Magnetite

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Magnetite
Magnetite-118736.jpg
Magnetite from Bolivia
General
Category
Formula
(repeating unit)		iron(II,III) oxide, Fe2+Fe3+2O4
IMA symbol Mag [1]
Strunz classification 4.BB.05
Crystal system Isometric
Crystal class Hexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space group Fd3m (no. 227)
Unit cell a = 8.397 Å; Z = 8
Identification
ColorBlack, gray with brownish tint in reflected sun
Crystal habit Octahedral, fine granular to massive
Twinning On {Ill} as both twin and composition plane, the spinel law, as contact twins
Cleavage Indistinct, parting on {Ill}, very good
Fracture Uneven
Tenacity Brittle
Mohs scale hardness5.5–6.5
Luster Metallic
Streak Black
Diaphaneity Opaque
Specific gravity 5.17–5.18
Solubility Dissolves slowly in hydrochloric acid
References [2] [3] [4] [5]
Major varieties
Lodestone Magnetic with definite north and south poles
Magnetite is one of the very few minerals that is ferrimagnetic; it is attracted by a magnet as shown here Magnetite sample with neodymium magnet.jpg
Magnetite is one of the very few minerals that is ferrimagnetic; it is attracted by a magnet as shown here
Unit cell of magnetite. The gray spheres are oxygen, green are divalent iron, blue are trivalent iron. Also shown are an iron atom in an octahedral space (light blue) and another in a tetrahedral space (gray). Kristallstruktur Magnetit.png
Unit cell of magnetite. The gray spheres are oxygen, green are divalent iron, blue are trivalent iron. Also shown are an iron atom in an octahedral space (light blue) and another in a tetrahedral space (gray).

Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; [6] it is attracted to a magnet and can be magnetized to become a permanent magnet itself. [7] [8] With the exception of extremely rare native iron deposits, it is the most magnetic of all the naturally occurring minerals on Earth. [7] [9] Naturally magnetized pieces of magnetite, called lodestone, will attract small pieces of iron, which is how ancient peoples first discovered the property of magnetism. [10]

Contents

Magnetite is black or brownish-black with a metallic luster, has a Mohs hardness of 5–6 and leaves a black streak. [7] Small grains of magnetite are very common in igneous and metamorphic rocks. [11]

The chemical IUPAC name is iron(II,III) oxide and the common chemical name is ferrous-ferric oxide. [12]

Properties

In addition to igneous rocks, magnetite also occurs in sedimentary rocks, including banded iron formations and in lake and marine sediments as both detrital grains and as magnetofossils. Magnetite nanoparticles are also thought to form in soils, where they probably oxidize rapidly to maghemite. [13]

Crystal structure

The chemical composition of magnetite is Fe2+(Fe3+)2(O2-)4. This indicates that magnetite contains both ferrous (divalent) and ferric (trivalent) iron, suggesting crystallization in an environment containing intermediate levels of oxygen. [14] [15] The main details of its structure were established in 1915. It was one of the first crystal structures to be obtained using X-ray diffraction. The structure is inverse spinel, with O2- ions forming a face-centered cubic lattice and iron cations occupying interstitial sites. Half of the Fe3+ cations occupy tetrahedral sites while the other half, along with Fe2+ cations, occupy octahedral sites. The unit cell consists of thirty-two O2- ions and unit cell length is a = 0.839 nm. [15] [16]

As a member of the inverse spinel group, magnetite can form solid solutions with similarly structured minerals, including ulvospinel (Fe2TiO4) and magnesioferrite (MgFe2O4). [17]

Titanomagnetite, also known as titaniferous magnetite, is a solid solution between magnetite and ulvospinel that crystallizes in many mafic igneous rocks. Titanomagnetite may undergo oxy-exsolution during cooling, resulting in ingrowths of magnetite and ilmenite. [17]

Crystal morphology and size

Natural and synthetic magnetite occurs most commonly as octahedral crystals bounded by {111} planes and as rhombic-dodecahedra. [15] Twinning occurs on the {111} plane. [3]

Hydrothermal synthesis usually produces single octahedral crystals which can be as large as 10 mm (0.39 in) across. [15] In the presence of mineralizers such as 0.1 M HI or 2 M NH4Cl and at 0.207  MPa at 416–800 °C, magnetite grew as crystals whose shapes were a combination of rhombic-dodechahedra forms. [15] The crystals were more rounded than usual. The appearance of higher forms was considered as a result from a decrease in the surface energies caused by the lower surface to volume ratio in the rounded crystals. [15]

