Metal–Insulator Transition Induced by Spin Reorientation in Fe₇Se₈ Grain Boundaries

Abstract

FeSe exists as a hexagonal NiAs-like crystal structure with a large number of ordered intrinsic vacancies. It is an ideal candidate for studying the effect of defects on properties such as magnetism and electrical transport. In this work, highly crystalline FeSe with the 3c crystal structure was synthesized by a solid-state reaction. Sharp changes in the magnetization at 100 K confirm a rotation of the spins from the ab plane to the c axis with decreasing temperature. We observe an interesting metal-insulator transition at the same temperature as the spin-direction changes. We propose that locked spins in the grain boundaries induce electron localization and result in the metal-insulator transition. Electron localization is confirmed by X-ray photoelectron spectroscopy of the Fe 2p peaks, which exhibit two characteristic satellite peaks. This mechanism is also verified by comparing it with the properties of the 4c-FeSe crystal structure.

Magnetic investigation of low temperature phase transition in iron selenides

“…Vacancies can strongly change material properties, which is important for producing lithium-ion batteries, solar cell units, photocatalytical agents etc [1,2]. As it was previously found out in our work [3], Fe 7 Se 8 with 3c superstructure shows a special behaviour in electrical resistivity in a temperature range from 30 to 100K, which leads to a metal-insulator phase transition. It occurs because vacancies are ordered in the selenide structure.…”

In Situ Induction of Strain in Iron Phosphide (FeP2) Catalyst for Enhanced Hydroxide Adsorption and Water Oxidation

“…Considering that the structure of FeP 2 can be described as Fe‐centered octahedra and exhibiting diamagnetism at room temperature, we conclude that Fe takes the low‐spin d 6 configuration with a valence state of 2+ . The higher binding energy peaks located at around 709.7 and 711.5 eV corresponding to Fe oxide species such as Fe 2+ and Fe 3+ resulting from the surface oxidation of strained FeP 2 …”

Study of the Phase-Evolution Mechanism of an Fe–Se System at the Nanoscale: Optimization of Synthesis Conditions for the Isolation of Pure Phases and Their Controlled Growth

“…The peaks detected at higher BEs can be assigned to charge-transfer satellites of Fe 2+ and Fe 3+ , which relates to the shakeup excitations in XPS, characterized by a satellite peak at higher BEs. 56,57 The peaks shown in Figure S9 59,60 The O II reveals the surface oxidation of the Se species, persistent with the Se 3d spectra. 59,60 The O III contribution is related to the physi-/chemisorbed water on the surfaces because of the exposure of air.…”