Maghemite
Encyclopedia
Maghemite is a member of the family of iron oxide
s. It has the same structure as magnetite
, that is, it is spinel
ferrite
and is also ferrimagnetic.
Maghemite can be considered as an Fe(II)-deficient magnetite with formula
where
represents a vacancy, 
indicates tetrahedral positioning and 
octahedral.
or low-temperature oxidation of spinel
s containing iron(II) such as magnetite or titanian magnetite. It occurs as widespread yellow pigment
in terrestrial sediment
s and soils. It is associated with magnetite, ilmenite
, anatase
, pyrite
, marcasite
, lepidocrocite
and goethite
.
Maghemite was named in 1927 for an occurrence at the Iron Mountain mine, northwest of Redding
, Shasta County, California
. The name alludes to somewhat intermediate character between MAGnetite and HEMatite. It is blue with a grey shade, white, or brown. It has isometric
crystals. Maghemite is formed by the topotactic
oxidation of magnetite
.
.
with a bandgap of around 2 eV, although the precise value of the gap depends on the electron spin
.
(~950 K), which together with its low cost and chemical stability led to its wide application as a magnetic pigment in electronic recording media since the 1940s.
Maghemite nanoparticles are also used in biomedicine
, because they are biocompatible and non-toxic to humans, while their magnetism allows remote manipulation with external fields.
Iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...
s. It has the same structure as magnetite
Magnetite
Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...
, that is, it is spinel
Spinel
Spinel is the magnesium aluminium member of the larger spinel group of minerals. It has the formula MgAl2O4. Balas ruby is an old name for a rose-tinted variety.-Spinel group:...
ferrite
Ferrite (magnet)
Ferrites are chemical compounds consisting of ceramic materials with iron oxide as their principal component. Many of them are magnetic materials and they are used to make permanent magnets, ferrite cores for transformers, and in various other applications.Many ferrites are spinels with the...
and is also ferrimagnetic.
Maghemite can be considered as an Fe(II)-deficient magnetite with formula
where represents a vacancy, indicates tetrahedral positioning and octahedral.Occurrence
Maghemite forms by weatheringWeathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
or low-temperature oxidation of spinel
Spinel
Spinel is the magnesium aluminium member of the larger spinel group of minerals. It has the formula MgAl2O4. Balas ruby is an old name for a rose-tinted variety.-Spinel group:...
s containing iron(II) such as magnetite or titanian magnetite. It occurs as widespread yellow pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
in terrestrial sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
s and soils. It is associated with magnetite, ilmenite
Ilmenite
Ilmenite is a weakly magnetic titanium-iron oxide mineral which is iron-black or steel-gray. It is a crystalline iron titanium oxide . It crystallizes in the trigonal system, and it has the same crystal structure as corundum and hematite....
, anatase
Anatase
Anatase is one of the three mineral forms of titanium dioxide, the other two being brookite and rutile. It is always found as small, isolated and sharply developed crystals, and like rutile, a more commonly occurring modification of titanium dioxide, it crystallizes in the tetragonal system; but,...
, pyrite
Pyrite
The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...
, marcasite
Marcasite
The mineral marcasite, sometimes called white iron pyrite, is iron sulfide with orthorhombic crystal structure. It is physically and crystallographically distinct from pyrite, which is iron sulfide with cubic crystal structure. Both structures do have in common that they contain the disulfide...
, lepidocrocite
Lepidocrocite
Lepidocrocite , also called esmeraldite or hydrohematite, is an iron oxide-hydroxide mineral. Lepidocrocite has an orthorhombic crystal structure, a hardness of 5, specific gravity of 4, a submetallic luster and a yellow-brown streak. It is red to reddish brown and forms when iron-containing...
and goethite
Goethite
Goethite , named after the German polymath Johann Wolfgang von Goethe, is an iron bearing oxide mineral found in soil and other low-temperature environments. Goethite has been well known since prehistoric times for its use as a pigment. Evidence has been found of its use in paint pigment samples...
.
Maghemite was named in 1927 for an occurrence at the Iron Mountain mine, northwest of Redding
Redding, California
Redding is a city in far-Northern California. It is the county seat of Shasta County, California, USA. With a population of 89,861, according to the 2010 Census...
, Shasta County, California
Shasta County, California
Shasta County is a county located in the northern portion of the U.S. state of California. The county occupies the northern reaches of the Sacramento Valley, with portions extending into the southern reaches of the Cascade Range. As of the 2010 census, the population was 177,223, up from 163,256...
. The name alludes to somewhat intermediate character between MAGnetite and HEMatite. It is blue with a grey shade, white, or brown. It has isometric
Cubic crystal system
In crystallography, the cubic crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals....
crystals. Maghemite is formed by the topotactic
Topotactic
In chemistry, a topotactic transition involves a structural change to a crystalline solid, which may include loss or gain of material, so that the final lattice is related to that of the original material by one or more crystallographically equivalent, orientational relationships.An example is a...
oxidation of magnetite
Magnetite
Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...
.
Cation distribution
There is experimental and theoretical evidence that Fe(III) cations and vacancies tend to be ordered in the octahedral sites, in a way that maximizes the homogeneity of the distribution and therefore minimizes the electrostatic energy of the crystalCrystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
.
Electronic structure
Maghemite is a semiconductorSemiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
with a bandgap of around 2 eV, although the precise value of the gap depends on the electron spin
Spin (physics)
In quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,...
.
Applications
Maghemite exhibits ferrimagnetic ordering with a high Néel temperatureNéel temperature
The Néel temperature or magnetic ordering temperature , TN, is the temperature above which an antiferromagnetic material becomes paramagnetic—that is, the thermal energy becomes large enough to destroy the macroscopic magnetic ordering within the material....
(~950 K), which together with its low cost and chemical stability led to its wide application as a magnetic pigment in electronic recording media since the 1940s.
Maghemite nanoparticles are also used in biomedicine
Biomedicine
Biomedicine is a branch of medical science that applies biological and other natural-science principles to clinical practice,. Biomedicine, i.e. medical research, involves the study of physiological processes with methods from biology, chemistry and physics. Approaches range from understanding...
, because they are biocompatible and non-toxic to humans, while their magnetism allows remote manipulation with external fields.