement of magnetization plateaus in low-dimensional spin systems

“…From an experimental point of view, the situation remains challenging, with only a limited number of compounds being reported up to today to materialize dominant magnetic interactions in a sawtooth pattern. Prominent examples are the delafossite YCuO 2.5 [54][55][56][57], the double spin chain systems KCuCl 3 and TlCuCl 3 [19], the multiferroic Mn 2 GeO 4 [58][59][60], the olivines ZnL 2 S 4 (L = Er, Tm, Yb) [61], and the Fe chains Rb 2 Fe 2 O(AsO 4 ) 2 and Fe 2 O(SeO 3 ) 2 [62,63]. Remarkably, and despite great efforts, a magnetization plateau has not been reported for any of these systems.…”