Reactions

Magnetite has been important in understanding the conditions under which rocks form. Magnetite reacts with oxygen to produce hematite, and the mineral pair forms a buffer that can control how oxidizing its environment is (the oxygen fugacity). This buffer is known as the hematite-magnetite or HM buffer. At lower oxygen levels, magnetite can form a buffer with quartz and fayalite known as the QFM buffer. At still lower oxygen levels, magnetite forms a buffer with wüstite known as the MW buffer. The QFM and MW buffers have been used extensively in laboratory experiments on rock chemistry. The QFM buffer, in particular, produces an oxygen fugacity close to that of most igneous rocks. [18] [19]

Commonly, igneous rocks contain solid solutions of both titanomagnetite and hemoilmenite or titanohematite. Compositions of the mineral pairs are used to calculate oxygen fugacity: a range of oxidizing conditions are found in magmas and the oxidation state helps to determine how the magmas might evolve by fractional crystallization. [20] Magnetite also is produced from peridotites and dunites by serpentinization. [21]

Magnetic properties

Lodestones were used as an early form of magnetic compass. Magnetite has been a critical tool in paleomagnetism, a science important in understanding plate tectonics and as historic data for magnetohydrodynamics and other scientific fields. [22]

The relationships between magnetite and other iron oxide minerals such as ilmenite, hematite, and ulvospinel have been much studied; the reactions between these minerals and oxygen influence how and when magnetite preserves a record of the Earth's magnetic field. [23]

At low temperatures, magnetite undergoes a crystal structure phase transition from a monoclinic structure to a cubic structure known as the Verwey transition. Optical studies show that this metal to insulator transition is sharp and occurs around 120 K. [24] The Verwey transition is dependent on grain size, domain state, pressure, [25] and the iron-oxygen stoichiometry. [26] An isotropic point also occurs near the Verwey transition around 130 K, at which point the sign of the magnetocrystalline anisotropy constant changes from positive to negative. [27] The Curie temperature of magnetite is 580 °C (853 K; 1,076 °F). [28]

If magnetite is in a large enough quantity it can be found in aeromagnetic surveys using a magnetometer which measures magnetic intensities. [29]

Melting point

Solid magnetite particles melt at about 1,583–1,597 °C (2,881–2,907 °F). [30] [31] : 794 

Distribution of deposits

Magnetite and other heavy minerals (dark) in a quartz beach sand (Chennai, India). HeavyMineralsBeachSand.jpg
Magnetite and other heavy minerals (dark) in a quartz beach sand (Chennai, India).

Magnetite is sometimes found in large quantities in beach sand. Such black sands (mineral sands or iron sands) are found in various places, such as Lung Kwu Tan in Hong Kong; California, United States; and the west coast of the North Island of New Zealand. [32] The magnetite, eroded from rocks, is carried to the beach by rivers and concentrated by wave action and currents. Huge deposits have been found in banded iron formations. [33] [34] These sedimentary rocks have been used to infer changes in the oxygen content of the atmosphere of the Earth. [35]

Large deposits of magnetite are also found in the Atacama region of Chile (Chilean Iron Belt); [36] the Valentines region of Uruguay; [37] Kiruna, Sweden; [38] the Tallawang region of New South Wales; [39] and in the Adirondack Mountains of New York in the United States. [40] Kediet ej Jill, the highest mountain of Mauritania, is made entirely of the mineral. [41] In the municipalities of Molinaseca, Albares, and Rabanal del Camino, in the province of León (Spain), there is a magnetite deposit in Ordovician terrain, considered one of the largest in Europe. It was exploited between 1955 and 1982. [42] Deposits are also found in Norway, Romania, and Ukraine. [43] Magnetite-rich sand dunes are found in southern Peru. [44] In 2005, an exploration company, Cardero Resources, discovered a vast deposit of magnetite-bearing sand dunes in Peru. The dune field covers 250 square kilometers (100 sq mi), with the highest dune at over 2,000 meters (6,560 ft) above the desert floor. The sand contains 10% magnetite. [45]

In large enough quantities magnetite can affect compass navigation. In Tasmania there are many areas with highly magnetized rocks that can greatly influence compasses. Extra steps and repeated observations are required when using a compass in Tasmania to keep navigation problems to the minimum. [46]

Magnetite crystals with a cubic habit are rare but have been found at Balmat, St. Lawrence County, New York, [47] [48] and at Långban, Sweden. [49] This habit may be a result of crystallization in the presence of cations such as zinc. [50]

