Ferromagnetism in 2D α-Fe2O3 nanosheets

Abstract

In this report, hematene (2D α-Fe2O3 nanosheets) with an exceptionally high coercivity of up to 7.5 kOe has been synthesized via a soft-chemical exfoliation process. The high coercivity correlates with the surface magnetic anisotropy that originates from enhanced uncompensated spin canting as a result of the 2D morphology. This observation is different from the behavior of the bulk counterpart that exhibits collinear antiferromagnetic ordering with no net magnetization at low temperatures. In addition, our study shows a suppression of the Morin transition in 2D nanosheets, which further confirms that the surface spins deviate strongly from the collinear antiferromagnetic ordering. We also observed a spin-glass-like transition with a rapid increase in saturation magnetization and a decrease in anisotropy in the ultra-thin α-Fe2O3 nanosheets at temperatures below 48 K. The spin-glass behavior is correlated with the observed exchange bias and the magnetic field dependence of spin-glass freezing temperature.

Data-Driven Quest for Two-Dimensional Non-van der Waals Materials

“…43 The first studies mostly focusing on hematene indicate, for instance, tunable magnetic ordering, 29,30,40,44−47 as well as spin canting. 48 Although there have been significant experimental efforts to generalize recipes for their synthesis, 37,38,41,47,50 computational design principles based on data-driven concepts for outlining non-vdW 2D materials are still missing. It is obvious that the descriptors developed for vdW-bonded systems are not applicable, since they rely on identifying layered subunits in the structure.…”

“…Moreover, they may also offer a versatile playground for magnetism and spintronics in reduced dimensions . The first studies mostly focusing on hematene indicate, for instance, tunable magnetic ordering, ,,,− as well as spin canting …”

Creation and modulation of ferromagnetism in antiferromagnetic hematite nanoplates

“…4b summarizes the reported magnetization values of the α-Fe 2 O 3 with different facets and various morphologies in the literature (detailed references are listed in ESI,† Table S3), and those found in this work. Compared with the {012}, 27 {104}, 28 {101}, {101}/{111}, 29 nanodisc, 30 nanoparticle, 31 3D nanoparticle, 17 2D nanosheet, 32 and nanorod 33 samples and other reported α-Fe 2 O 3 nanoparticles, 34 the as-prepared {001} samples, especially {001}-V, exhibit excellent ferromagnetism with a magnetization that is much higher than the average value of all the other samples so far reported. This strong magnetization makes α-Fe 2 O 3 an extraordinary candidate for catalysis, drug delivery, water splitting, and most importantly, spintronics.…”

Regulating Magnetic Behavior of Fe in Hematene by Defects to Improve Oxygen Evolution Reaction

“…18 The 2D hematene was first obtained from iron ore via a liquid exfoliation process, 19 which exhibits enhanced visible-light photocatalytic activity when it is loaded on TiO 2 nanotube arrays. Subsequently, the hematene was successfully synthesized by different experimental methods, i.e., sonication, 20 soft-chemical exfoliation, 21 and microwave liquid-phase synthesis. 22 The 2D hematene can be easily modulated and exhibits unique properties in comparison to its bulk counterpart.…”

“…The 2D hematene was first obtained from iron ore via a liquid exfoliation process, which exhibits enhanced visible-light photocatalytic activity when it is loaded on TiO 2 nanotube arrays. Subsequently, the hematene was successfully synthesized by different experimental methods, i.e., sonication, soft-chemical exfoliation, and microwave liquid-phase synthesis . The 2D hematene can be easily modulated and exhibits unique properties in comparison to its bulk counterpart. , Hematene has a narrower band gap compared to hematite, and it is an antiferromagnetic ground-state semiconductor. − Previous study revealed that the curie temperature increases monotonically with the compressive strains in hematene, which broadens its applications for spintronic, memory-based devices and valleytronics .…”