Hexagonal Magnetite Research Articles

Multi-Level Switching of Spin-Torque Ferromagnetic Resonance in 2D Magnetite.

2D magnetic materials hold substantial promise in information storage and neuromorphic device applications. However, achieving a 2D material with high Curie temperature (TC), environmental stability, and multi-level magnetic states remains a challenge. This is particularly relevant for spintronic devices, which require multi-level resistance states to enhance memory density and fulfil low power consumption and multi-functionality. Here, the synthesis of 2D non-layered triangular and hexagonal magnetite (Fe3O4) nanosheets are proposed with high TC and environmental stability, and demonstrate that the ultrathin triangular nanosheets show broad antiphase boundaries (bAPBs) and sharp antiphase boundaries (sAPBs), which induce multiple spin precession modes and multi-level resistance. Conversely, the hexagonal nanosheets display slip bands with sAPBs associated with pinning effects, resulting in magnetic-field-driven spin texture reversal reminiscent of "0" and "1" switching signals. In support of the micromagnetic simulation, direct explanation is offer to the variation in multi-level resistance under a microwave field, which is ascribed to the multi-spin texture magnetization structure and the randomly distributed APBs within the material. These novel 2D magnetite nanosheets with unique spin textures and spin dynamics provide an exciting platform for constructing real multi-level storage devices catering to emerging information storage and neuromorphic computing requirements.

Hexagonal magnetite in Algoma-type banded iron formations of the ca. 2.52 Ga Baizhiyan Formation, North China: Evidence for a green rust precursor?

Abstract Banded iron formations (BIFs) are iron-rich marine chemical sedimentary rocks, and their mineralogy and geochemistry can be used to gain insights into ancient ocean chemistry and biospheric evolution. Magnetite is the major iron-bearing mineral in many BIFs (particularly in the Archean) and is variably interpreted to be of primary, early diagenetic, or metamorphic origin. Different genetic interpretations for magnetite lead to divergent pictures of the Precambrian Earth system and its evolutionary models through time. The Baizhiyan Formation of the Neoarchean Wutai Group (Shanxi, North China) features magnetite-bearing, Algoma-type BIFs deposited ca. 2.52 Ga, in the lead-up to a major period of global iron formation deposition in the Paleoproterozoic. Abundant magnetite crystals found in the silica-rich bands of these BIFs show euhedral, hexagonal morphology. We suggest that this hexagonal magnetite likely represents pseudomorphs after green rust, a mixed-valence iron hydroxy-salt formed in the water column. The rare earth element composition of the BIFs shows negligible to slightly positive Ce anomalies (CeSN/CeSN* = 1.03 ± 0.07), which is characteristic of a dominantly anoxic water column. The presence of positive Eu anomalies (EuSN/EuSN* <3.9) suggests a substantial influence from proximal hydrothermal fluids. The co-occurrence of siderite layers associated with the magnetite-bearing strata may indicate iron cycling associated with ferruginous bottom seawater conditions. Geochemical signatures of the Baizhiyan BIFs are consistent with the interpretation that the magnetite was transformed from metastable green rust. This green rust could have formed via several processes, including the partial oxidation of Fe(II) by molecular oxygen/photoferrotrophs, the reaction of settling ferrihydrite with Fe(II)-rich hydrothermal fluids under anoxic conditions, or local dissimilatory iron reduction. In all cases, the contribution of primary green rust to BIF formation requires iron redox cycling, and similar pseudomorphs in the form of hexagonal magnetite may be more common in the geological record. Our findings support the models in which green rust was an important primary constituent of the Precambrian iron cycle, and the potential interactions of green rust with other elements (e.g., phosphorus) should be taken into consideration when reconstructing Precambrian biogeochemical cycles.

Microwave-Assisted Synthesis of Graphene Supported Hexagonal Magnetite for Applications in Catalysis

Herein, we report a rapid one-step synthetic method using microwave irradiation for growing magnetite nanocrystals on reduced graphene oxide sheets. This developed strategy allows decorating graphene sheets with magnetite nanocrystals of well-defined morphology as cubes using microwave-driven reduction of iron chloride using hydrazine hydrate as a reducing agent. The size and shape control was achieved via fine-tuning of the reaction conditions. The obtained results demonstrate the applicability of this microwave synthetic approach to control the morphology of the magnetite nanocrystals anchored on graphene sheets. Moreover, graphene sheets will enhance the nucleation and growth of magnetite nanoplates anchored on graphene. This approach can be used as a synthetic tool to synthesize a wide variety of metal and metal oxide architectures on graphene. This approach also provides plenty of advantages like catalyst recyclability, mild reaction conditions, easy separation, reproducibility, and minimization of agglomeration effect that cause the decrease in the catalyst catalytic activity.