Magnetite can also be found in fossils due to biomineralization and are referred to as magnetofossils. [51] There are also instances of magnetite with origins in space coming from meteorites. [52]

Biological occurrences

Biomagnetism is usually related to the presence of biogenic crystals of magnetite, which occur widely in organisms. [53] These organisms range from magnetotactic bacteria (e.g., Magnetospirillum magnetotacticum ) to animals, including humans, where magnetite crystals (and other magnetically sensitive compounds) are found in different organs, depending on the species. [54] [55] Biomagnetites account for the effects of weak magnetic fields on biological systems. [56] There is also a chemical basis for cellular sensitivity to electric and magnetic fields (galvanotaxis). [57]

Magnetite magnetosomes in Gammaproteobacteria Magnetite magnetosomes in Gammaproteobacteria.png
Magnetite magnetosomes in Gammaproteobacteria

Pure magnetite particles are biomineralized in magnetosomes, which are produced by several species of magnetotactic bacteria. Magnetosomes consist of long chains of oriented magnetite particle that are used by bacteria for navigation. After the death of these bacteria, the magnetite particles in magnetosomes may be preserved in sediments as magnetofossils. Some types of anaerobic bacteria that are not magnetotactic can also create magnetite in oxygen free sediments by reducing amorphic ferric oxide to magnetite. [58]

Several species of birds are known to incorporate magnetite crystals in the upper beak for magnetoreception, [59] which (in conjunction with cryptochromes in the retina) gives them the ability to sense the direction, polarity, and magnitude of the ambient magnetic field. [54] [60]

Chitons, a type of mollusk, have a tongue-like structure known as a radula, covered with magnetite-coated teeth, or denticles. [61] The hardness of the magnetite helps in breaking down food.

Biological magnetite may store information about the magnetic fields the organism was exposed to, potentially allowing scientists to learn about the migration of the organism or about changes in the Earth's magnetic field over time. [62]

Human brain

Living organisms can produce magnetite. [55] In humans, magnetite can be found in various parts of the brain including the frontal, parietal, occipital, and temporal lobes, brainstem, cerebellum and basal ganglia. [55] [63] Iron can be found in three forms in the brain – magnetite, hemoglobin (blood) and ferritin (protein), and areas of the brain related to motor function generally contain more iron. [63] [64] Magnetite can be found in the hippocampus. The hippocampus is associated with information processing, specifically learning and memory. [63] However, magnetite can have toxic effects due to its charge or magnetic nature and its involvement in oxidative stress or the production of free radicals. [65] Research suggests that beta-amyloid plaques and tau proteins associated with neurodegenerative disease frequently occur after oxidative stress and the build-up of iron. [63]

Some researchers also suggest that humans possess a magnetic sense, [66] proposing that this could allow certain people to use magnetoreception for navigation. [67] The role of magnetite in the brain is still not well understood, and there has been a general lag in applying more modern, interdisciplinary techniques to the study of biomagnetism. [68]

Electron microscope scans of human brain-tissue samples are able to differentiate between magnetite produced by the body's own cells and magnetite absorbed from airborne pollution, the natural forms being jagged and crystalline, while magnetite pollution occurs as rounded nanoparticles. Potentially a human health hazard, airborne magnetite is a result of pollution (specifically combustion). These nanoparticles can travel to the brain via the olfactory nerve, increasing the concentration of magnetite in the brain. [63] [65] In some brain samples, the nanoparticle pollution outnumbers the natural particles by as much as 100:1, and such pollution-borne magnetite particles may be linked to abnormal neural deterioration. In one study, the characteristic nanoparticles were found in the brains of 37 people: 29 of these, aged 3 to 85, had lived and died in Mexico City, a significant air pollution hotspot. Some of the further eight, aged 62 to 92, from Manchester, England, had died with varying severities of neurodegenerative diseases. [69] Such particles could conceivably contribute to diseases like Alzheimer's disease. [70] Though a causal link has not yet been established, laboratory studies suggest that iron oxides such as magnetite are a component of protein plaques in the brain. Such plaques have been linked to Alzheimer's disease. [71]

Increased iron levels, specifically magnetic iron, have been found in portions of the brain in Alzheimer's patients. [72] Monitoring changes in iron concentrations may make it possible to detect the loss of neurons and the development of neurodegenerative diseases prior to the onset of symptoms [64] [72] due to the relationship between magnetite and ferritin. [63] In tissue, magnetite and ferritin can produce small magnetic fields which will interact with magnetic resonance imaging (MRI) creating contrast. [72] Huntington patients have not shown increased magnetite levels; however, high levels have been found in study mice. [63]

