Abstract
Greigite (Fe3S4) is a ferrimagnetic mineral with an inverse spinel structure. Besides its importance in the bio-geochemical cycle, it also has great potential applications for its unique properties such as its half metallic electronic structure at ambient condition. However, it has been challenging to get high purity and crystallinity samples of greigite in experiment, and the defect effect on the electronic structure of greigite was not clear. In the present study, first-principles calculations have been performed to investigate the ground state electronic structure of greigite with monovacancy. It is found that, with an vacancy concentration lower than 3.6%, the greigite with an Fe vacancy is an insulator with charge orderings, while the greigite with a S vacancy becomes a half-metal and has a magnetic moment of <4.0 μB per formula unit. The present result helps to understand the absence of the Verwey transition and the magnetic property of greigite measured in experiment. The understanding of the electronic structure of defective greigite could also be utilized to manipulate the properties of greigite for spintronic applications.
Highlights
Greigite (Fe3S4) was first discovered as a mineral by Skinner et al from Californian lake sediments[1], and its natural form was probably from the bacteriological reduction of iron[2]
First-principles calculations with hybrid functional method showed that the insulative monoclinic structure of greigite induced by charge ordering is energetically more stable than the half-metallic cubic phase, indicating the Verwey transition may exist in greigite[12]
It indicates the S vacancy should be the common vacancy if there is any existing in the defective greigite sample in experiment
Summary
Greigite (Fe3S4) was first discovered as a mineral by Skinner et al from Californian lake sediments[1], and its natural form was probably from the bacteriological reduction of iron[2]. Greigite is a sulfide counterpart of the well-known magnetite (Fe3O4)[11] It has an inverse spinel structure with one tetrahedral iron site and two octahedral iron sites per formula unit (Fe3+A(Fe2+BFe3+B)S2−4). It should be noticed that the metastable nature and the challenges in obtaining high-quality samples of greigite could be one of the reasons for the absence of the Verwey transition and its relatively low measured magnetic moment. The previous calculations using the Hubbard U method showed the electronic structure of greigite is highly sensitive to the effective U value[18]. First-principles calculations using the Heyd-Scuseria-Ernzerhof screened hybrid functional (HSE)[19] and Hubbard U methods were performed to investigate the ground state electronic structure and magnetic properties of greigite with monovacancy. The presented results show the defects have strong effects on the electronic structure of greigite and help to understand the properties of greigite measured in experiment
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