Magnetic analysis of commercial hematite, magnetite, and their mixtures

Abstract

Magnetic techniques are suitable to detect iron oxides even in trace concentrations. However, since several iron oxides may be simultaneously present in natural and synthetic samples, mixtures of magnetic particles and magnetic interactions between grains can complicate magnetic signatures. Among the iron oxide minerals, hematite (α-Fe2O3) and magnetite (Fe3O4) are the most common. In this work, different commercial hematite powders, normally used as Fe precursor in laboratory synthesis of Fe-containing oxides, were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). The effects of different concentrations of the hematite and magnetite on the magnetic properties of a set of mixtures (from 1 to 10 wt% magnetite) were then investigated by measuring the hysteresis loops, first order reversal curves (FORCs), thermal demagnetization, and isothermal remanent magnetization (IRM) curves. The three commercial hematite powders presented different magnetic behaviors mostly due to the effects of particle size. The magnetic results of mixtures reveal that it is very difficult to identify hematite magnetic signals by means of hysteresis loops, FORCs, or thermal demagnetization when even a small amount of magnetite (>5 wt%) is present due to magnetite’s high specific magnetization. However, IRM was found to be a sensitive method to determine the presence of hematite when magnetite is simultaneously present as high as 10 wt%.

Effect of Polymer Removal on the Morphology and Phase of the Nanoparticles in All-Inorganic Heterostructures Synthesized via Two-Step Polymer Infiltration

“…Magnetic property measurements ( Figure 4 ) indicate that all samples demonstrated significantly lower magnetization, M s , (less than ~20 emu/g calculated by dividing the magnetization by the mass of iron oxide NPs in the samples) at 5 K as compared to bulk ferromagnetic γ-Fe 2 O 3 (74 emu/g) and ferrimagnetic Fe 3 O 4 (84 emu/g) [ 42 ]; however, these were significantly higher than those of antiferromagnetic hematite α-Fe 2 O 3 (0.4 emu/g) [ 43 ] and goethite FeOOH (0.31 emu/g) [ 44 ] ( Figure 4 a). The low saturation magnetization can be a result of a surface spin disorder in ferro or ferrimagnetic NPs due to broken spins and canting of the surface spins; thus, the saturation requires a very high magnetic field.…”

“…However, at 300 K, the sample annealed at 450 °C has a higher magnetization over the whole applied magnetic field range ( Figure 4 b). Also, at 300 K, the sample with polymer and the sample that underwent UV ozone treatment show zero coercivities, while the sample after the thermal annealing shows coercivity of ~35 Oe, which could be due to structural defects [ 47 ] or indicative of some contribution of antiferromagnetic phase(s) that is (are) characterized by high coercivities [ 43 , 44 ]. The zero field cooling (ZFC) and field cooling (FC) data indicate the ferromagnetic response of all samples ( Figure 4 c).…”

Structure‐Dependent Electrical and Magnetic Properties of Iron Oxide Composites

“…At room temperature, i.e., above the Morin transition of Fe 2 O 3 , the moment in the (111) plane aligns at an angle giving weak ferromagnetism from the canting of spins, which shows up in the hysteresis plot . Fe 3 O 4 has inverse spinel structure with Fe 3+ ions aligned antiferromagnetically, and Fe 2+ ions aligned with the magnetic direction giving a net ferromagnetism much higher than that observed in Fe 2 O 3 . The in situ composite (Comp‐II) has a major contribution from Fe 2 O 3 hence exhibiting very similar saturation magnetism, while a decrease in the coercivity is observed in Figure (b).…”

Assessment of Magnetic Techniques for Understanding Complex Mixtures of Magnetite and Hematite: The Inuyama Red Chert

“…Ahmadzadeh et al. (2018) concluded that it is challenging to identify hematite using hysteresis loops, FORCs, or thermal demagnetization when magnetite contributes more than 5 wt‐% to the mixture. Ahmadzadeh et al.…”