Applications

Due to its high iron content, magnetite has long been a major iron ore. [73] It is reduced in blast furnaces to pig iron or sponge iron for conversion to steel. [74]

Magnetic recording

Audio recording using magnetic acetate tape was developed in the 1930s. The German magnetophon first utilized magnetite powder that BASF coated onto cellulose acetate before soon switching to gamma ferric oxide for its superior morphology. [75] Following World War II, 3M Company continued work on the German design. In 1946, the 3M researchers found they could also improve their own magnetite-based paper tape, which utilized powders of cubic crystals, by replacing the magnetite with needle-shaped particles of gamma ferric oxide (γ-Fe2O3). [75]

Catalysis

Approximately 2–3% of the world's energy budget is allocated to the Haber Process for nitrogen fixation, which relies on magnetite-derived catalysts. The industrial catalyst is obtained from finely ground iron powder, which is usually obtained by reduction of high-purity magnetite. The pulverized iron metal is burnt (oxidized) to give magnetite or wüstite of a defined particle size. The magnetite (or wüstite) particles are then partially reduced, removing some of the oxygen in the process. The resulting catalyst particles consist of a core of magnetite, encased in a shell of wüstite, which in turn is surrounded by an outer shell of iron metal. The catalyst maintains most of its bulk volume during the reduction, resulting in a highly porous high-surface-area material, which enhances its effectiveness as a catalyst. [76] [77]

Magnetite nanoparticles

Magnetite micro- and nanoparticles are used in a variety of applications, from biomedical to environmental. One use is in water purification: in high gradient magnetic separation, magnetite nanoparticles introduced into contaminated water will bind to the suspended particles (solids, bacteria, or plankton, for example) and settle to the bottom of the fluid, allowing the contaminants to be removed and the magnetite particles to be recycled and reused. [78] This method works with radioactive and carcinogenic particles as well, making it an important cleanup tool in the case of heavy metals introduced into water systems. [79]

Another application of magnetic nanoparticles is in the creation of ferrofluids. These are used in several ways. Ferrofluids can be used for targeted drug delivery in the human body. [78] The magnetization of the particles bound with drug molecules allows "magnetic dragging" of the solution to the desired area of the body. This would allow the treatment of only a small area of the body, rather than the body as a whole, and could be highly useful in cancer treatment, among other things. Ferrofluids are also used in magnetic resonance imaging (MRI) technology. [80]

Coal mining industry

For the separation of coal from waste, dense medium baths were used. This technique employed the difference in densities between coal (1.3–1.4 tonnes per m3) and shales (2.2–2.4 tonnes per m3). In a medium with intermediate density (water with magnetite), stones sank and coal floated. [81]

Magnetene

Magnetene is a two-dimensional flat sheet of magnetite noted for its ultra-low-friction properties. [82]

See also

Related Research Articles

<span class="mw-page-title-main">Hematite</span> Common iron oxide mineral

Hematite, also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of Fe
2O
3. It has the same crystal structure as corundum (Al
2O
3) and ilmenite (FeTiO
3). With this it forms a complete solid solution at temperatures above 950 °C (1,740 °F).

<span class="mw-page-title-main">Limonite</span> Hydrated iron oxide mineral

Limonite is an iron ore consisting of a mixture of hydrated iron(III) oxide-hydroxides in varying composition. The generic formula is frequently written as FeO(OH)·nH2O, although this is not entirely accurate as the ratio of oxide to hydroxide can vary quite widely. Limonite is one of the three principal iron ores, the others being hematite and magnetite, and has been mined for the production of iron since at least 400 BC.

<span class="mw-page-title-main">Goethite</span> Iron(III) oxide-hydroxide named in honor to the poet Goethe

Goethite is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the α-polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient times for its use as a pigment. Evidence has been found of its use in paint pigment samples taken from the caves of Lascaux in France. It was first described in 1806 based on samples found in the Hollertszug Mine in Herdorf, Germany. The mineral was named after the German polymath and poet Johann Wolfgang von Goethe (1749–1832).

<span class="mw-page-title-main">Ilmenite</span> Titanium-iron oxide mineral

Ilmenite is a titanium-iron oxide mineral with the idealized formula FeTiO
3. It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printing inks, fabrics, plastics, paper, sunscreen, food and cosmetics.