Microwave-Assisted Synthesis of Graphene Supported Hexagonal Magnetite for Applications in Catalysis

Herein, we report a rapid one-step synthetic method using microwave irradiation for growing magnetite nanocrystals on reduced graphene oxide sheets. This developed strategy allows decorating graphene sheets with magnetite nanocrystals of welldefined morphology as cubes using microwave-driven reduction of iron chloride using hydrazine hydrate as a reducing agent. The size and shape control was achieved via fine-tuning of the reaction conditions. The obtained results demonstrate the applicability of this microwave synthetic approach to control the morphology of the magnetite nanocrystals anchored on graphene sheets. Moreover, graphene sheets will enhance the nucleation and growth of magnetite nanoplates anchored on graphene. This approach can be used as a synthetic tool to synthesize a wide variety of metal and metal oxide architectures on graphene. This approach also provides plenty of advantages like catalyst recyclability, mild reaction conditions, easy separation, reproducibility, and minimization of agglomeration effect that cause the decrease in the catalyst catalytic activity

Shape-control by microwave-assisted hydrothermal method for the synthesis of magnetite nanoparticles using organic additives

A simple and fast microwave-assisted hydrothermal method is proposed for the synthesis of magnetite nanoparticles. The addition of different surfactants (polyvinylpyrrolidone, oleic acid, or trisodium citrate) was studied to investigate the effect on size distribution, morphology, and functionalization of the magnetite nanoparticles. Microwave irradiation at 150 °C for 2 h of aqueous ferrous chloride and hydrazine without additives resulted in hexagonal magnetite nanoplatelets with a facet-to-facet distance of 116 nm and a thickness of 40 nm having a saturation magnetization of ~65 Am2 kg−1. The use of polyvinylpyrrolidone led to hexagonal nanoparticles with a facet-to-facet distance of 120 nm and a thickness of 53 nm with a saturation magnetization of ~54 Am2 kg−1. Additives such as oleic acid and trisodium citrate yielded quasi-spherical nanoparticles of 25 nm in size with a saturation magnetization of ~70 Am2 kg−1 and spheroidal nanoparticles of 60 nm in size with a saturation magnetization up to ~82 Am2 kg−1, respectively. A kinetic control of the crystal growth is believed to be responsible for the hexagonal habit of the nanoparticles obtained without additive. Conversely, a thermodynamic control of the crystal growth, leading to spheroidal nanoparticles, seems to occur when additives which strongly interact with the nanoparticle surface are used. A thorough characterization of the materials was performed. Magnetic properties were investigated by Superconducting Quantum Interference Device and Vibrating Sample magnetometers. Based on the observed magnetic properties, the magnetite obtained using citrate appears to be a promising support for magnetically transportable catalysts.

Hexagonal magnetite nanoprisms: preparation, characterization and cellular uptake.

The capacity of iron oxide nanocrystals to heat tissue when subjected to an alternating magnetic field (AMF hyperthermia) is shape-selective. Although iron oxide nanostructures with numerous shapes have been synthesized to date, hexagonal Fe3O4 prisms of low toxicity remained elusive. Here, we report the use of a dual ligand system permitting feasible reaction conditions to synthesize nearly perfect hexagonal Fe3O4 nanoplatelet structures, with edge length of 45 ± 5 nm and thickness of 5 to 6 nm. Their Specific Absorption Rate (SAR) is >750 W g(Fe)-1. The Fe3O4 hexagons were coated with a dopamine-based ligand to increase dispersibility in aqueous buffers. The Fe3O4 hexagons were only minimally toxic to RAW264.7 cells, which can be utilized in cell-based cancer targeting approaches.

Carbon-coated hexagonal magnetite nanoflakes production by spray CVD of alcohols in mixture with water

In this study, we report a successful technique for synthesizing magnetite hexagonal nanoflakes coated with carbon layers using spray thermal decomposition, which is a reproducible method that is easy to scale up. We investigated the effects of mixing different volumes of deionized (DI) water with alcohol on the population and quality of single-crystalline Fe3O4 hexagonal nanoflakes. Methanol and ethanol were used as the carbon and oxygen source, while ferrocene was mainly used as the Fe source. To obtain a large quantity of hexagonal structures, a strongly oxidative atmosphere was required. The DI water was used to enhance the oxidative environment during the reaction and was an important component for obtaining well-shaped hexagonal magnetite crystalline nanoflakes. The use of alcohols, water and the spray chemical vapor deposition (CVD) method make this procedure easy to use. In addition, this method provides a one-step process for synthesizing carbon-coated hexagonal Fe3O4 nanocrystals.

Facile synthesis and characterisation of hexagonal magnetite nanoplates

Hexagonal magnetite (Fe3O4) nanoplates were synthesised using a facile hydrothermal route, where ß-cyclodextrin and urea were used as a reducing agent and a modifier, respectively. It was found that the obtained hexagonal Fe3O4 nanoplates had an average diameter of about 400 nm and thickness in the range of 40–80 nm. The effects of the concentration of urea and pH value on the formation of Fe3O4 nanoplates are discussed. A possible formation mechanism for the hexagonal Fe3O4 nanoplates is proposed. Magnetic studies revealed that the hexagonal Fe3O4 nanoplates exhibited a relatively high saturation magnetisation of 78.93 emu/g and a coercivity of less than 200 Oe at room temperature, which indicates that the as-prepared Fe3O4 nanoplates are ferromagnetic.

Microwave-assisted synthesis and characterization of hexagonal Fe 3O 4 nanoplates

Hexagonal magnetite (Fe 3O 4) nanoplates with an average edge length of 80 nm were successfully prepared in large quantities by a facile microwave-assisted route. The influences of experiment parameters such as reaction time, microwave power, and concentration of NaOH and other additive agents on the morphology and size of final products were investigated in detail. Phase structure, morphology and magnetic properties of products were carefully studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), high-resolution transmission electron microscope (HRTEM), and vibrating sample magnetometer (VSM). Magnetic studies revealed that hexagonal Fe 3O 4 nanoplates have low saturation magnetization of 36.4 emu/g and the possible reason has been proposed.