<span class="mw-page-title-main">Wüstite</span> Iron(II) oxide (FeO) mineral formed under reducing conditions

Wüstite is a mineral form of mostly iron(II) oxide found with meteorites and native iron. It has a grey colour with a greenish tint in reflected light. Wüstite crystallizes in the isometric-hexoctahedral crystal system in opaque to translucent metallic grains. It has a Mohs hardness of 5 to 5.5 and a specific gravity of 5.88. Wüstite is a typical example of a non-stoichiometric compound.

<span class="mw-page-title-main">Chromite</span> Crystalline mineral

Chromite is a crystalline mineral composed primarily of iron(II) oxide and chromium(III) oxide compounds. It can be represented by the chemical formula of FeCr2O4. It is an oxide mineral belonging to the spinel group. The element magnesium can substitute for iron in variable amounts as it forms a solid solution with magnesiochromite (MgCr2O4). A substitution of the element aluminium can also occur, leading to hercynite (FeAl2O4). Chromite today is mined particularly to make stainless steel through the production of ferrochrome (FeCr), which is an iron-chromium alloy.

<span class="mw-page-title-main">Maghemite</span> Iron oxide with a spinel ferrite structure

Maghemite (Fe2O3, γ-Fe2O3) is a member of the family of iron oxides. It has the same formula as hematite, but the same spinel ferrite structure as magnetite (Fe3O4) and is also ferrimagnetic. It is sometimes spelled as "maghaemite".

<span class="mw-page-title-main">Iron(II,III) oxide</span> Chemical compound

Iron(II,III) oxide, or black iron oxide, is the chemical compound with formula Fe3O4. It occurs in nature as the mineral magnetite. It is one of a number of iron oxides, the others being iron(II) oxide (FeO), which is rare, and iron(III) oxide (Fe2O3) which also occurs naturally as the mineral hematite. It contains both Fe2+ and Fe3+ ions and is sometimes formulated as FeO ∙ Fe2O3. This iron oxide is encountered in the laboratory as a black powder. It exhibits permanent magnetism and is ferrimagnetic, but is sometimes incorrectly described as ferromagnetic. Its most extensive use is as a black pigment (see: Mars Black). For this purpose, it is synthesized rather than being extracted from the naturally occurring mineral as the particle size and shape can be varied by the method of production.

<span class="mw-page-title-main">Magnetosome</span> Organelle in magnetotactic bacteria

Magnetosomes are membranous structures present in magnetotactic bacteria (MTB). They contain iron-rich magnetic particles that are enclosed within a lipid bilayer membrane. Each magnetosome can often contain 15 to 20 magnetite crystals that form a chain which acts like a compass needle to orient magnetotactic bacteria in geomagnetic fields, thereby simplifying their search for their preferred microaerophilic environments. Recent research has shown that magnetosomes are invaginations of the inner membrane and not freestanding vesicles. Magnetite-bearing magnetosomes have also been found in eukaryotic magnetotactic algae, with each cell containing several thousand crystals.

<span class="mw-page-title-main">Biomineralization</span> Process by which living organisms produce minerals

Biomineralization, also written biomineralisation, is the process by which living organisms produce minerals, often resulting in hardened or stiffened mineralized tissues. It is an extremely widespread phenomenon: all six taxonomic kingdoms contain members that are able to form minerals, and over 60 different minerals have been identified in organisms. Examples include silicates in algae and diatoms, carbonates in invertebrates, and calcium phosphates and carbonates in vertebrates. These minerals often form structural features such as sea shells and the bone in mammals and birds.

Magnetotaxis is a process implemented by a diverse group of Gram-negative bacteria that involves orienting and coordinating movement in response to Earth's magnetic field. This process is mainly carried out by microaerophilic and anaerobic bacteria found in aquatic environments such as salt marshes, seawater, and freshwater lakes. By sensing the magnetic field, the bacteria are able to orient themselves towards environments with more favorable oxygen concentrations. This orientation towards more favorable oxygen concentrations allows the bacteria to reach these environments faster as opposed to random movement through Brownian motion.

<span class="mw-page-title-main">Magnetotactic bacteria</span> Polyphyletic group of bacteria

Magnetotactic bacteria are a polyphyletic group of bacteria that orient themselves along the magnetic field lines of Earth's magnetic field. Discovered in 1963 by Salvatore Bellini and rediscovered in 1975 by Richard Blakemore, this alignment is believed to aid these organisms in reaching regions of optimal oxygen concentration. To perform this task, these bacteria have organelles called magnetosomes that contain magnetic crystals. The biological phenomenon of microorganisms tending to move in response to the environment's magnetic characteristics is known as magnetotaxis. However, this term is misleading in that every other application of the term taxis involves a stimulus-response mechanism. In contrast to the magnetoreception of animals, the bacteria contain fixed magnets that force the bacteria into alignment—even dead cells are dragged into alignment, just like a compass needle.

<span class="mw-page-title-main">Mineral redox buffer</span> Geochemical assemblage

In geology, a redox buffer is an assemblage of minerals or compounds that constrains oxygen fugacity as a function of temperature. Knowledge of the redox conditions (or equivalently, oxygen fugacities) at which a rock forms and evolves can be important for interpreting the rock history. Iron, sulfur, and manganese are three of the relatively abundant elements in the Earth's crust that occur in more than one oxidation state. For instance, iron, the fourth most abundant element in the crust, exists as native iron, ferrous iron (Fe2+), and ferric iron (Fe3+). The redox state of a rock affects the relative proportions of the oxidation states of these elements and hence may determine both the minerals present and their compositions. If a rock contains pure minerals that constitute a redox buffer, then the oxygen fugacity of equilibration is defined by one of the curves in the accompanying fugacity-temperature diagram.

Magnetobiology is the study of biological effects of mainly weak static and low-frequency magnetic fields, which do not cause heating of tissues. Magnetobiological effects have unique features that obviously distinguish them from thermal effects; often they are observed for alternating magnetic fields just in separate frequency and amplitude intervals. Also, they are dependent of simultaneously present static magnetic or electric fields and their polarization.

<span class="mw-page-title-main">Magnetofossil</span> Fossils produced by magnetotactic bacteria

Magnetofossils are the fossil remains of magnetic particles produced by magnetotactic bacteria (magnetobacteria) and preserved in the geologic record. The oldest definitive magnetofossils formed of the mineral magnetite come from the Cretaceous chalk beds of southern England, while magnetofossil reports, not considered to be robust, extend on Earth to the 1.9-billion-year-old Gunflint Chert; they may include the four-billion-year-old Martian meteorite ALH84001.

<span class="mw-page-title-main">Mars surface color</span> Extraterrestrial geography

The surface color of the planet Mars appears reddish from a distance because of rusty atmospheric dust. From close up, it looks more of a butterscotch, and other common surface colors include golden, brown, tan, and greenish, depending on minerals.

Magnetic nanoparticles (MNPs) are a class of nanoparticle that can be manipulated using magnetic fields. Such particles commonly consist of two components, a magnetic material, often iron, nickel and cobalt, and a chemical component that has functionality. While nanoparticles are smaller than 1 micrometer in diameter, the larger microbeads are 0.5–500 micrometer in diameter. Magnetic nanoparticle clusters that are composed of a number of individual magnetic nanoparticles are known as magnetic nanobeads with a diameter of 50–200 nanometers. Magnetic nanoparticle clusters are a basis for their further magnetic assembly into magnetic nanochains. The magnetic nanoparticles have been the focus of much research recently because they possess attractive properties which could see potential use in catalysis including nanomaterial-based catalysts, biomedicine and tissue specific targeting, magnetically tunable colloidal photonic crystals, microfluidics, magnetic resonance imaging, magnetic particle imaging, data storage, environmental remediation, nanofluids, optical filters, defect sensor, magnetic cooling and cation sensors.

<span class="mw-page-title-main">Iron oxide nanoparticle</span>

Iron oxide nanoparticles are iron oxide particles with diameters between about 1 and 100 nanometers. The two main forms are composed of magnetite and its oxidized form maghemite. They have attracted extensive interest due to their superparamagnetic properties and their potential applications in many fields including molecular imaging.

Environmental magnetism is the study of magnetism as it relates to the effects of climate, sediment transport, pollution and other environmental influences on magnetic minerals. It makes use of techniques from rock magnetism and magnetic mineralogy. The magnetic properties of minerals are used as proxies for environmental change in applications such as paleoclimate, paleoceanography, studies of the provenance of sediments, pollution and archeology. The main advantages of using magnetic measurements are that magnetic minerals are almost ubiquitous and magnetic measurements are quick and non-invasive.

Barbara Ann Maher is a Professor Emerita of Environmental Science at Lancaster University. She served as director of the Centre for Environmental magnetism & Palaeomagnetism until 2021 and works on magnetic nanoparticles and pollution.

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